Special Science Teleclass: Thermodynamics

Monday December 1, 2014

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!


You’ll discover how to boil water at room temperature, heat up ice to freeze it, make a fire water balloon, and build a real working steam boat as you learn about heat energy. You’ll also learn about thermal energy, heat capacity, and the laws of thermodynamics.


Materials:


  • cup of ice water
  • cup of room temperature water
  • cup of hot water (not scalding or boiling!)
  • tea light candle and lighter (with adult help)
  • balloon (not inflated)
  • syringe (without the needle)
  • block of foam
  • copper tubing (¼” diameter and 12” long)
  • bathtub or sink
  • scissors or razor
  • fat marker (to be used to wrap things around, not for writing)

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Key Concepts

The terms hot, cold, warm etc. describe what physicists call thermal energy. Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy that object has.


There are three different scales for measuring temperature. Fahrenheit, Celsius and Kelvin. (There’s also a fourth temperature scale for absolute Fahrenheit called Rankine.) Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Your skin, mouth and tongue are antennas which can sense thermal energy.


There are four states of matter: Solid, liquid, gas and plasma. Solids have strong, stiff bonds between molecules that hold the molecules in place. Liquids have loose, stringy bonds between molecules that hold molecules together but allow them some flexibility. Gasses have no bonds between the molecules. Plasma is similar to gas but the molecules are very highly energized. Materials can change from one state to another depending on the temperature and the bonds. Changing from a solid to a liquid is called melting. Changing from a liquid to a gas is called boiling, evaporating, or vaporizing. Changing from a gas to a liquid is called condensation. Changing from a liquid to a solid is called freezing. All materials have given points at which they change from state to state. Melting point is the temperature at which a material changes from solid to liquid.  Boiling point is the temperature at which a material changes from liquid to gas. Condensation point is the temperature at which a material changes from gas to liquid. Freezing point is the temperature at which a material changes from liquid to gas.


What’s Going On?

Heat is the movement of thermal energy from one object to another. Heat can only flow from an object of a higher temperature to an object of a lower temperature (this is the First Law of Thermodynamics). Heat is movement of thermal energy from one object to another. When an object absorbs heat it does not necessarily change temperature.  Objects release heat as they freeze and condense. Objects absorb heat as they evaporate and melt. Freezing points, melting points, boiling points and condensation points are the “speed limits” of the phases. Once the molecules reach that speed they must change state.


Heat capacity is how much heat an object can absorb before its temperature increases. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C. Heat capacity is influenced by the specific heat of the material and/or the amount of the material. Each material has its own specific heat. The higher a material’s specific heat is, the more heat it must absorb before its temperature increases. A larger amount of something will have a higher heat capacity then a smaller amount of something. Water has a very high heat capacity.


Questions:

  1. True or False: Water is poor at absorbing heat energy.
  2. True or False: A molecule that heats up will move faster.
  3. True or False: A material will be less dense at lower temperatures.
  4. For gases, if we increase the temperature, what happens to the pressure and the volume?
  5. What is specific heat?
  6. What is heat?
  7. Does heat flow from cold to hot? Give an example.
  8. What do the our body sense, heat flow or temperature? Are they the same thing?
  9. How can we boil room temperature water without heating up the water?

Answers:


  1. False.
  2. True.
  3. False. (Usually.)
  4. If we increase the temperature, the pressure increases and the volume decreases. This is called the Ideal Gas Law (remember the ping pong balls from the teleclass?)
  5. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.
  6. Heat is the movement of thermal energy from one object to another.
  7. No. Heat flows from hot to cold. (This is the First Law of Thermodynamics.) A hot cup of coffee left out on a cold morning will eventually cool to the surrounding air temperature.
  8. Heat flow. No they are not the same thing. Temperature is a measure of how much energy the molecules have.
  9. By increasing the pressure by decreasing the volume, we can force the bubbles out of the water and it will boil. Boiling is when the liquid water turns into a gas, NOT when the liquid water heats up. Boiling can happen at many different temperatures when you change the pressure.

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Electric Current

Monday November 24, 2014

Imagine you have two metal plates that are parallel to each other, and one is positively charged ad the other is negatively charged. The direction of the electric field created by these two charged places is from the positive toward the negative plate. (Imagine placing a positive test charge int he field… which way would it go? Away from the positive plate and toward the negative plate… so that’s the direction of the electric field.) Now imagine connecting the two plates with a metal wire. What do you think would happen?


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The positive charges on the positive plate would flow toward the negative plate, evening out the charge until they were both at the same charge, and then there is no electric potential difference between the two. It’s like connecting a hose between two cups filled with different levels of water. The water flows out of the cup with more water into the one with less until they both even out. When the charges even out, there not charge flow because there’s no electrical potential difference.


Click here to go to your next lesson on Electric Circuits!

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Electric Circuits

Monday November 24, 2014

An electrical circuit is like a NASCAR raceway.  The electrons (racecars) zip around the race loop (wire circuit) superfast to make stuff happen. Although you can’t see the electrons zipping around the circuit, you can see the effects: lighting up LEDs, sounding buzzers, clicking relays, etc.


There are many different electrical components that make the electrons react in different ways, such as resistors (limit current), capacitors (collect a charge), transistors (gate for electrons), relays (electricity itself activates a switch), diodes (one-way street for electrons), solenoids (electrical magnet), switches (stoplight for electrons), and more.  We’re going to use a combination diode-light-bulb (LED), buzzers, and motors in our circuits right now.


A CIRCUIT looks like a CIRCLE.  When you connect the batteries to the LED with wire and make a circle, the LED lights up.  If you break open the circle, electricity (current) doesn’t flow and the LED turns dark.


LED stands for “Light Emitting Diode”.  Diodes are one-way streets for electricity – they allow electrons to flow one way but not the other.


Remember when you scuffed along the carpet?  You gathered up an electric charge in your body.  That charge was static until you zapped someone else.  The movement of electric charge is called electric current, and is measured in amperes (A). When electric current passes through a material, it does it by electrical conduction. There are different kinds of conduction, such as metallic conduction, where electrons flow through a conductor (like metal) and electrolysis, where charged atoms (called ions) flow through liquids.


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Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 2 alligator wires
  • LEDs (any you choose is fine)


Download Student Worksheet & Exercises


Be alert for:


1. Batteries inserted into the case the wrong way!


2. LED in the wrong way (LEDs are picky about plus and minus – they are POLARIZED)


3. Is there a metal-to-metal connection?  (You’re not grabbing ahold of the plastic insulation, are you?)


4. Bad wires can cause headaches – if all else fails, then swap out your alligator clip lead wires for new ones.


Exercises


  1. What does LED stand for?
  2. Does it matter which way you wire an LED in a circuit?
  3. Does the longer wire on the LED connect to plus (red) or minus (black)?
  4. Do you need to hook up batteries to make a neon bulb light up?  Why or why not?
  5. What’s the difference between a light bulb and your LED?
  6. What is the difference between a bolt of lightning and the electricity in your circuit?
  7. What is the charge of an electron?

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Click here to go to your next lesson on Detecting Current!

Detecting Current

Monday November 24, 2014

Galvanometers are coils of wire connected to a battery. When current flows through the wire, it creates a magnetic field. Since the wire is bundled up, it multiplies this electromagnetic effect to create a simple electromagnet that you can detect with your compass.
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Here’s what you need to do:


Materials:


  • magnet wire
  • sand paper
  • scissors
  • compass
  • AA battery case
  • 2 AA batteries
  • 2 alligator clip wires


Download Student Worksheet & Exercises


1. Remove the insulation from about an inch of each end of the wire. (Use sandpaper if you’re using magnet wire.)


2. Wrap the wire at least 30-50 times around your fingers, making sure your coil is large enough to slide the compass through.


3. Connect one end of the wire to the battery case wire.


4. While looking at the compass, repeatedly tap the other end of the wire to the battery. You should see the compass react to the tapping.


5. Switch the wires from one terminal of the battery to the other. Now tap again. Do you see a difference in the way the compass moves?


You just made a simple galvanometer. “Oh boy, that’s great! Hey Bob, take a look! I just made a….a what?!?” I thought you might ask that question. A galvanometer is a device that is used to find and measure electric current. “But, it made a compass needle move…isn’t that a magnetic field, not electricity?” Ah, yes, but hold on a minute. What is electric current…moving electrons. What do moving electrons create…a magnetic field! By the galvanometer detecting a change in the magnetic field, it is actually measuring electrical current! So, now that you’ve made one let’s use it!


More experiments with your galvanometer

You will need:


  • Your handy galvanometer
  • The strongest magnet you own
  • Another 2 feet or more of wire
  • Toilet paper or paper towel tube

1. Take your new piece of wire and remove about an inch of insulation from both ends of the wire.


2. Wrap this wire tightly and carefully around the end of the paper towel tube. Do as many wraps as you can while still leaving about 4 inches of wire on both sides of the coil. You may want to put a piece of tape on the coil to keep it from unwinding. Pull the coil from the paper towel tube, keeping the coil tightly wrapped.


3. Hook up your new coil with your galvanometer. One wire of the coil should be connected to one wire of the galvanometer and the other wire should be connected to the other end of the galvanometer.


4. Now move your magnet in and out of the the coil. Can you see the compass move? Does a stronger or weaker magnet make the compass move more? Does it matter how fast you move the magnet in and out of the coil?


Taa Daa!!! Ladies and gentlemen you just made electricity!!!!! You also just recreated one of the most important scientific discoveries of all time. One story about this discovery, goes like this:


A science teacher doing a demonstration for his students (can you see why I like this story) noticed that as he moved a magnet, he caused one of his instruments to register the flow of electricity. He experimented a bit further with this and noticed that a moving magnetic field can actually create electrical current. Thus tying the magnetism and the electricity together. Before that, they were seen as two completely different phenomena!


Now we know, that you can’t have an electric field without a magnetic field. You also cannot have a moving magnetic field, without causing electricity in objects that electrons can move in (like wires). Moving electrons create a magnetic field and moving magnetic fields can create electric currents.


“So, if I just made electricity, can I power a light bulb by moving a magnet around?” Yes, if you moved that magnet back and forth fast enough you could power a light bulb. However, by fast enough, I mean like 1000 times a second or more! If you had a stronger magnet, or many more coils in your wire, then you could make a greater amount of electricity each time you moved the magnet through the wire.


Believe it or not, most of the electricity you use comes from moving magnets around coils of wire! Electrical power plants either spin HUGE coils of wire around very powerful magnets or they spin very powerful magnets around HUGE coils of wire. The electricity to power your computer, your lights, your air conditioning, your radio or whatever, comes from spinning magnets or wires!


“But what about all those nuclear and coal power plants I hear about all the time?” Good question. Do you know what that nuclear and coal stuff does? It gets really hot. When it gets really hot, it boils water. When it boils water, it makes steam and do you know what the steam does? It causes giant wheels to turn. Guess what’s on those giant wheels. That’s right, a huge coil of wire or very powerful magnets! Coal and nuclear energy basically do little more than boil water. With the exception of solar energy almost all electrical production comes from something huge spinning really fast!


Exercises


  1. Why didn’t the coil of wire work when it wasn’t hooked up to a battery? What does the battery do to the coil of wire?
  2. How does a moving magnet make electricity?
  3. What makes the compass needle deflect in the second coil?
  4. Does a stronger or weaker magnet make the compass move more?
  5. Does it matter how fast you move the magnet in and out of the coil?

Click here to go to your next lesson on Conductivity!

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Conductivity

Monday November 24, 2014

switch-zoomMake yourself a grab bag of fun things to test: copper pieces (nails or pipe pieces), zinc washers, pipe cleaners, Mylar, aluminum foil, pennies, nickels, keys, film canisters, paper clips, load stones (magnetic rock), other rocks, and just about anything else in the back of your desk drawer.


Certain materials conduct electricity better than others. Silver, for example, is one of the best electrical conductors on the planet, followed closely by copper and gold. Most scientists use gold contacts because, unlike silver and copper, gold does not tarnish (oxidize) as easily. Gold is a soft metal and wears away much more easily than others, but since most circuits are built for the short term (less than 50 years of use), the loss of material is unnoticeable.
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Modify your basic LED circuit into a Conductivity Circuit by removing one clip lead from the battery and inserting a third clip lead to the battery terminal. The two free ends are your new clips to put things in from the grab bag. Try zippers, metal buttons, barrettes, water from a fountain, the fountain itself, bike racks, locks, doorknobs, unpainted benches… you get the idea!


Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 3 alligator wires
  • LEDs (any you choose is fine)
  • paper clip
  • penny
  • other metal objects around your house (zippers, chairs, etc…)


Why does metal conduct electricity?

Why does metal, not plastic, conduct electricity? Imagine you have a garden hose with water flowing through it. The hose is like the metal wire, and the water is like the electric current. Trying to run electricity through plastic is like filling your hose with cement. It’s just the nature of the material.



Download Student Worksheet & Exercises


Exercises


  1.       Name six materials that are electrically conductive.
  2.        What kinds of materials are conductors and insulators?
  3.      Can you convert an insulator into a conductor? How?
  4.        Name four instances when insulators are a bad idea to have around.
  5.      When are insulators essential to have?

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Click here to go to your next lesson on requirements for a circuit!

Requirements for a Circuit

Monday November 24, 2014

You need two important things for an electric circuit: first you need a closed conductive path that goes from the positive to the negative terminal of the battery. When I teach this activity to kids, there’s always a couple that try to light up the LED just using the LED and wires (they forget about the battery completely!) You always need a power source in the circuit in order for charges to flow. The charges only flow through something that conducts electricity. Sometimes kids forget about the conductive part, and just try to touch the plastic coating on the wires to the LED and are frustrated when it doesn’t work right. It must be a closed conductive loop.


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The second thing is that there needs to be an electric potential difference across the two ends of the circuit. (You can think of the ends as the ends that are connected to the battery.) Because it takes energy to move the charge from a low to a high potential (remember how it takes energy to go up a flight of stairs?), there needs to be something that supplies the charges with the energy they need to go from a low to a high electric potential so then they can move through the circuit on their own. As the charge moves though the circuit, it loses energy until it reaches the negative terminal at zero energy. Then the battery gives that charge energy and it moves back up to the positive terminal at high energy and does it all over again. The battery pumps up the charges and creates an electric potential difference across the two ends of the circuit.


In your house, the electric outlet that you plug appliances and lamps into is the electric potential difference. The three holes in the outlet are hot, neutral, and ground.


The hot terminal is the smaller one on the upper right, and this has the highest potential. Neutral is the larger one on the upper left, and it is the return path for current (and should always be considered to be high potential. It’s unfortunately pretty common for hot and neutral wiring to be reversed, because the outlet still works if it is.) Ground is the roundish one at the bottom and is there for safety. Ground and neutral are connected together back at the box, and they give electricity the quickest and simplest way back to the low potential.  An ungrounded device (including extension cords) can be dangerous if there’s no path to ground except through you.


The electrical outlet in US homes supplies 110-120 volts of voltage and 15-20 amps of current. On the other hand, a AA battery has 1.5 volts and about 50 mA (that;s 0.050 amps), depending on the type of battery and what kind of load you are putting on it.


And just in case you’re considering poking something into the outlet, over 4,000 people every year are in the emergency room for injuries that have to do with sticking something other than a plug into an electrical outlet, about one third of them are kids under 18 years old. And those are just the ones you made it to the hospital… some were not as lucky and never made it at all. The current can kill you because you’re made up mostly of water, which makes it a really good conductor of electricity. Electricity is always looking for the easiest way to ground, and though you is one of those ways and the amount of current that passes through you is enough to stop your heart and damage your cells. Bottom line: the only thing you should put into an outlet is a plug.


Click here to go to your next lesson on the water analogy!

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Water Analogy 

Monday November 24, 2014

This is a recording of a recent live robotics teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!


We’ll cover topics in electricity, magnetism, electrical charges, robot construction, sensors and more by building several projects together. For now, just watch the video and if you already have the materials to build the projects, feel free to do it along with me. If not, don’t worry… we’ll get to these projects soon in the course.


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Materials:


  • AA battery case (Jameco 216081)
  • Two AA batteries for your battery case**
  • A couple of LEDs (You can use any under 3V, but if you need recommendations, try Jameco 2-lead LEDs or 3-lead LEDs)
  • Set of 10 alligator wires (Jameco 10444)
  • One or two 1.5-3V DC motors (Jameco 231925)
  • Index card
  • 6 brass fasteners
  • Two large paper clips
  • One foam block (2” cube or larger)
  • 1 wooden clothespin
  • 10 wooden skewers
  • Drill & bit the size of the motor shaft diameter
  • Hot glue gun, razor and adult assistant
  • OPTIONAL: Buzzer (Jameco 24872)

**Note about batteries: The cheap dollar-store kind labeled “Heavy Duty” are recommended. Do not use alkaline batteries like “Duracell” or “Energizer” for your experiments with us during this class. (We’ll explain during the class.)



Download the worksheet for this teleclass HERE.


Key Concepts

A robot not only moves but it can also interact with its environment and it does that by using sensors, like light detectors that can see light, you can have motion detectors that can sense movement, touch sensors, pressure sensors, infrared light sensors, proximity sensors, water detectors, spit sensors, detecting all different kinds of stuff!


Robots need electricity to make the motors move, the LEDs light up, the buzzers to sound, and more. When you move electrons around, that’s what creates the electricity. When you rub a balloon on your head for example, you’re picking off the electrons from the atoms in your hair and sticking them on the balloon. There’s a static charge on your head due to the extra electrons.


The electrons have a negative charge, and so just like the north and south poles of a magnet attract each other, the negative charge of the electron is attracted to positive charges. That’s why your batteries have plus and minus signs on them. Electricity is when the electric charge is moving around inside the wires in the circuit.


Current is measured in amps, and is a measure of how much charge is flowing through the circuit at a certain point. We use the letter I  to mean current when we’re doing calculations on paper, and it’s important to remember that current is like velocity in that it’s a rate.Just like velocity is the change in position per unit time, current is the amount of charge per unit time: I = Q/t. This means that one amphere (amp) is one coulomb per second.


Click here to go to your next lesson on Franklin’s Mistake!

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Franklin’s Mistake

Monday November 24, 2014

If this next part is too confusing, just skip over it. I did want to let you know (for those of you who have spotted it already) that there’s a big problem with the positive test charge model we’ve been using. Well, it’s kind of a problem, but not really a big one once you get used to the idea.


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When we determined which one is the high and low potential (the plus and minus on a battery), we assumed that the test charge was positive. The particles that move charge through the wires are actually negatively, not positively, charged. We’ve been dealing with just positive charges so far, and now we’re going to mix things up a bit since electrons are in fact, negative. This means that current actually goes from the negative terminal to the positive terminal because that charge is being carried by electrons. Note that charge carriers don’t have to be electrons (they can also be positively charged or both traveling simultaneously in opposite directions!)


It was actually one of Ben Franklin’s not-so-great moments when he arbitrarily assigned the direction of electric current the way we think about it today, which is going from the positive to the negative terminal. Electrons actually move in  the opposite direction! BUT in the real world, we all think about current flowing from plus to minus (even though in reality its the opposite direction). Just file it away in your mind in case it ever comes up (which it probably won’t) that you would need to know the actual direction the electrons are moving in a circuit (which most people don’t need to know or care about).


Click here to go to your next lesson on learning about charge carriers!

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Charge Carriers are Not Used Up

Monday November 24, 2014

In electric circuits, the charge carriers are electrons, which are already inside the wire itself. The battery doesn’t add extra electrons to the circuit to make it go… the electrons inside the wires are already there. The battery provides an electric potential difference that signals the electrons to start moving, and this signal travels at the speed of light (or close to it), and then the electrons start moving (quite a bit slower than the speed of light). This means that electrons don’t have to start at the battery and them go all the way to the light before the light bulb lights up, because the electrons inside the filament itself are the ones that start glowing when they get the signal to start moving.


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All electrons everywhere start moving as soon as they get that signal from the battery, like like water flowing in the hose that we saw in the teleclass video. The electrons themselves don’t get used up, but rather the energy carried by the electrons is transformed to other forms of energy (including heat, light, sound, motion, etc.). The charge itself doesn’t transform or get used up, just the energy itself. Kids use up their energy as they run, play, and jump , and need to refuel before they can go back in the afternoon to the playground. The kids don’t get used up, but rather the energy the kid is carrying is being transformed from chemical energy int the food to motion energy , and needs to be replenished when the kid runs out of energy.


Click here to go to your next lesson on Switches!

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Switches

Monday November 24, 2014

knifeswitchWhen you turn on a switch, it’s difficult to really see what’s going on… which is why we make our own from paperclips, brass fasteners, and index cards.


Kids can see the circuit on both sides of the card, so it makes sense why it works (especially after doing ‘Conductivity Testers’).


SPST stands for Single Pole, Single Throw, which means that the switch turns on only one circuit at a time. This is a great switch for one of the robots we’ll be making soon, as it only needs one motor to turn on and off.
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Think of this switch like a train track. When you throw the switches one way, the train (electrons) can race around the track at top speed. When you turn the switch to the OFF position, it’s like a bridge collapse for the train – there’s no way for the electrons to jump across from the brass fastener to the paper clip. When you switch it to the ON position (both sides), you’ve rebuilt the bridges for the train (electrons).


Troubleshooting: The two tabs on the back of the motor are the places to clip in the power from the battery pack. Since these motors spin quickly and the shaft is tiny, add a piece of tape to the shaft to see the spinning action more clearly.


Kids can make their own switches so they can trace the path the electricity takes with a finger. See what you think about this SPST:


Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 3 alligator wires
  • index card
  • 2 brass fasteners
  • paper clips
  • buzzer, motor, or LED


Download Student Worksheet & Exercises


Exercises


  1.  If you want to reverse the spin direction of a motor without using a switch, what can you do?
  2.  A simple switch can be made out of what kinds of materials?
  3.  How would you make your SPST switch an NC (normally closed) switch?
  4.  How did you have to connect your circuit in order for both the LED and motor to work at the  same time? Draw it here:
  5.  Draw a picture of your experiment that explains how the SPST switch works, and show how      electricity flows through your circuit:

Extra Credit (for students who have completed Part 3):


  1. Draw a picture of your experiment that explains how the DPDT switch works in your circuit and show how to wire up the circuit.

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 Click here to go to your next lesson on Electric Circuit Loads!

Loads in a Circuit

Monday November 24, 2014

Imagine you have two magnets. Glue one magnet on an imaginary record player (or a ‘lazy susan’ turntable) and hold the other magnet in your hand. What happens when you bring your hand close to the turntable magnet and bring the north sides together?


The magnet should repel and move, and since it’s on a turntable, it will circle out of the way. Now flip your hand over so you have the south facing the turntable. Notice how the turntable magnet is attracted to yours and rotates toward your hand. Just as it reaches your hand, flip it again to reveal the north side. Now the glued turntable magnet pushes away into another circle as you flip your magnet over again to attract it back to you. Imagine if you could time this well enough to get the turntable magnet to make a complete circle over and over again… that’s how a motor works!


After you get the buzzer and the light or LED to work, try spinning a DC motor:


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Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 2 alligator wires
  • 1.5-3V DC motor
  • optional: propeller


Click here to go to your next lesson on Power!

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Power

Monday November 24, 2014

We’re going to define power in an electric circuit as the rate tat electrical energy is used by the load (or supplied by the source). Power is then equal to the work done by the charge per unit time, or said another way, the rate that the charge changes its energy (whether it’s lost or gained).


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For a battery, the charge gains energy so it’s a positive quantity, and in the devices in the circuit (the load), energy is lost, so the change is negative. Power is measured in Watts (W), and 1 watt delivers 1 joule of energy every second.


1 Watt = 1 Joule / second


An incandescent light bulb might have a 100 Watt rating stamped on it, which means 100 joules of energy is being delivered every second to the light bulb. A 15 watt night light gets 15 joules of energy every second.


Have you ever seen an electric bill? They don’t charge you by the “watt”, but by the “kWhr” or “kWh”, which is a kilowatt-hour. (A kilowatt is 1,000 watts.) A kWhr is a unit of power per unit time, which means it’s a measure of energy. Your electric bill is a bill for energy, not power.


Click here to go to your next lesson on Making Sense of it All!

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Making Sense of It All

Monday November 24, 2014

A lot of people don’t understand electricity, but they use it all the time. Normally I’d agree with this approach: know enough so you can make good use of it, and for the most part, I’ve done that in this course. However, because this is such an advanced course specifically in electricity, I want to make sure we’ve busted the main myths out there around electricity, Over the years, I’ve heard many different ideas folks have about electricity, and at some level, it’s really not their fault for these misconceptions because they are still so popular.


It’s important as a scientist that you question not only what you know but how you know what you know. This will lead you to the truth about how things work, and not just what most people think the reason is (which isn’t usually correct). Here are a couple of mainstream ones that still persist today:
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  1. If a battery is dead, it is out of charge, and you have to recharge it so it works.
  2. The current that flows through the circuit starts in the battery.
  3. The utility company supplies electrons to your house through the outlet.
  4. Electrons move at light speed in the circuit.
  5. Electrons get used up as they move through the circuit.
  6. Benjamin Franklin invented the light bulb.

Note that all of these above are false! Your test for today is to make sure you understand why that is for each one. Go back and re-read this section and the previous sections if you need more help. Here’s a couple of hints if you need it:



To review, a battery provides energy move a charge from a low potential to a high potential, and the charge came from the wires and electrical components inside the circuit itself. The charge is carried by electrons in the metal components. Charge moves really slow (about 1 meter per hour), but the signal to moves travels near the speed of light. Charge moves through the circuit at the same rate everywhere in the circuit (charge doesn’t build up in a circuit that is closed and conducting properly). A circuit is really an energy transforming device that takes chemical energy from the battery and transformed it to electrical energy in the circuit and transforms that into different kinds of energy like motion, heat, light, and sound.


Click here to go to your next lesson on Electric Circuits!

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Electric fields are like Gravitational Fields

Monday November 17, 2014
Electric fields are like gravitational fields in a couple of important ways. They both have forces that act at a distance. Remember with the gravitational field, in order to walk up stairs, you are doing work (exerting a force) against the pull of gravity. Your body naturally wants to be at the ground level, and it takes work to get it up a flight of stairs. You move from a lower potential energy to a higher potential energy as you walk up those stairs. When you walk up the stairs, you are adding gravitational potential energy to your body. And it doesn't matter how wacky the staircase is... it can have curves, dips, switchbacks, and more... but it's only the beginning and end points that we care about when calculating the gravitational potential energy.Electric Potential Difference.

[am4show have='p9;p58;' guest_error='Guest error message' user_error='User error message' ] Electric fields work the same way, except with charges. In order to move a charge in an electric field against the way it naturally wants to go, you have to do work on it by applying an external force. This work done adds to the potential energy of the charge in the form of electrical potential energy. And it doesn't matter what the path is that the charge takes between the two points... it's only the beginning and ends points that matter. Both the electrostatic and gravitational forces are conservative forces.

When you walk up a flight of stairs, the amount of gravitational potential energy stored in your body depends on two things: your mass and the height of the stairs. A person twice your size will have twice the potential energy, as will you if you walk up two flights of stairs instead of one. If we divide the gravitational potential energy term by mass, then we can find the gravitational potential per kg for an object that doesn't care how massive an object is and only cares where it's located.

So the bottom line is that if you move a charged particle in an electric field, the potential energy also changes. Moving it in against the direction of an electric field would be like climbing up a flight of stairs, because you're going against the nature of gravity and it requires work to get up those stairs. Going down a flight of stairs equates to losing potential energy, the same which holds true with a charged particle moving with the nature of the electric field (it will also lost electric potential energy).

Click to go to your next lesson on Electric Potential!

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Electric Potential

Monday November 17, 2014

Now before you roll your eyes, let me explain that this is how we specify the electric potential energy. We want it to be based only on location, so it’s defined this way:


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Electric Potential (V) = Potential Energy (PE) / charge (q)


The electric potential energy of a charged particle depends on two things: the electric charge, and where it is in the electric field (how close to the source is it?). A larger charge on the particle means there’s more repulsive force that shows up when you move it against the nature of the electric field, which means more work is involved to move that charge. If you plunked down two objects, one with twice the charge of the other, into an electric field, the one with twice the charge experiences twice the force (and also have twice the potential energy). It has a higher electric potential when it’s held close to a source of the same charge, and a lower potential when it’s moved further away.



Click here to go to your next lesson on making a magnesium battery!

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Magnesium Battery

Monday November 17, 2014

Magnesium is one of the most common elements in the Earth’s crust. This alkaline earth metal is silvery white, and soft. As you perform this lab, think about why magnesium is used in emergency flares and fireworks. Farmers use it in fertilizers, pharmacists use it in laxatives and antacids, and engineers mix it with aluminum to create the BMW N52 6-cylinder magnesium engine block. Photographers used to use magnesium powder in the camera’s flash before xenon bulbs were available.


Most folks, however, equate magnesium with a burning white flame. Magnesium fires burn too hot to be extinguished using water, so most firefighters use sand or graphite.


We’re going to learn how to (safely) ignite a piece of magnesium in the first experiment, and next how to get energy from it by using it in a battery in the second experiment. Are you ready?


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Materials:


  • magnesium strip (MSDS)
  • matches with adult help
  • tile or concrete surface (something non-flammable)
  • gloves, goggles

Burning magnesium produces ultraviolet light. This isn’t good for your eyes, and the brightness of the flame is another danger for your eyes. Avoid looking directly into the flame.


Burning magnesium is so hot that if it gets on your skin it will burn to it and not come off. As difficult as burning magnesium is to put out, avoid letting the burning metal come in contact with you or anything else that might catch fire.


As explained later in this lab, magnesium burns in carbon dioxide. Therefore, a CO2 fire extinguisher won’t work to put it out. Water won’t work, CO2 won’t work. It takes a dry chemical fire extinguisher to put it out, or just wait for it to burn up completely on its own.


Magnesium is a metal, and in this experiment, you’ll find that some metals can burn. The magnesium in this first experiment combines with the oxygen in the air to produce a highly exothermic reaction (gives off heat and light). The ash left from this experiment is magnesium oxide:


2Mg (s) + O2 (g) –> 2Mg O (s)


Not all the magnesium from this experiment turned directly into the ash on the table – some of it transformed into the smoke that escaped into the air.


Caution: Do NOT look directly at the white flame (which also contains UV), and do NOT inhale the smoke from this experiment!



Download Student Worksheet & Exercises


Here’s what’s going on in this experiment:


As you burn your magnesium, you will get your very own fireworks show….a little one, but still cool.


2Mg + O2 –> 2MgO


Magnesium burned in oxygen yields magnesium oxide. Because the temperature of burning magnesium is so high, small amounts of magnesium react with nitrogen in the air and produce magnesium nitride.


3Mg + N2 –> 2Mg3N2


Magnesium plus nitrogen yield magnesium nitride. Magnesium will also burn in a beaker of dry ice instead of in air (oxygen).


2Mg + CO2 –> 2MgO + C


Magnesium burned in carbon dioxide yields magnesium oxide and carbon (ash, charcoal, etc.)


Cleanup: Rinse off and pat dry the rest of the magnesium strip.


Storage: Place everything back in its proper place in your chemistry set.


Disposal: Dispose of all solid waste in the garbage.


Magnesium Battery

Now let’s see how to make a battery using magnesium, table salt, copper wire, and sodium hydrogen sulfate (AKA sodium bisulfate).


Materials:


  • magnesium strip
  • test tube and rack
  • light bulb (from a flashlight)
  • 2 pieces of wire
  • measuring cup of water
  • salt (sodium chloride)
  • copper wire (no insulation, solid core)
  • measuring spoon
  • sodium hydrogen sulfate (NaHSO4) (MSDS) Sodium hydrogen sulfate is very toxic. Respect it, handle it carefully and responsibly. Do not take it for granted.
  • gloves, goggles

NOTE: Be very careful when handling the sodium hydrogen sulfate – it’s highly corrosive and dangerous when wet. Handle this chemical only with gloves, and be sure to read over the MSDS before using.


We’re going to do another electrolysis experiment, but this time using magnesium instead of zinc. In the previous electrolysis experiment, we used electrical energy to start a chemical reaction, but this time we’re going to use chemical energy to generate electricity. Using two electrodes, magnesium and copper, we can create a voltaic cell.


TIP: Use sandpaper to scuff up the surfaces of the copper and magnesium so they are fresh and oxide-free for this experiment. And do this experiment in a DARK room.


How cool is it to generate electricity from a few strips of metal and salt water? Pretty neat! This is the way carbon-core batteries work (the super-cheap brands labeled ‘Heavy Duty’ are carbon-zinc or ‘dry cell’ batteries). However, in dry cell batteries scientists use a crumbly paste instead of a watery solution (hence the name) by mixing in additives.


In this chemical reaction, when the magnesium metal enters into the solution, it leaves 2 electrons behind and turns into a magnesium ion:


Oxidation: Mg (s) –> Mg2+(aq) + 2e–


The magnesium strip takes on a negative charge (cathode), and the copper strip takes on a positive charge (anode). The copper strip snatches up the electrons:


Reduction: Cu2+(aq) + 2e– –> Cu (s)


and you have a flow of electrons that run through the wire from surplus (cathode) to shortage (anode), which lights up the bulb.


Note: You can substitute a zinc strip or aluminum strip for the magnesium strip and a carbon rod (from a pencil) for the copper wire.


Going further: You can expand on this experiment by substituting copper sulfate and a salt bridge to make a voltaic cell from two half-cells in Experiment 16.5 of the Illustrated Guide to Home Chemistry Experiments.


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Click here to go to your next lesson on how to make a fruit battery.

Fruit Battery

Monday November 17, 2014

This experiment shows how a battery works using electrochemistry. The copper electrons are chemically reacting with the lemon juice, which is a weak acid, to form copper ions (cathode, or positive electrode) and bubbles of hydrogen.


These copper ions interact with the zinc electrode (negative electrode, or anode) to form zinc ions. The difference in electrical charge (potential) on these two plates causes a voltage.


Materials:


  • one zinc and copper strip
  • two alligator wires
  • digital multimeter
  • one fresh large lemon or other fruit

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Download Student Worksheet & Exercises


Roll and squish the lemon around in your hand so you break up the membranes inside, without breaking the skin or leaking any juice. If you’re using non-membrane foods, such as an apple or potato, you are all ready to go.


Insert the copper and zinc strips into the lemon, making sure they do not contact each other inside. Clip one test wire to each metal strip using alligator wires to connect to the digital multimeter. Read and record your results.


What happens when you gently squeeze the lemon? Does the voltage vary over time?


You can try potatoes, apples, or any other fruit or vegetable containing acid or other electrolytes. You can use a galvanized nail and a copper penny (preferably minted before 1982) for additional electrodes.


If you want to light a light bulb, try using a low-voltage LED in the 1.7V or lower hooked up to several lemons connected in series. For comparison, you’ll need about 557 lemons to light a standard flashlight bulb.


What’s going on?


The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.


When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.


Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.


Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.


You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.


Exercises


  1.  What kinds of fruit make the best batteries?
  2.  What happens if you put one electrode in one fruit and one electrode in another?
  3.  What happens if you stick multiple electrode pairs around a piece of fruit, and connect them in series (zinc to copper to zinc to copper to zinc…etc.) and measure the voltage at the start and end electrodes?

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Click here to go to your next lesson on learning how a battery can store energy.

Can a Battery Store Energy?

Monday November 17, 2014

Why is one end designated as the “high potential” end? If you watch a positive charge move from the negative terminal to the positive terminal, it requires work to move this charge (the positive charge experiences a repulsive force as it moves closer to the positive terminal), which increases the potential energy of the charge because you’re moving a positive charge against the electric field.
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Click here to go to your next lesson on learning how to make a solar battery.

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Solar Battery

Monday November 17, 2014

Moving the positive charge from the positive to negative terminal would be with the electric field, so the charge would experience a decrease in potential energy as it moved through an external circuit. (You’ve noticed that we’re only talking about positive test charges here in order to determine which end of the battery is high and which end is low.) This is a really neat experiment on how to make your own solar battery. If you don’t have time or copper flashing for this one, you can just skip doing it but be sure to watch it just for fun…
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Click here to go to your next lesson on making a salty battery.

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Salty Battery

Monday November 17, 2014

Using ocean water (or make your own with salt and water), you can generate enough power to light up your LEDs, sound your buzzers, and turn a motor shaft. We’ll be testing out a number of different materials such as copper, aluminum, brass, iron, silver, zinc, and graphite to find out which works best for your solution.


This project builds on the fruit battery we made in Unit 8. This experiment is for advanced students.


The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.


When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.


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Here’s what you need:


  • water
  • salt
  • vinegar (distilled white)
  • bleach IMPORTANT: WEAR GOGGLES!
  • glass container (like a cleaned out jam jar)
  • electrodes
  • real silverware (not stainless)
  • shiny nail (galvanized)
  • large paper clip
  • dull nail (iron)
  • wood screws (brass)
  • copper pennies minted before 1982 (or a short section of copper pipe)
  • graphite from inside a pencil (use a mechanical pencil refill)
  • 2 alligator wires
  • digital multimeter


Download Student Worksheet & Exercises


Here’s what you do:


  1. Fill a cup with water, adding a teaspoon of salt, a teaspoon of distilled white vinegar, and a few drops of bleach.  NOTE: BE very careful with bleach!  Cap it and store as soon as you’ve added it to the cup.
  2. Find two of the following materials: copper*, aluminum*, brass, iron, silver, zinc, graphite (* indicates the ones that are easiest to start with – use a copper penny and a piece of aluminum foil). Attach an alligator clip lead to each one and dunk into your cup. Make sure these two metals DO NOT TOUCH in the solution.
  3. You’ve just made a battery!  Test it with your digital volt meter and make a note of the voltage reading. Connect the multimeter in series to read the current (remove a clip from the metal and clip it to one test probe, and attach the other test probe to the metal. Make sure you’re reading AMPS, not VOLTS when you note the reading for current).
  4. Test out different combinations of materials and note which gives the highest voltage reading for you. Is it enough to light an LED? Buzzer? Motor?  What if you made two of these and connected them in series? Three? Four?

Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.


Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.


You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.


Exercises


  1. Which combination gives the highest voltage?
  2. What happens if you use two strips of the same material?
  3. What would happen if we used non-metal strips?

Click here to go to your next lesson on a college level electricity class!

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Taking A College Class in Electricity

Monday November 17, 2014

Have you ever wondered what college will be like? Here’s a video from a professor at MIT on electrostatics, specifically the electric field and the electric potential. It’s a full class lecture, so don’t worry if you get a little lost with the calculations on the chalkboard. Just sit back and enjoy watching learning from someone other than me (Aurora) so you get more than one perspective on the subject.




Click here to go to your next lesson on voltage.

Voltage

Monday November 17, 2014

Electric potential is defined as the amount of potential energy per charge. Watch this next video and see if you can quickly determine the work done on the charge and where the electric potential is the greatest…


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So to put it all together (because now we’re about to make a big leap): what we’ve figured out so far is that if you have a charge that has a large amount of electric potential energy in a specific location, that location has a high potential. (And the opposite is also true for low potential.)  This means you can have an electric potential difference between two locations. And that’s what drives the entire electric industry. That’s exactly why we have computers, power lines, cell phones, and lights… and so much more!


The electric potential difference is written like this: ΔV (“delta” V), and it’s the difference between the final and initial locations when you do work on a charge to move it (and thus change its potential energy). The electric potential difference is work per unit charge, or the change in potential energy per unit charge.



where V is the electric potential, and Wfi is the work done by the electric field on the positive test charge as it moves from point i to f (so this can be positive, negative, or zero). The units are a “Joule per Coulomb”, which is defined to be 1 Volt.


Click here to go to your next lesson on balloons rising in the air.

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Point Charge

Monday November 17, 2014

Imagine you have a positive test charge in an electric field and you move it from one point to another. When you move it, the charge against the electric field, you have to do work on it using an external force, like your hand pushing it along the path. The work done by your hand on the charge will increase the potential energy and also cause a difference in the electric potential between the start and finish locations. If the electric potential difference between the start and finish is 10 volts, then one Coulomb of charge will increase by 10 Joules of potential energy when you push the charge from start to finish. This is what voltage is.


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Click here to go to your next lesson on what’s inside gold.

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Skiing Down a Mountain

Monday November 17, 2014

Now imagine a simple circuit that uses a light bulb (or LED) and a battery. The battery provides the energy to do work on the charges to move it from the negative to the positive terminal. Once the charge is at the high potential (the plus side of the battery), it’s like taking a chair lift to the top of a mountain… it is now ready to ski down the mountain with little to no effort. So once the charge is at the high potential terminal, it naturally flows through the wires to the low potential terminal. The ski lift is doing work to get you up the mountain against the nature of the gravitational field the same way the battery is doing work on the electric charge moving it from a low to high potential.
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The battery is the internal circuit, because energy is given to the charge. The external circuit is the part where the charge loses energy by moving along the wires and lighting up LEDs, making buzzers sound, turning motors, etc. Each element in the circuit takes energy from the charge (even the wire itself) and transforms it into something useful or not. Light, sound, motion are all useful forms of energy. The heat coming from an incandescent light bulb would be non-useful thermal energy.



As the charge moves through a device, it starts out at a higher energy than it leaves the device with, so there’s a voltage drop across that circuit element. The charge returns to the low potential side of the battery at zero volts and is ready to be pumped back up to the high voltage positive terminal.


Click here to go to your next lesson on reviewing the electric potential difference.

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Review on Electric Potential Difference

Monday November 17, 2014

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To review, an electron moving in an electric field would change the potential energy of the electron, and the way it moves through the field determines whether it gains or loses energy. When you turn on a flashlight, the battery supplies energy to move the charge through the battery and makes an electric potential difference so the charge can then have enough energy to move through the wires and light bulb of your flashlight. The battery doesn’t add protons, neutrons, or electrons to the circuit. The electrons that move are already in the wire itself. Charge doesn’t get used up in the circuit, only energy is used up.



Click here to go to your next lesson on the Uranium Atom

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Electric Fields

Wednesday November 5, 2014

Now you understand how scuffing along a carpet in socks builds up electrons on the body, and how this negative electric charge affects other things (like your cat) when you reach a finger out to touch them. You also know how opposite charges attract and like charges repel, and the difference between balanced charges and unbalanced charges.


We’re going to dive into studying force fields. You may wonder what force fields have to do with a serious examination of physics like the one in this lesson. You probably consider force fields to be something you might hear about in a science fiction scene such as…


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Meanwhile, in section 27B of the Horse Crab Galaxy, First Mate Fred frets, “Captain Clyde! the force field is too strong. Our ship will never make it through.” “Never worry First Mate Fred!” exclaims Captain Clyde calmly. “I’ve increased power to the neutron-frapters so we will be just fine.” “Captain Clyde, that’s genius. You’re my hero!” First Mate Fred fawns.  


Truthfully, however, force fields aren’t just something for science fiction writers. They are actually a very real and very mysterious part of the world in which you live. So, what is a force field? Well, I can’t tell you. To be honest, nobody can.


There’s quite a bit that is still unknown about how they work. A force field is a strange area that surrounds an object. That field can push or pull other objects that wander into its area. Force fields can be extremely tiny or larger than our solar system. There are gravitational fields, magnetic fields, electric fields, and electromagnetic fields.



Click here to go to next lesson on Maxwell’s Third Equation.

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Maxwell’s Third Equation

Wednesday November 5, 2014

Overall, Maxwell’s four equations describe the fundamentals of electricity and magnetism. However, one look at these mathematical equations can make a high school student run screaming from the room, so we’re not going to dive into the sophisticated mathematics of the equations themselves, but rather what they really tell us about the relationships between the electric and magnetic fields.


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Gravitational forces, magnetic forces, and electric forces are all action-at-a-distance forces (sometimes called field forces), meaning objects can interact even they are not touching each other.  The Earth and a ball are attracted to each other, even when the ball is tossed high up in the air. Two magnets can push against each other even when they are not touching. Same thing with two electrons: the negative charge on the electrons create a repulsive force that pushes on each electron.


A way to picture a force field is to imagine an invisible bubble that surrounds a gizmo. If some other object enters that bubble, that object will be pushed or pulled by an invisible force that is caused by the gizmo. That’s pretty bizarre to think about isn’t it?


Well,  not really. If you’ve ever been around a baby, you know that you can detect a diaper change without even peeking in there. The baby created a stinky field. It’s an invisible area that you can detect around the baby which increases in stinky-ness the closer to the baby you get. On the other hand, if you can imagine someone making your favorite meal and you walk into the house after a hard day, you enter into a wonderfully aromatic house filled with your favorite smells, you’re entering another field that you can detect, and the closer you get to the stove, the more intense the field becomes.


Click here to go to next lesson on Electric Field Lines.

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Electric Field Lines

Wednesday November 5, 2014

A field changes the nature of the space surround the thing producing the field. A magnet produces a magnetic field which changes the nature of the space around it so that other magnets and magnetic objects are now influenced by it. Some magnetic fields (and other fields) are stronger than others, and now we’re going to learn how to measure the field strength of electric fields.


The electric field is a vector (it has magnitude and direction), and this is how you do it:


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Click here to go to next lesson on Electric Fields.

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Electric Fields

Wednesday November 5, 2014

Michael Faraday was the first to come up with the idea about electric fields. He thought of the space around a charged object as being filled with lines of force. He was trying to figure out a pattern that represented what the electric field looked like by imagining the electric field as a bubble around a charged object and how it would interact with another object that enters into that bubble. This is a little different than imagining a charge interacting with a charge. There’s a field interaction between the two charges. Every charge creates a bubble around it that in turn, affects the space within that bubble.


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Click here to go to next lesson on Using Spices to Detect Field Lines.

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Using Spices to Detect Field Lines

Wednesday November 5, 2014

Have you wrapped your mind around static electricity yet? You should understand by now how scuffing along a carpet in socks builds up electrons, which eventually jump off in a flurry known as a spark. And you also probably know a bit about magnets and how magnets have north and south poles AND a magnetic field (more on this later). Did you also know that electrical charges have an electrical field, just like magnets do?


It’s easy to visualize a magnetic field, because you’ve seen the iron filings line up from pole to pole. But did you know that you can do a similar experiment with electric fields?


Here’s what you need:


  • dried dill (spice)
  • vegetable or mineral oil
  • 2 alligator wires
  • static electricity source (watch video first!)

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Download Student Worksheet & Exercises


Here’s what you do:


1. Fill a saucer with vegetable or mineral oil.
2. Sprinkle small seeds or spices on top, such as caraway, anise, or dill (this one works best).
3. Build up an electric charge by either rubbing a balloon on your head, rubbing a PVC pipe with a wool sweater or mittens, or your favorite way to build up to a spark.
4. Bring the charged object near the oil – what happened to the spices?
5. Does it matter which end of the balloon/pipe/etc you hold near the oil? What if you move it a bit near the dish?
6. Stir the dill into the oil. Bring a charged object near and watch the dill spring up to touch the rod.


Troubleshooting:
If your dill isn’t moving at all, your object may be too ‘dirty’ (e.g. have too much oil from your fingers) on it to hold a charge. Clean it with rubbing alcohol after you use soap and water, and you should see better results.


What’s going on?
The dill/caraway/anise are all shaped like rods, which move to line up in the field (which is why round particles like cinnamon and pepper don’t work as well). The dill has a balance of charges – both plus and minus – and when you bring a charged object close, the negative charges in the dill are attracted to the balloon but the positive charges are repelled, so one side of the dill becomes minus and the other plus. Since the dill is free to move in the liquid, it lines up in the electric field to indicate the charge direction.


If you move the balloon just right, the attractive electrical charge will pull the lightweight dill right up out of the oil and onto the balloon. Have fun!


Exercises


  1. What happened when you brought a charged balloon near the dill?
  2. What side of the dill was attracted to the balloon?
  3. What happened when you brought two negative charges near the dill?
  4. Were you able to make the dill come out of the liquid and onto the balloon without touching the oil?

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Click here to go to next lesson on Weird Shapes and Field Lines.

Weird Shapes and Field Lines

Wednesday November 5, 2014

It’s easy to see how the field lines go from a point charge, but what about around an oddly shaped object (like most objects are)? Here’s how you draw them:


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Click here to go to next lesson on Faraday’s Cage.

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Faraday’s Cage

Wednesday November 5, 2014
British physicist Michael Faraday, famous for his many contributions to science including electrochemistry and electromagnetism.
British physicist Michael Faraday, famous for his many contributions to science including electrochemistry and electromagnetism.

Michael Faraday also discovered how you can have an electric field inside a charged conductor. Image you have a room within a room, and the inner room is made completely of metal. You can sit in the inner room with a static charge detector (like an electroscope), and when you charge the surfaces of both rooms, you’ll see sparks flying between the two rooms, but it’s peacefully (electrically speaking) quiet in the inner room. No charge is detected inside the inner room with your electroscope. You can have a bolt of lightning strike the inner room, but it still doesn’t register a charge inside the inner room. Why is that?


The inner room I’ve just described is called a “Faraday Cage”, and it’s often seen at science and magic shows because it absolutely defies common sense, until you really think about it. The inner room is shielding you from electric fields. Any closed conducting surface can be a Faraday cage. By closed, I mean electrically speaking. The cage can be a cage made of bars or chicken wire, but it’s still got to be electrically closed.  During the experiment, you can even run your hands on the inside of the room and still not get a shock from the sparks flying around between the rooms!


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The Faraday cage takes the electrostatic charges and redistributes them evenly around the exterior of the cage. As the cage distributes the charges, it cancels out the electric charges within the interior, making the cage a hollow conductor that has charge only on the external surface.


Click here to go to next lesson on Potential Energy.

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Potential Energy

Wednesday November 5, 2014

You’re already familiar with two different kinds of potential energy: elastic (like the energy stored in a rubber band) and gravitational (the energy stored in height). Now let’s take a look at electrical potential energy stored in an electric field:


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Click here to go to next lesson on Electric Potential.

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Electric Potential

Wednesday November 5, 2014

Ever wonder where the “volt” comes from? We’re going to look at this more in the next section on DC current, but here’s a snapshot overview of electric potential:


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Click here to go to next lesson on Static Electricity Fun.

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Static Electricity Fun

Wednesday November 5, 2014

If you have a Fun Fly Stick, then pull it out and watch the video below. If not, don’t worry – you can do most of these experiments with a charged balloon (one that you’ve rubbed on your hair). Let’ play with a more static electricity experiments, including making things move, roll, spin, chime, light up, wiggle and more using  static electricity!


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Materials:


  • sheet of paper
  • two empty, clean soup cans
  • aluminum foil
  • long straight pin
  • three film canisters (or M&M containers)
  • penny
  • sheet of paper
  • neon bulb
  • small styrofoam ball
  • fishing line or thread
  • chopstick
  • foam cup
  • dozen small aluminum pie tins
  • hot glue with glue sticks
  • Fun Fly Stick (also called “Wonder Fly Stick”)

This video show you how to get the most out of your Fun Fly Stick. If you don’t have a Fly Stick, simply use an inflated balloon that you’ve rubbed on your head. In the video, the Electrostatic Lab is mounted on a foam meat tray I found at the grocery store.



Download Student Worksheet & Exercises


The triboelectric series is a list that ranks different materials according to how they lose or gain electrons. Near the top of the list are materials that take on a positive charge, such as air, human skin, glass, rabbit fur, human hair, wool, silk, and aluminum. Near the bottom of the list are materials that take on a negative charge, such as amber, rubber balloons, copper, brass, gold, cellophane tape, Teflon, and silicone rubber.


When you turn on your Fun Fly Stick (or rub your head with a balloon), one end of the Fun Fly Stick takes on a positive charge and the other end holds the negative charge. When you rub your head with a balloon, the hair takes on a positive charge and the balloon takes on a negative charge.


When you scuff along the carpet, you build up a static charge (of electrons). Your socks insulate you from the ground, and the electrons can’t cross your sock-barrier and zip back into the ground. When you touch someone (or something grounded, like a metal faucet), the electrons jump from you and complete the circuit, sending the electrons from you to them (or it).


Exercises


  1. What is common throughout all these experiments that make them work?
  2. What makes the neon bulb light up? What else would work besides a neon bulb?
  3. Does it matter how far apart the soup cans are?
  4. Why does the foil ball go back and forth between the two cans?
  5.  Why do the pans take on the same charge as the Fly Stick?
  6.  When sticking a sheet of paper to the wall, does it matter how long you charge the paper for?
  7.  Draw a diagram to explain how the electrostatic motor works. Label each part and show where the charges are and how they make the rotor turn.

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Click here to go to next lesson on Alien Detector.

Alien Detector

Wednesday November 5, 2014

fet1This simple FET circuit is really an electronic version of the electroscope. This “Alien Detector” is a super-sensitive static charge detector made from a few electronics parts. I originally made a few of these and placed them in soap boxes and nailed the lids shut and asked kids how they worked. (I did place a on/off switch poking through the box along with the LED so they would have ‘some’ control over the experiment.)


This detector is so sensitive that you can go around your house and find pockets of static charge… even from your own footprints! This is an advanced project for advanced students.


You will need to get:


  • 9V battery clip (and a 9V battery)
  • MPF 102  (buy 2 – one for back up)
  • LED (any regular LED works fine)

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Download Student Worksheet & Exercises


After you’ve made your charge detector, turn it on and comb your hair, holding the charge detector near your head and then the comb. You’ll notice that the comb makes the LED turn off, and your head (in certain spots) makes the LED go on. So it’s a positive charge static detector… this is important, because now you know when the LED is off, the space you’re detecting is negatively charged, and when it’s lit up, you’re in a pocket of positively charged particles. How far from the comb does your detector need to be to detect the charge? Does it matter how humid it is?


You can take your detector outdoors, away from any standing objects like trees, buildings, and people, and hold it high in the air. What does the LED look like? What happens when you lower the detector closer to the ground? Raise it back up again to get a second reading… did you find that the earth is negative, and the sky is more positive?


You can increase the antenna sensitivity by dangling an extra wire (like an alligator clip lead) to the end of the antenna. Because thunderstorms are moving electrical charges around (negative charges downwards and positive charges upwards), the earth is electrified negatively everywhere. During a thunderstorm, the friction caused by the moving water molecules is what causes lightning to strike! (But don’t test your ideas outside in the wide open while lightening is striking!)


Exercises


  1. When the LED is on, what do you think it means?
  2. Does the LED turning off detect anything?
  3. Do aliens like humidity?
  4. How does this alien detector really work?

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Click here to go to next lesson on Lightning.

Lightning

Wednesday November 5, 2014

What causes lightning, and how can we protect ourselves from strikes? In many textbooks, you’ll read about how clouds become electrically charged through friction in the moist air, but the truth is, scientists still don’t fully understand how and why lightning happens the way it does. But here’s what we do know: lightning happens when the positive and negative charges in a cloud become polarized. That is, the (extra) positive charges move to the top of the cloud and the (extra) negative charges move to the bottom of the cloud, usually by friction of the water vapor molecules in the cloud.


As the water molecules rise, electrons are stripped off and add to the charge of the cloud. The cloud can become ever more polarized if the rising water vapor freezes. The frozen particles clump together and take on a negative charge inside, positive charge on the outside, which rips the clumps apart to further polarize the cloud. The more polarized the cloud is, the more its electric field affects the space around it. The electrons on the surface of the Earth underneath the cloud are repelled by the bottom of the cloud, which creates a positive charge on the surface under the cloud. Trees. houses, cars, and people take on a positive charge as the cloud passes by.  Now we’re set up for a lightning strike.


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Even though a bolt of lightning can have 10 coulombs of charge, a coin contains about 250,000 coulombs of positive charge (balanced by the same amount of negative charge). There is a whole lot of electric charge that is in ordinary matter, but since it’s balanced, it’s not as noticeable as the lightning strike!


Yay! You’ve completed this set of lessons! Now it’s your turn to do physics problems on your own.


Download your Static Electricity Problem Set here.

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Electric Force

Wednesday November 5, 2014

The way charges attract or repel each other can be described as a force. A charge can exert a push or pull on another charge depending on if the charges are positive or negative. How much force they exert can be figured out using Coulomb’s Law of Electric Force, which is:



where  C = 8.99 x 109 Nm2/C2


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Now Coulomb’s Law looks a lot like Newton’s Law of Gravitation… they both have a constant out in front, and they both have the inverse square relationship relating distance to force. They are different, however in a couple of important ways. Newton’s Law of Gravitation breaks down on the atomic level, and has to be replaced with Quantum Mechanics. Also, gravity is only an attractive force, whereas electric forces are both attractive and repulsive.



 


Notice the inverse square relationship: if you double the distance two charges are standing apart, the electrical force felt by the charges will decrease by a factor of four. If you triple the distance, the force goes down by a factor of nine.


Teachers and students both like to study, teach and learn subjects in neat, separate little packages, but this isn’t the way the universe works. Things aren’t usually isolated in their own box so they nothing to do with anything else. When we learned about the inverse square law, it wasn’t only for Newton’s Law of Gravitation… it popped up here also! And Newton’s Laws included forces, acceleration, gravity and energy, and now we’re going to add in an electrical force. But what does electrical force have to do with Newton’s Laws?


Click here to go to next lesson on Coulomb’s Law and Newton’s Laws.

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Coulomb’s Law and Newton’s Laws

Wednesday November 5, 2014

You can’t do an experiment on the planet without gravity playing some part of it (albeit sometimes so small you can ignore gravitational effects) since we’re in the Earth’s gravitational field. The electrical forces will add another force vector to our FBD that can be used when we look at how objects move in reaction to the forces.


Let’s take a look at how this works:


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Click here to go to next lesson on Charges in Objects.

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Charges in Objects

Wednesday November 5, 2014

How much charge do you think is inside a penny? What would happen if you could separate the positive and negative charges? How much force would each bundle of charge experience? Here’s how you find out:


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Click here to go to next lesson on Forces in an Atom.

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Forces in an Atom

Wednesday November 5, 2014

As a physics student, I wondered how much of a pulling force was between the nucleus of an atom and the electrons. Let’s look at the simplest atom (hydrogen) and find the attractive force between the proton and the electron:


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Click here to go to next lesson on Why do Protons Stick Together Inside the Nucleus?

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Why do Protons Stick Together Inside the Nucleus?

Wednesday November 5, 2014

Wasn’t that incredible how much force was present just between the two? After I figured that out, I wanted to know how much “push” was present between two protons in the nucleus. If you think about it, there’s really no reason for the protons to stick together inside the nucleus because they are all positively charged. Let’s take a look at the iron atom as we figure this out…


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There are four types of forces. They are, in order of strength: the strong nuclear force, electromagnetism, weak nuclear force, and gravity. That’s it. Those are all the forces that do all the pushing and pulling in the entire universe. The strong and weak nuclear forces are responsible for holding atoms together. They are quite important as you can imagine!


What kind of forces do protons inside the nucleus of an atom experience?  They are both positive charges, and really they don’t have any reason to stay together inside the nucleus as they’d be experiecing a repulsive force with each other. Let’s see exactly how big this repulsive force is:



 
Of all the forces, gravity is the weakling. It is actually much weaker than the other three. (In fact, in a way the other three have a tendency to pick on gravity, which isn’t very nice.)


Click here to go to next lesson on Electric Fields.

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Charging Methods

Wednesday November 5, 2014
[am4show have='p8;p9;p76;p20;p47;p97;p58;' guest_error='Guest error message' user_error='User error message' ] How are charges created? And how much? There's a scientific way to measure it.
  And what about lightning? How does that work when it comes to static charge?
    This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I've included it here so you can participate and learn, too! We're going to study electrons and static charge. Kids will build simple electrostatic motor to help them understand how like charges repel and opposites attract. After you've completed this teleclass, be sure to hop on over the teleclass in Robotics! Electrons are strange and unusual little fellows. Strange things happen when too many or too few of the little fellows get together. Some things may be attracted to other things or some things may push other things away. Occasionally you may see a spark of light and sound. The light and sound may be quite small or may be as large as a bolt of lightning. When electrons gather, strange things happen. Those strange things are static electricity. Materials:
  • Balloon (7-9", inflated with air, not helium)
  • AA battery case
  • 2 AA batteries for your battery case (cheap dollar-store “heavy duty” type are perfect. Don't use alkaline batteries if you can help it, because kids are going to short circuit their circuits, and the cheaper kind are safer in case they do.)
  • 1-2 LEDs
  • Alligator wires
  • 1.5-3V DC motor
  • 3-6V buzzer
If you want to make the laser burglar alarm, then get these also:
  • OPTIONAL: CdS Photoresistor for the laser burglar alarm
  • OPTIONAL: 9V Battery for laser burglar alarm
  • OPTIONAL: Laser pointer (the cheap kind from the dollar store work great) or strong flashlight for the laser burglar alarm
If you want to make the first robotics projects then also get these:
  • OPTIONAL: block of foam (any kind will do that is at least 2" on each side)
  • OPTIONAL: 10 (or more) wood skewers at least 4" long
  • OPTIONAL: 1 wood clothespin
  • OPTIONAL: Hot glue and glue sticks (with adult help)
If you want to make the second robotics project then also get these:
  • OPTIONAL: Additional 3V DV motor (you need two for this project)
  • OPTIONAL: 6 large popsicle sticks (tongue depressor size)
  • OPTIONAL: Tack or other sharp object for poking holes
  • OPTIONAL: Hot glue and glue sticks (with adult help)
 
 

Key Concepts

The proton has a positive charge, the neutron has no charge (neutron, neutral get it?) and the electron has a negative charge. These charges repel and attract one another kind of like magnets repel or attract. Like charges repel (push away) one another and unlike charges attract one another. Generally things are neutrally charged. They aren't very positive or negative, rather have a balance of both. Things get charged when electrons move. Electrons are negatively charged particles. So if an object has more electrons than it usually does, that object would have a negative charge. If an object has less electrons than protons (positive charges), it would have a positive charge. How do electrons move? It turns out that electrons can be kind of loosey goosey. Depending on the type of atom they are a part of, they are quite willing to jump ship and go somewhere else. The way to get them to jump ship is to rub things together. Like in our experiment we're about to do...

What's Going On?

In static electricity, electrons are negatively charged and they can move from one object to another. This movement of electrons can create a positive charge (if something has too few electrons) or a negative charge (if something has too many electrons). It turns out that electrons will also move around inside an object without necessarily leaving the object. When this happens the object is said to have a temporary charge. When you rub a balloon on your head, the balloon is now filled up with extra electrons, and now has a negative charge. Opposite charges attract right? So, is the entire yardstick now an opposite charge from the balloon? No. In fact, the yardstick is not charged at all. It is neutral. So why did the balloon attract it? The balloon is negatively charged. It created a temporary positive charge when it got close to the yardstick. As the balloon gets closer to the yardstick, it repels the electrons in the yardstick. The negatively charged electrons in the yardstick are repelled from the negatively charged electrons in the balloon. Since the electrons are repelled, what is left behind? Positive charges. The section of yardstick that has had its electrons repelled is now left positively charged. The negatively charged balloon will now be attracted to the positively charged yardstick. The yardstick is temporarily charged because once you move the balloon away, the electrons will go back to where they were and there will no longer be a charge on that part of the yardstick. This is why plastic wrap, Styrofoam packing popcorn, and socks right out of the dryer stick to things. All those things have charges and can create temporary charges on things they get close to.

Questions to Ask

  1. Does the shape of the balloon matter? Does hair color matter?
  2. What happens if you rub the balloon on other things, like a wool sweater?
  3. If you position other people with charged balloons around the table, can you keep the yardstick going?
  4. Can we see electrons?
  5. How do you get rid of extra electrons?
  6. Rub a balloon on your head, and then lift it up about 5 inches. Why is the hair attracted to the balloon?
  7. Why does the hair continue to stand on end after the balloon is taken away?
  8. Why do you think the yardstick moved?
  9. What other things are attracted or repelled the same way by the balloon? (Hint: try a ping pong ball.)
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Click here to go to next lesson on Triboelectric series.

 

Triboelectric Series

Wednesday November 5, 2014

The Triboelectric Effect is a type of electrification that happens when you rub two different materials together and then separate them. Often, one will take on a positive charge and the other a negative. But how do you know which is going to be which?


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A bolt of lightning carries a LOT of extra excess electrons. We can calculate how much using a simple calculation.



No matter how hard you try, if you hae a copper rod that you rub with a cloth, you just can’t get a charge to build up on it. Why is that?



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Click here to go to next lesson on Electrostatic Motors.

Electrostatic Motor

Wednesday November 5, 2014

You can use the idea that like charges repel (like two electrons) and opposites attract to move stuff around, stick to walls, float, spin, and roll. Make sure you do this experiment first.


I’ve got two different videos that use positive and negative charges to make things rotate, the first of which is more of a demonstration (unless you happen to have a 50,000 Volt electrostatic generator on hand), and the second is a homemade version on a smaller scale.


Did you know that you can make a motor turn using static electricity? Here’s how:


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Download Student Worksheet & Exercises


Here’s how the electrostatic machine works – you will need:


  • a yardstick
  • spoon
  • balloon


How does it work? Different parts of the atom have different electrical charges. The proton has a positive charge, the neutron has no charge (neutron, neutral get it?) and the electron has a negative charge. These charges repel and attract one another kind of like magnets repel or attract. Like charges repel (push away) one another and unlike charges attract one another.


So if two items that are both negatively charged get close to one another, the two items will try to get away from one another. If two items are both positively charged, they will try to get away from one another. If one item is positive and the other negative, they will try to come together.


How do things get charged? Generally things are neutrally charged. They aren’t very positive or negative. However, occasionally (or on purpose as we’ll see later) things can gain a charge. Things get charged when electrons move. Electrons are negatively charged particles. So if an object has more electrons than it usually does, that object would have a negative charge. If an object has less electrons than protons (positive charges), it would have a positive charge.


How do electrons move? It turns out that electrons can be kind of loosey-goosey. Depending on the type of atom they are a part of, they are quite willing to jump ship and go somewhere else. The way to get them to jump ship is to rub things together.


Remember, in static electricity, electrons are negatively charged and they can move from one object to another. This movement of electrons can create a positive charge (if something has too few electrons) or a negative charge (if something has too many electrons). It turns out that electrons will also move around inside an object without necessarily leaving the object. When this happens the object is said to have a temporary charge.


Try this: Blow up a balloon. When you rub the balloon on your head, the balloon is now filled up with extra electrons, and now has a negative charge. Now stick it to a wall— to create a temporary charge on a wall.


Opposite charges attract right? So, is the entire wall now an opposite charge from the balloon? No. In fact, the wall is not charged at all. It is neutral. So why did the balloon stick to it?


The balloon is negatively charged. It created a temporary positive charge when it got close to the wall. As the balloon gets closer to the wall, it repels the electrons in the wall. The negatively charged electrons in the wall are repelled from the negatively charged electrons in the balloon.


Since the electrons are repelled, what is left behind? Positive charges. The section of wall that has had its electrons repelled is now left positively charged. The negatively charged balloon will now “stick” to the positively charged wall. The wall is temporarily charged because once you move the balloon away, the electrons will go back to where they were and there will no longer be a charge on that part of the wall.


This is why plastic wrap, Styrofoam packing popcorn, and socks right out of the dryer stick to things. All those things have charges and can create temporary charges on things they get close to.


Want to purchase an electrostatic machine? Here’s a link to the one used in the video called a Wimshurst Machine which makes sparks up to 4″ long. For younger kids, we recommend this fun hand-held, non-shocking electrostatic generator.


Exercises


  1.  What happens if you rub the balloon on other things, like a wool sweater?
  2.  If you position other people with charged balloons around the table, how long can you keep  the yardstick going
  3.  Can we see electrons?
  4.  How do you get rid of extra electrons?
  5.  Why do you think the yardstick moved?
  6.  What would happen if you use both a positively charged object and a negatively charged  object to make the yardstick move?

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Click here to go to next lesson on Coulomb’s Law.

Coulomb’s Law

Wednesday November 5, 2014

Induction is another way to create a charge in an object. You can charge an object by induction without even touching it. I’ve got a couple of really neat experiments that will show you how this works, but here’s the basic idea: when you have two metal objects, like two soda cans, standing upright on a foam slab and just touching each other (so they are insulated from the table but in contact with each other), you can bring a charged balloon close to one of them and see a really interesting effect: the can closest to the charged balloon (which has a negative charge) will take on a positive charge, and the soda can furthest from the balloon will take on a negative charge. And when you separate the two cans, the charges on each will be evenly distributed over the surface of each can and remain polarized (the further can keeps its negative charge and the closer can keeps its positive charge). That’s charging by induction!


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Note that the net charge of the system was zero when you started, and is still zero when you finish, even though the electrons have moved and the charge on each can is different than when you started. Charge cannot be created or destroyed, however it can be transferred from one object to another by electrons. If you touch the soda can while you’re charging it, the electrons will enter your hand and “go to ground” and discharge your system. Humidity also does this using water vapor – the water molecules will dissipate your static charge build up so it looks like your static electricity experiments don’t work! However, if you bring a positively charged object near the soda cans and then touch the can, electrons will be attracted and actually create a larger static charge on the can.


This idea of “grounding” simply means that the excess charge (either positive or negative) can be removed by transferring electrons from something really big, like the Earth, that acts like a huge ocean of electrons.


Click here to go to next lesson on Electroscope.

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Electroscope

Wednesday November 5, 2014

When high energy radiation strikes the Earth from space, it’s called cosmic rays. To be accurate, a cosmic ray is not like a ray of sunshine, but rather is a super-fast particle slinging through space. Think of throwing a grain of sand at a 100 mph… and that’s what we call a ‘cosmic ray’. Build your own electroscope with this video!


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Materials:


  • Clean glass jar with a lid
  • Wire coat hanger and sand paper
  • Aluminum foil
  • Vice grips or a hacksaw
  • Scissors
  • Balloon or other object to create a static charge
  • Hot glue gun (optional)


Download Student Worksheet & Exercises


Troubleshooting: This device is also known as an electroscope, and its job is to detect static charges, whether positive or negative.  The easiest way to make sure your electroscope is working is to rub your head with a balloon and bring it near the foil ball on top – the foil “leaves” inside the jar should spread apart into a V-shape.


Exercises


  1. How does this detector work?
  2. Do all particles leave the same trail?
  3. What happens when the magnet is brought close to the jar?

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Electrophorus

Wednesday November 5, 2014

Jupiter not only has the biggest lightning bolts we’ve ever detected, it also shocks its moons with a charge of 3 million amps every time they pass through certain hotspots. Some of these bolts are cause by the friction of fast-moving clouds. Today you get to make your own sparks and simulate Jupiter’s turbulent storms.


Electrons are too small for us to see with our eyes, but there are other ways to detect something’s going on. The proton has a positive charge, and the electron has a negative charge. Like charges repel and opposite charges attract.


Materials


  • Foam plate
  • Foam cup
  • Wool cloth or sweater
  • Plastic baggie
  • Aluminum pie pan
  • Aluminum foil
  • Film canister or M&M container
  • Nail (needs to be a little longer than the film canister)
  • Hot glue gun or tape
  • Water

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Download Student Worksheet & Exercises


  1. Lay the aluminum pie pan in front of you, right-side up.
  2. Glue the foam cup to the middle of the inside of the pan.
  3. Lay the plate on the table, upside down. Place the pie pan (don’t glue it!) on top of the plate, back-to-back. Set aside.
  4. Insert the nail through the middle of the film canister lid. Wrap the bottom of the film canister with aluminum foil. Tape the foil into place.
  5. Fill the canister nearly full of water.
  6. Snap on the lid, making sure that the nail touches the water.
  7. Rub the foam plate with the wool for at least a minute to really charge it up. Place the plate upside down carefully on the table.
  8. Put the pie pan back on top of the foam plate. The plate has taken on the charge from the foam plate.
  9. Touch the pie pan with a finger… did you feel anything?
  10. Use the cup as a handle and lift the pie pan up.
  11. Touch the pan with your finger, and you should feel and see a spark (turn down the lights to make the room dark).
  12. Charge the foam plate again and set the pie pan back on top to charge it up. (Make sure you’re lifting the pie pan only by the foam cup, or you’ll discharge it accidentally.)
  13. Hold the film canister by the aluminum foil and touch the charged pie pan to the nail.
  14. Rub the foam plate with the wool again to charge it up. Set the pie pan on the foam plate to charge the pan. Now lift the pie pan and touch the pan to the nail. Do this a couple of times to really get a good charge in the film canister.
  15. Discharge the film canister by touching the foil with one finger and the nail with the other. Did you see a spark?
  16. The wool gives the plate a negative charge. You can use a plastic bag instead of the wool to give the foam plate a positive charge.

What’s Going On?

If you rub a balloon on your head, the balloon becomes filled up with extra electrons, and now has a negative charge. Try the following experiment to create a temporary charge on a wall: Bring the balloon close to the wall until it sticks.


Opposite charges attract right? So, is the entire wall now an opposite charge from the balloon? No. In fact, the wall is not charged at all. It is neutral. So why did the balloon stick to it?


The balloon is negatively charged. It created a temporary positive charge when it got close to the wall. As the balloon gets closer to the wall, it repels the electrons in the wall. The negatively charged electrons in the wall are repelled from the negatively charged electrons in the balloon.


Since the electrons are repelled, what is left behind? Positive charges. The section of wall that has had its electrons repelled is now left positively charged. The negatively charged balloon will now “stick” to the positively charged wall. The wall is temporarily charged because once you move the balloon away, the electrons will go back to where they were and there will no longer be a charge on that part of the wall.


This is why plastic wrap, Styrofoam packing popcorn, and socks right out of the dryer stick to things. All those things have charges and can create temporary charges on things they get close to.


If you rub a balloon all over your hair, the Triboelectric Effect causes the electrons to move from your head to the balloon. But why don’t the electrons go from the balloon to your head? The direction of electron transfer has to do with the properties of the material itself. And the balloon-hair combination isn’t the only game in town.


Electrons move differently depending on the materials that are rubbed together. A balloon takes on a negative charge when rubbed on hair. Today, the kids are going to find when a foam plate is rubbed with wool, the plate takes on electrons and creates a negative charge on the plate. To give the plate a positive charge, kids can rub it with a plastic bag.


The Triboelectric Series is a list that ranks different materials according to how they lose or gain electrons. A rubber rod rubbed with wool produces a negative charge on the rod, however an acrylic rod rubbed with silk creates a positive charge on the rod. A foam plate often has a positive charge when you slide one off the stack, but if you rub it with wool it will build up a negative charge.


Near the top of the list are materials that take on a positive charge, such as air, human skin, glass, rabbit fur, human hair, wool, silk, and aluminum. Near the bottom of the list are materials that take on a negative charge, such as amber, rubber balloons, copper, brass, gold, cellophane tape, Teflon, and silicone rubber. Scientists developed this list by doing a series of experiments, very similar to the ones we’re about to do.


Exercises


  1. What happens if you hold the nail and charge the aluminum foil?
  2. Can you see electrons? Why or why not?

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Click here to go to next lesson on Easy Photoelectric Effect Experiment

Easy Photoelectric Effect Experiment

Wednesday November 5, 2014

Photoelectric EffectEinstein received a Nobel Prize for figuring out what happens when you shine blue light on a sheet of metal.  When he aimed a blue light on a metal plate, electrons shot off the surface. (Metals have electrons which are free to move around, which is why metals are electrically conductive. More on this in Unit 10).


When Einstein aimed a red light at the metal sheet, nothing happened.  Even when he cranked the intensity (brightness) of the red light, still nothing happened.  So it was the energy of the light (wavelength), not the number of photons (intensity) that made the electrons eject from the plate. This is called the ‘photoelectric effect’. Can you imagine what happens if we aim a UV light (which has even more energy than blue light) at the plate?


This photoelectric effect is used by all sorts of things today, including solar cells, electronic components, older types of television screens, video camera detectors, and night-vision goggles.


This photoelectric effect also causes the outer shell of orbiting spacecraft to develop an electric charge, which can wreck havoc on its internal computer systems.


A surprising find was back in the 1960s, when scientists discovered that moon dust levitated through the photoelectric effect. Sunlight hit the lunar dust, which became (slightly) electrically charged, and the dust would then lift up off the surface in thin, thread-like fountains of particles up ¾ of a mile high.


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Materials:


  • soda or steel can
  • paper clip
  • sand paper
  • tinsel (or aluminum foil and scissors)
  • tape
  • foam cup
  • PVC pipe (any size)
  • brown paper bag
  • UV shortwave lamp (sometimes called a “germ-free portable lamp”)


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Click here to go to next lesson on Charging by Induction and Conduction.

Charging by Induction and Conduction

Wednesday November 5, 2014

Ygou can also charge objects by conduction. You’ve actually already done with without really thinking about it. The foil on the wire coat hanger in the electroscope was being charged by conduction. When you touch a charged balloon to the foil ball on the electroscope, that’s a charge by conduction. If you were to get the charged balloon really close but not touching the foil ball, that would be charging by induction. (See the difference?) Charging by conduction just means that you need to touch the electrically neutral object to the one that is charged to transfer the charge. It’s charge by contact.


With charge by induction, it’s the forces due to likes repelling and opposites attracting that cause the charge in objects. With conduction, it’s the actual movement of electrons to the object that make the charge in the object. This is obvious if you think about touching two soda cans together, since they are both made out of a material that allows electrons to move about freely within the material (on the surface of the object). But what about two insulators, like two foam plates? What happens then?


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Insulators do not conduct charge the way that conductors do. Even if two foam plates are touching, charge can not be conducted from one foam plate to another, or even from a foam plate to a soda can. However the foam plate can polarize the soda can through electrical forces (opposite charges attracting and lie charges repelling).


Click here to go to next lesson on Electric Force.

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Basic Fundamentals

Wednesday November 5, 2014

This experiment is just for advanced students. If you guessed that this has to do with electricity and chemistry, you’re right! But you might wonder how they work together. Back in 1800, William Nicholson and Johann Ritter were the first ones to split water into hydrogen and oxygen using electrolysis. (Soon afterward, Ritter went on to figure out electroplating.) They added energy in the form of an electric current into a cup of water and captured the bubbles forming into two separate cups, one for hydrogen and other for oxygen.


This experiment is not an easy one, so feel free to skip it if you need to. You don’t need to do this to get the concepts of this lesson but it’s such a neat and classical experiment (my students love it) so you can give it a try if you want to. The reason I like this is because what you are really doing in this experiment is ripping molecules apart and then later crashing them back together.


Have fun and please follow the directions carefully. This could be dangerous if you’re not careful. The image shown here is using graphite from two pencils sharpened on both ends, but the instructions below use wire.  Feel free to try both to see which types of electrodes provide the best results.


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You will need:


  • 2 test tubes or thin glass or plastic something closed at one end. I do not recommend anything wider than a half inch in diameter.
  • 2 two wires, one needs to be copper, at least 12 inches long. Both wires need to have bare ends.
  • 1 Cup
  • Water
  • One 9 volt battery
  • Long match or a long thin piece of wood (like a popsicle stick) and a match
  • Rubber bands
  • Masking tape
  • Salt


Download Student Worksheet & Exercises
1. Fill the cup with water.


2. Put a tablespoon or so of salt into the water and stir it up. (The salt allows the electricity to flow better through the water.)


2. Put one wire into the test tube and rubber band it to the test tube so that it won’t come out (see picture).


3. Use the masking tape to attach both wires to the battery. Make sure the wire that is in the test tube is connected to the negative (-) pole of the battery and that the other is connected to the positive (+) pole. Don’t let the bare parts of the different wires touch. They could get very hot if they do.


4. Fill the test tube to the brim with the salt water.


5. This is the tricky part. Put your finger over the test tube, turn it over and put the test tube, open side down, into the cup of water. (See picture.)


6. Now put the other wire into the water. Be careful not to let the bare parts of the wires touch.


7. You should see bubbles rising into the test tube. If you don’t see bubbles, check the other wire. If bubbles are coming from the other wire either switch the wires on the battery connections or put the wire that is bubbling into the test tube and remove the other. If you see no bubbles check the connections on the battery.


8. When the test tube is half full of gas (half empty of salt water depending on how you look at it) light the long match or the wooden stick. Then take the test tube out of the water and let the water drain out. Holding the test tube with the open end down, wait for five seconds and put the burning stick deep into the test tube (the flame will probably go out but that’s okay). You should hear an instant pop and see a flash of light. If you don’t, light the stick again and try it another time. For some reason, it rarely works the first time but usually does the second or third.


A water molecule, as you saw before, is two hydrogen atoms and one oxygen atom. The electricity encouraged the oxygen to react with the copper wire leaving the hydrogen atoms with no oxygen atom to hang onto. The bubbles you saw were caused by the newly released hydrogen atoms floating through the test tube in the form of hydrogen gas. Eventually that test tube was part way filled with nothing but pure hydrogen gas.


But how do you know which bubbles are which? You can tell the difference between the two by the way they ignite (don’t’ worry – you’re only making a tiny bit of each one, so this experiment is completely safe to do with a grown up).


It takes energy to split a water molecule. (On the flip side, when you combine oxygen and hydrogen together, it makes water and a puff of energy. That’s what a fuel cell does.) Back to splitting the water molecule – as the electricity zips through your wires, the water molecule breaks apart into smaller pieces: hydrogen ions (positively charged hydrogen) and oxygen ions (negatively charged oxygen). Remember that a battery has a plus and a minus charge to it, and that positive and negative attract each other.


So, the positive hydrogen ions zip over to the negative terminal and form tiny bubbles right on the wire. Same thing happens on the positive battery wire. After a bit of time, the ions form a larger gas bubble. If you stick a cup over each wire, you can capture the bubbles and when you’re ready, ignite each to verify which is which.


If the match burns brighter, the gas is oxygen. If you hear a POP!, the gas is hydrogen. Oxygen itself is not flammable, so you need a fuel in addition to the oxygen for a flame. In one case, the fuel is hydrogen, and hence you hear a pop as it ignites. In the other case, the fuel is the match itself, and the flame glows brighter with the addition of more oxygen.


When you put the match to it, the energy of the heat causes the hydrogen to react with the oxygen in the air and “POP”, hydrogen and oxygen combine to form what? That’s right, more water. You have destroyed and created water! (It’s a very small amount of water so you probably won’t see much change in the test tube.)


The chemical equations going on during this electrolysis process look like this:


A reduction reaction is happening at the negatively charged cathode. Electrons from the cathode are sticking to the hydrogen cations to form hydrogen gas:


2 H+(aq) + 2e– –> H2(g)


2 H2O(l) + 2e– –> H2(g) + 2 OH–(aq)


The oxidation reaction is occurring at the positively charged anode as oxygen is being generated:


2 H2O(l)  –> O2(g) + 4 H+(aq) + 4e–


4 OH–(aq) –> O2(g) + 2 H2O(l) + 4 e-


Overall reaction:


2 H2O(l)  –> 2 H2(g) + O2(g)


Note that this reaction creates twice the amount of hydrogen than oxygen molecules. If the temperature and pressure for both are the same, you can expect to get twice the volume of hydrogen to oxygen gas (This relationship between pressure, temperature, and volume is the Ideal Gas Law principle.)


This is the idea behind vehicles that run on sunlight and water.  They use a solar panel (instead of a 9V battery) to break apart the hydrogen and oxygen and store them in separate tanks, then run them both back together through a fuel cell, which captures the energy (released when the hydrogen and oxygen recombine into water) and turns the car’s motor. Cool, isn’t it?


Note: We’re going to focus on Alternative Energy in Unit 12 and create all sorts of various energy sources including how to make your own solar battery, heat engine, solar & fuel cell vehicles (as described above), and more!


Exercises


  1. Why are bubbles forming?
  2. Did bubbles form at both wires, or only one? What kind of bubbles are they?
  3. What would happen if you did this experiment with plain water? Would it work? Why or why not?
  4. Which terminal (positive or negative) produced the hydrogen gas?
  5. Did the reaction create more hydrogen or more oxygen?

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Click here to go to next lesson on Molecules and Atoms.

Molecules and Atoms

Wednesday November 5, 2014
Oxygen Atomic Diagram

Let’s try another way to look at this. You’re playing miniature golf and you come to the old wind mill hole. Your friend takes a shot and since the blades of the windmill are going nice and slow he gets the ball right through. Now it’s your turn. Suddenly you hear a zap and a pow and sparks go flying. Something has gone wrong with the wind mill and it starts spinning at amazing speeds. You decide to give it a try and hit the ball towards the wind mill.


Well since it is spinning out of control, those blades now form almost a solid disk so that there is no way your ball can get through the wind mill. Electrons do the same thing. They move so fast that even though there may not be many of them, they form a shell that can’t be penetrated. (To be clear, particles that are smaller than an atom can go through the shells and pop out the other side.)



Let’s go a little further with this shell thing. An atom can have as few as one and as many as seven shells. Imagine our balloon again. Now there can be a balloon inside of a balloon inside a balloon and so on. Up to seven balloons! Each balloon, whoops, I mean shell, can have only so many electrons in it. This simple equation 2n2 tells you how many electrons can be in each shell. The n stands for the number of the shell.


The first shell can have up to 2 x 1(first shell)2 or 2 electrons. The second shell can have up to 2 x 2(second shell)2 or 8 electrons. The third shell can have up to 2 x 32 or 18 electrons. The fourth shell can have up to 2 x 42 or 32 electrons. All the way up to the seventh shell which can have 2 x 72 or 98 electrons!


One last thing about shells, the shells have to be full before the electrons will go to the next shell. A helium atom will have two electrons. Both of them will be in the first shell. A Lithium atom will have three electrons. Two will be in the first shell and one (since the first shell is filled) will be in the second shell.


Electrons provide the size and stability of the atom and, as such, the mass and the structure of all matter. Electrons are also the key to all electromagnetic energy. But wait, that’s not all! It is the number of electrons in an atom that determines if and how atoms come together to form molecules. Electrons determine how and what matter will be.


Atoms like to feel satisfied and they feel satisfied if they are “full”.  An atom is “full” if its outer electron shell has as many electrons as it can hold or if there are eight or a multiple of eight (16, 24 etc.) electrons in the outer shell. This is called the octet rule and works most of the time, but is not perfect.


If an atom is not full, it is not satisfied. An unsatisfied atom needs to do something with its electrons to be happy. Luckily atoms are very friendly and love to share. Most atoms are not satisfied as individuals. The oxygen atom has six electrons in its outer shell. It needs eight electrons to be satisfied.


Luckily, two Hydrogen atoms happen by. Each one of them has only one electron in its outer shell and needs one more to be satisfied. If both Hydrogens share their one electron with the Oxygen, the oxygen has eight electrons and is satisfied. Also, if the Oxygen shares an electron with each Hydrogen, then both Hydrogens are satisfied as well. Just like your mother told you, it’s nice to share. It is this sharing of electrons that makes atoms come together to form molecules.


Click here to go to next lesson on Electrostatic Charge.

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Electrostatic Charge

Wednesday November 5, 2014

To summarize, protons and neutrons are in the nucleus of an atom, and tightly bound together. The proton has a positive charge while the neutron has no charge, and both of them are much larger than the electron. The tiny electron is outside the nucleus and weakly bound to the atom and carries a negative a charge.


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Go get a balloon. The rubber latex kind work the best (not the shiny Mylar kind). You’ll need it for the next set of experiments we’re going to talk about below. When you rub a balloon on your head, you charge up the balloon with a negative static charge. But how much charge is it? The units of charge are called the Coulomb (C), just like the units of time are seconds (s). And just like seconds, you can have microseconds (10-6 seconds) and nanoseconds (10-9 seconds), you can have microCoulombs (10-6 C or μC) and nanoCoulombs (10-9 C or nC).


The charge of one electron is -1.6 x 10-19 C… it’s a really small number! The charge of one proton is +1.6 x 10-19 C. The kind of charge (whether positive or negative) is determined by how many extra protons or electrons are present in addition to the ones that are evenly matched to balance the charge. If an object has 15 protons and 17 electrons, then it’s got a negative charge by 2 electrons. Just because an object is not charged (electrically neutral) doesn’t mean it doesn’t have any protons or electrons. Rather it means that the number of electrons and protons are evenly matched to balance the charge of the object. We say that charge is quantized, which means that electric charge isn’t a continuous fluid flow, but instead is made up of tiny packets of charged particles. The charge on one electron is -1.60 x 10-19 C.  This is one of the most fundamental concepts in physics! 


Click here to go to next lesson on The Charge of Lightning.

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The Charge of Lightning

Wednesday November 5, 2014

Let’s go back to rubbing a balloon on your head. When you do this and bring it close to objects like a thin stream of water trickling out of the faucet, or small its of paper, or bubbles in the air, or even a ping pong ball on the table, did you notice now you can influence things? You can make water flick and spray, paper jump up and down, and bubbles and ping pong balls will follow your every move. But why is that?


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Click here to go to next lesson on Maxwell’s First Equation.

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Maxwell’s First Equation

Wednesday November 5, 2014

The influence you’re exerting on these objects is called the electric force,  which is a non-contact force that can happen over a distance.


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James Maxwell, a Scottish theoretical physicist who made important contributions to electromagnetic theory.
James Maxwell, a Scottish theoretical physicist who made important contributions to electromagnetic theory.

Did you notice that you can exert a force on an object without touching it? Try it now if you haven’t already! Did you notice how opposite charges attract and like charges repel? That’s the fundamental key concept with this section.  Electrical force are the attractive for opposite charges and repulsive for like charges. Electrical force is also attractive between a charged and a neutral object.


Click here to go to next lesson on Conductors and Insulators.

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Simple Electrical Conductivity Circuit

Wednesday November 5, 2014

An electrical circuit is like a NASCAR raceway.  The electrons (racecars) zip around the race loop (wire circuit) superfast to make stuff happen. Although you can’t see the electrons zipping around the circuit, you can see the effects: lighting up LEDs, sounding buzzers, clicking relays, etc.


There are many different electrical components that make the electrons react in different ways, such as resistors (limit current), capacitors (collect a charge), transistors (gate for electrons), relays (electricity itself activates a switch), diodes (one-way street for electrons), solenoids (electrical magnet), switches (stoplight for electrons), and more.  We’re going to use a combination diode-light-bulb (LED), buzzers, and motors in our circuits right now.


A CIRCUIT looks like a CIRCLE.  When you connect the batteries to the LED with wire and make a circle, the LED lights up.  If you break open the circle, electricity (current) doesn’t flow and the LED turns dark.


LED stands for “Light Emitting Diode”.  Diodes are one-way streets for electricity – they allow electrons to flow one way but not the other.


Remember when you scuffed along the carpet?  You gathered up an electric charge in your body.  That charge was static until you zapped someone else.  The movement of electric charge is called electric current, and is measured in amperes (A). When electric current passes through a material, it does it by electrical conduction. There are different kinds of conduction, such as metallic conduction, where electrons flow through a conductor (like metal) and electrolysis, where charged atoms (called ions) flow through liquids.


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Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 2 alligator wires
  • LEDs (any you choose is fine)


Download Student Worksheet & Exercises


Be alert for:


1. Batteries inserted into the case the wrong way!


2. LED in the wrong way (LEDs are picky about plus and minus – they are POLARIZED)


3. Is there a metal-to-metal connection?  (You’re not grabbing ahold of the plastic insulation, are you?)


4. Bad wires can cause headaches – if all else fails, then swap out your alligator clip lead wires for new ones.


Exercises


  1. What does LED stand for?
  2. Does it matter which way you wire an LED in a circuit?
  3. Does the longer wire on the LED connect to plus (red) or minus (black)?
  4. Do you need to hook up batteries to make a neon bulb light up?  Why or why not?
  5. What’s the difference between a light bulb and your LED?
  6. What is the difference between a bolt of lightning and the electricity in your circuit?
  7. What is the charge of an electron?

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Click here to go to next lesson on Why does metal conduct electricity?

Why does metal conduct electricity?

Wednesday November 5, 2014

switch-zoomMake yourself a grab bag of fun things to test: copper pieces (nails or pipe pieces), zinc washers, pipe cleaners, Mylar, aluminum foil, pennies, nickels, keys, film canisters, paper clips, load stones (magnetic rock), other rocks, and just about anything else in the back of your desk drawer.


Certain materials conduct electricity better than others. Silver, for example, is one of the best electrical conductors on the planet, followed closely by copper and gold. Most scientists use gold contacts because, unlike silver and copper, gold does not tarnish (oxidize) as easily. Gold is a soft metal and wears away much more easily than others, but since most circuits are built for the short term (less than 50 years of use), the loss of material is unnoticeable.
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Modify your basic LED circuit into a Conductivity Circuit by removing one clip lead from the battery and inserting a third clip lead to the battery terminal. The two free ends are your new clips to put things in from the grab bag. Try zippers, metal buttons, barrettes, water from a fountain, the fountain itself, bike racks, locks, doorknobs, unpainted benches… you get the idea!


Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 3 alligator wires
  • LEDs (any you choose is fine)
  • paper clip
  • penny
  • other metal objects around your house (zippers, chairs, etc…)


Why does metal conduct electricity?

Why does metal, not plastic, conduct electricity? Imagine you have a garden hose with water flowing through it. The hose is like the metal wire, and the water is like the electric current. Trying to run electricity through plastic is like filling your hose with cement. It’s just the nature of the material.



Download Student Worksheet & Exercises


Exercises


  1.       Name six materials that are electrically conductive.
  2.        What kinds of materials are conductors and insulators?
  3.      Can you convert an insulator into a conductor? How?
  4.        Name four instances when insulators are a bad idea to have around.
  5.      When are insulators essential to have?

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Click here to go to next lesson on Liquid Conductors.

Liquid Conductors

Wednesday November 5, 2014

When an atom (like hydrogen) or molecule (like water) loses an electron (negative charge), it becomes an ion and takes on a positive charge. When an atom (or molecule) gains an electron, it becomes a negative ion. An electrolyte is any substance (like salt) that becomes a conductor of electricity when dissolved in a solvent (like water).


This type of conductor is called an ‘ionic conductor’ because once the salt is in the water, it helps along the flow of electrons from one clip lead terminal to the other so that there is a continuous flow of electricity.


This experiment is an extension of the Conductivity Tester experiment, only in this case we’re using water as a holder for different substances, like sugar and salt. You can use orange juice, lemon juice, vinegar, baking powder, baking soda, spices, cornstarch, flour, oil, soap, shampoo, and anything else you have around. Don’t forget to test out plain water for your ‘control’ in the experiment!


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Here’s what you need:


  • 2 AA batteries
  • AA battery case
  • 2 alligator clips
  • LED
  • water
  • salt
  • glass jar (like a clean jam jar)


Download Student Worksheet & Exercises


Exercises


  1. Why does electricity flow through some solutions but not all of them?
  2. What is a salt?
  3. How are electrolytes used today in real life?
  4. Which substance was your top conductor?
  5. Which substance didn’t conduct anything at all?
  6. What happens if you mix an electrolyte and non-electrolyte together?

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Click here to go to next lesson on Superconductors.

Superconductors

Wednesday November 5, 2014

When I was in 10th grade, my teammate and I designed what we thought was pretty clever: a superconductor roller coaster, which we imagined would float effortlessly above its magnetic track. Of course, our roller coaster was only designed on paper, because yttrium barium copper oxide ceramics had only just been discovered by top scientists.



Did you notice how it was smoking in the video? That’s because it was so cold! The usual problem with superconductors is that they need to be incredibly cold in order to exhibit superconductive properties.  Yttrium barium copper oxide (YBa2Cu3O7) was the first compound that used liquid nitrogen for cooling, making superconductors a lot less expensive to work with – you no longer needed a cryogenic lab in order to levitate objects above a magnet.



Recently, scientists have found a way to make an amazing superconductor by taking a single crystal sapphire wafer and coating it with a thin (~1µm thick) ceramic material (yttrium barium copper oxide). Normally, the ceramic layer has no interesting magnetic or electrical properties, but that’s when you’re looking at it at room temperature. If you cool this material below -185ºC (-301ºF), it turns out that the ceramic material becomes a superconductor, meaning that it conducts electricity without resistance, with no energy loss. Zero. That’s what makes it a ‘superconductor’.


To further understand superconductivity, it’s helpful to understand what normally happens to electricity as it flows through a wire. As you may know, energy cannot be created or destroyed, but can be changed from one form to another.


In the case of wires, some of the electrical energy is changed to heat energy. If you’ve ever touched a wire that had been in use for a while, and discovered it was hot, you’ve experienced this. The heat energy is a waste. It simply means that less electricity gets to its final destination.


This is why superconductivity is so cool (no pun intended.) By cooling things down to temperatures near absolute zero, which is as low as temperatures can get, you can create a phenomenon where electricity flows without having any of it converted to heat.


Why do superconductors float above magnets?

Scientists also figured out that superconductors and magnetic field really do not like each other. The Meissner effect happens when a superconductor expels all its magnetic fields from inside.


However, if you make your superconductor thin enough, you can get the magnetic field to penetrate in discrete quantities (this is real quantum physics now) called flux tubes (the blue lines that go through the disc).


Inside each of the magnetic flux tubes, the superconductivity is destroyed, but the superconductor tries to keep the magnetic tubes pinned in weak areas and any movement of the superconductor itself (like if you pushed it) causes the flux tubes to move, and this is what traps (or locks) the superconductor in midair.



If you’d like to experiment with superconductors yourself, check out this information.


Click here to go to next lesson on The difference between polarizing and charging.

The difference between polarizing and charging.

Wednesday November 5, 2014

Have you ever had a bad hair day? Did you happen to notice if the air was drier or wetter weather on those days? Usually folks have bad hair days when the air is drier, which is when static charge can build up more easily. Some folks notice every time they touch a doorknob, slide down a plastic slide, or scuff along the carpet in socks that they get zapped. Since there’s less water vapor in the air on drier days, there’s more of a chance for static charge to build up. The water molecule dissipates the static charge, and the more wet the air is (humid), the less static build up there is. Static electricity experiments are really hard to do on humid days, especially if it’s raining outside!
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Can you rub a balloon and stick it to the wall? Why does that work? The wall isn’t positively charged, is it?


No… the wall is not charged at all. It’s electrically neutral. However, when you bring a negatively charged balloon near it, two important things happen: the negative charge on the balloon repels the negative charges in the wall, pushing them further away. At the same time, the positive charges in the wall are attracted to the balloon and move toward it. The result is that the balloon sticks to the wall, and you have just moved charges around in the wall without even realizing it. Polarization means that you separate the charges in an object. The wall became polarized when you brought the balloon close to it.


Like charges repel and opposites attract.This happens in neutrally charged objects, like the yardstick in the electrostatic motor that you’ve done previously on this page. If the object is a conductor, like a metal, the charges move quickly from one side of the object to the other quite freely along the surface.


However if the object is an insulator, the electrons simply redistribute themselves within the atom, since the charges can’t move along the surface as they would with a conductor. The electrons live in an electron cloud that surrounds the nucleus of the atom, which normally is uniform and symmetrical. When an electrical charge is applied to insulators, that cloud will distort and become non-symmetrical as the electrons move in response.  In this way, insulators can be polarized.


Water is a polar molecule. In a molecule, the atoms stay together to form the molecule through bonds that are formed between the negative and positive charges on the individual atoms. For water, the oxygen  and hydrogen have a polar bond because the protons in one are attracted to the electrons in the other. The electrons are shared and their electron clouds overlap.


For water however, the electrons within the clouds are not equally shared which makes the electron cloud distorted, making one side of the water molecule more negatively electrically charged than the other. This makes water a polar molecule because the electron cloud is shifted more toward the oxygen than the hydrogen atoms.


When you bring a charged balloon near a thin trickle of water streaming from the faucet, the stream is deflected and sprayed by the presence of the balloon because the water molecules are polar and align to the balloon.


Just a quick tip: don’t mix up the concepts of polarizing and charging.  Charging is when there’s an imbalance of electric charge, like rubbing the balloon on your head. The balloon now has an excess number of electrons, so it’s negatively charged. Objects that are polarized have their charges separated either on the surface or within the atom itself. The overall charge of a polarized object is balanced (electrically neutral), even if the negative charges are at one end and positive charges are on the other.


Scientific Concepts for Atoms:


  • All matter is made of atoms.
  • An atom is the smallest part of stable matter.
  • Atoms rarely hang out alone. They join together in groups from two to millions of atoms.
  • Atoms are made of three basic particles. Neutrons, protons, and electrons.
  • Neutrons and protons are together in the middle of the atom and make up the nucleus of the atom. Electrons move around the nucleus. They don’t “orbit” the nucleus. Next lesson we will talk more about how they move. It’s one of the wacky things about electrons.
  • Atoms differ from one another by how many protons, neutrons, and electrons they have in them.
  • Elements are specific kinds of atoms. Every atom is a type of element.
  • There are over 112 elements. Ninety of which are found naturally. Twelve different elements are the major ingredients of over 90% of all matter. Five different elements are the major ingredients of all living things.
  • Carbon, Hydrogen, Oxygen, Nitrogen, and Calcium are the five main elements that make up all living matter.
  • Most atoms come from stars and have been around since the beginning of time.
  • Atoms get used, and reused again and again as things change over time.

Scientific Concepts for Electrons:


  • Electrons don’t orbit nuclei. They pop in and pop out of existence.
  • Electrons do tend to stay at a certain distance from a nucleus. This area that the electron tends to stay in is called a shell.
  • The electrons move so fast around the shell that the shell forms a balloon like ball around the nucleus.
  • An atom can have as many as seven shells.
  • The number of electrons an atom has determines how many shells it has.
  • A shell can only hold so many electrons. The number of electrons a shell can hold can be determined by the formula 2n2 where n is the number of the shell.
  • Atoms are “satisfied” if they have a full outer shell or if they have a multiple of eight electrons in their outer shell.
  • If an atom is not “satisfied” it will gladly share electrons with other atoms forming molecules.

Click here to go to next lesson on Charging Methods.

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Planetary and Satellite Motion

Wednesday November 5, 2014
Johannes Kepler, a German astronomer famous for his laws of planetary motion. Check out our Johannes Kepler facts page for more information.
Johannes Kepler, a German astronomer famous for his laws of planetary motion. Check out our Johannes Kepler facts page for more information.

Johannes Kepler, a German mathematician and astronomer in the 1600s, was one of the key players of his time in astronomy. Among his best discoveries was the development of three laws of planetary orbits. He worked for Tycho Brahe, who had logged huge volumes of astronomical data, which was later passed onto to Kepler. Kepler took this information to design and develop his ideas about the movements of the planets around the Sun.


Kepler’s 1st Law states that planetary orbits about the Sun are not circles, but rather ellipses. The Sun lies at one of the foci of the ellipse.


Well, almost.


Newton’s Laws of Motion state that the Sun can’t be stationary, because the Sun is pulling on the planet just as hard as the planet is pulling on the Sun. They are yanking on each other. The planet will move more due to this pulling because it is less massive. The real trick to understanding this law is that both objects orbit around a common point that is the center of mass for both objects. If you’ve ever swung a heavy bag of oranges around in a circle, you know that you have to lean back a bit to balance yourself as you swing around and around. It’s the same principle, just on a smaller scale.


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In our solar system the Sun has 99.85% of the mass, so the center of mass between the Sun and any other object actually lies inside the Sun (although not at the center).


Kepler’s 2nd Law states that a line connecting the Sun and an orbiting planet will sweep out equal areas in for a given amount of time. The planet’s speed decreases the further from the Sun it is located (actually, the speed varies inversely with the square‐root of the distance, but you needn’t worry about that).


You can see this for yourself by tying a ball to the end of a string and whirl it around in a circle. After a few revolutions, let the string wind itself up around your finger. As the string length shortens, the ball speeds up. As the planet moves inward, the planet’s orbital speed increases.


Embedded in the second law are two very important laws: conservation of angular moment and conservation of energy. Although those laws might sound scary, they are not difficult to understand. Angular momentum is distance multiplied by mass multiplied by speed. The angular momentum for one case must be the same for the second case (otherwise it wouldn’t be conserved). As the planet moves in closer to the Sun, the distance decreases. The speed it orbits the Sun must increase because the mass doesn’t change. Just like you saw when you wound the ball around your finger.


Energy is the sum of both the kinetic (moving) energy and the potential energy (this is the “could” energy, as in a ball dropped from a tower has more potential energy than a ball on the ground, because it “could” move if released). For conservation of energy, as the planet’s distance from the Sun increases, so does the gravitational potential energy. Again, since the energy for the first case must equal the energy from the second case (that’s what conservation means), the kinetic energy must decrease in order to keep the total energy sum a constant value.


Kepler’s 3rd Law is an equation that relates the revolution period with the average orbit speed.


The important thing to note here is that mass was not originally in this equation. Newton came along shortly after and did add in the total mass of the system, which fixed the small error with the equation. This makes sense, as you might imagine a Sun twice the size would cause the Earth to orbit faster. However, if we double the mass of the Earth, it does not affect the speed with which it orbits the Sun. Why not? Because the Earth is soooo much smaller than the Sun that increasing a planet’s size generally doesn’t make a difference in the orbital speed. If you’re working with two objects about the same size, of course, then changing one of the masses absolutely has an effect on the other.



Click here to go to next lesson on Fun Activity with Kepler’s Laws.

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Fun Activity with Kepler’s Laws

Wednesday November 5, 2014
Johannes Kepler, a German astronomer famous for his laws of planetary motion. Check out our Johannes Kepler facts page for more information.
Johannes Kepler, a German astronomer famous for his laws of planetary motion. Check out our Johannes Kepler facts page for more information.

Kepler’s Laws of planetary orbits explain why the planets move at the speeds they do. You’ll be making a scale model of the solar system and tracking orbital speeds.


Kepler’s 1st Law states that planetary orbits about the Sun are not circles, but rather ellipses. The Sun lies at one of the foci of the ellipse. Kepler’s 2nd Law states that a line connecting the Sun and an orbiting planet will sweep out equal areas in for a given amount of time. Translation: the further away a planet is from the Sun, the slower it goes.
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Download Student Worksheet & Exercises


What are the planets in our solar system starting closest to the Sun? On a sheet of paper, write down a planet and label it with the name. Do this for each of the eight planets.


  • Mercury is 0.39 AU (in a rocket it would take 2.7 months to go straight to Mercury from the Sun)
  • Venus is 0.72 AU
  • Earth is 1 AU (in a rocket it would take 7 months to go straight to Earth from the Sun)
  • Mars is 1.5 AU
  • Jupiter is 5.2 AU
  • Saturn is 9.6 AU
  • Uranus is 19.2 AU
  • Neptune is 30.1 AU (in a rocket it would take 18 years to go straight to Neptune from the Sun)

Of course, we don’t travel to planets  in straight lines – we use curved paths to make use of the gravitational pull of nearby objects to slingshot us forward and save on fuel.


  1. Now draw the location of the asteroid belt.
  2. Draw the position of the Kuiper Belt” and ask a student to draw and label it (beyond Neptune).
  3. Where are the five dwarf planets? They are in the Kuiper belt and the asteroid belt:
    • Ceres (in the Asteroid belt, closer to Jupiter than Mars)
    • Pluto (is 39.44 AU from the Sun)
    • Haumea (43.3 AU)
    • Makemake (45.8 AU)
    • Eris. (67.7 AU)

Now for the fun part! You’ll need a group of friends to work together for this lab, so you have at least one student for each planet, one for the Sun, and two for the asteroid belts, and five for the dwarf planets. You can assign additional students to be moons of Earth (Moon), Mars (Phobos and Deimos), Jupiter (assign only 4 for the largest ones: Ganymede, Callisto, Io, and Europa), Saturn (again, assign only 4: Titan, Rhea, Iapetus, and Dione), Uranus (Oberon, Titania), and Neptune (Triton). If you still have extra students, assign one to Charon (Pluto’s binary companion) and one each to Hydra and Nix, which orbit Pluto and Charon. While you ask the students to walk around in a later step, the moons can circle while they orbit.


  1. First, walk outside to a very large area.
  2. Hand the Sun student the measuring tape.
  3. Ask Kuiper Belt student(s) to take the end of the measuring tape and begin walking slowly away from the Sun.
  4. With each student assigned to the distance shown, grab the measuring tape and walk along with it. Please be careful – measuring tapes can have sharp edges! You can use gloves when you grab the tape if you’ve got a sharp steel measuring tape to protect your hands. Ask the Sun to call out the distances periodically so the students know when it’s time to come up.
  5. What do you notice about the distances between the planets? The nearest star is 114.5 miles away!
  6. Ask the students to let go of the measuring tape, except for Neptune and the Sun. Everyone else gathers around you (a safe distance away, as Neptune is going to orbit the Sun).
  7. Using a stopwatch, notice how much time it takes Neptune to walk around the Sun while holding the measuring tape taut. How long did it take for one revolution?
  8. Now ask Mercury to take their position on the tape at the appropriate distance. Time their revolution as they walk around the Sun. How long did it take?
  9. How does this relate to the data you just recorded for Neptune and Mercury? You should notice that the speeds the kids were walking at were probably nearly the same, but the time was much shorter for Mercury. If you could swing them around (instead of having them walk), can you imagine how this would make Mercury orbit at a faster speed than Neptune?
  10. If you have it, you can illustrate how Kepler’s 2nd law works and relate it back to this experiment. Tie a ball to the end of a string and whirling it around in a circle. After a few revolutions, let the string wind itself up around your finger. As the string length shortens, the ball speeds up. As the planet moves inward, the planet’s orbital speed increases. The planet’s speed decreases the further from the Sun it is located.
  11. Ask one of the bigger students to take their position with the measuring tape, reminding them to keep the tape taut no matter what happens. When they start to walk around the Sun, have the Sun move with them a bit (a couple of feet is good). Let the students know that the planet also yanks on the Sun just as hard as the Sun yanks on the planet. Since the planet is much smaller than the Sun, you won’t see as much motion with the Sun.
  12. Optional demonstration to illustrate this idea: take a heavy bag (I like to use oranges) and spin it around as you whirl around in a circle. Do you notice the student leans back a bit to balance themselves as they swing around and around? This is the same principle, just on a smaller scale. The two objects (the bag and the student) are orbiting around a common point, called the center of mass. In our real solar system, the Sun has 99.85% of the mass, so the center of mass lies inside the Sun (although not at the exact center).
  13. Look at the length of your measuring tape. Find the data table you need to use in the tables. Circle the one you’re going to use or cross out the ones you’re not.
  14. Using a stopwatch, time Venus as they walk around the Sun while holding the measuring tape taut. How long did it take for one revolution? (Make sure the Sun doesn’t move much during this process like they did for the demonstration. We’re assuming the Sun is at the center.)
  15. Continue this for all the planets.

What’s Going On?

Johannes Kepler, a German mathematician and astronomer in the 1600s, was one of the key players of his time in astronomy. Among his best discoveries was the development of three laws of planetary orbits. He worked for Tycho Brahe, who had logged huge volumes of astronomical data, which was later passed onto to Kepler. Kepler took this information to design and develop his ideas about the movements of the planets around the Sun.


Kepler’s 1st Law states that planetary orbits about the Sun are not circles, but rather ellipses. The Sun lies at one of the foci of the ellipse. Well, almost. Newton’s Laws of Motion state that the Sun can’t be stationary, because the Sun is pulling on the planet just as hard as the planet is pulling on the Sun. They are yanking on each other. The planet will move more due to this pulling because it is less massive. The real trick to understanding this law is that both objects orbit around a common point that is the center of mass for both objects. If you’ve ever swung a heavy bag of oranges around in a circle, you know that you have to lean back a bit to balance yourself as you swing around and around. It’s the same principle, just on a smaller scale.


In our solar system the Sun has 99.85% of the mass, so the center of mass between the Sun and any other object actually lies inside the Sun (although not at the center).


Kepler’s 2nd Law states that a line connecting the Sun and an orbiting planet will sweep out equal areas in for a given amount of time. The planet’s speed decreases the further from the Sun it is located (actually, the speed varies inversely with the square‐root of the distance, but you needn’t worry about that). You can demonstrate this to the students by tying a ball to the end of a string and whirl it around in a circle. After a few revolutions, let the string wind itself up around your finger. As the string length shortens, the ball speeds up. As the planet moves inward, the planet’s orbital speed increases.


Embedded in the second law are two very important laws: conservation of angular moment and conservation of energy. Although those laws might sound scary, they are not difficult to understand. Angular momentum is distance multiplied by mass multiplied by speed. The angular momentum for one case must be the same for the second case (otherwise it wouldn’t be conserved). As the planet moves in closer to the Sun, the distance decreases. The speed it orbits the Sun must increase because the mass doesn’t change. Just like you saw when you wound the ball around your finger.


Energy is the sum of both the kinetic (moving) energy and the potential energy (this is the “could” energy, as in a
ball dropped from a tower has more potential energy than a ball on the ground, because it “could” move if released). For conservation of energy, as the planet’s distance from the Sun increases, so does the gravitational potential energy. Again, since the energy for the first case must equal the energy from the second case (that’s what conservation means), the kinetic energy must decrease in order to keep the total energy sum a constant value.


Kepler’s 3rd Law is an equation that relates the revolution period with the average orbit speed. The important thing to note here is that mass was not originally in this equation. Newton came along shortly after and did add in the total mass of the system, which fixed the small error with the equation. This makes sense, as you might imagine a Sun twice the size would cause the Earth to orbit faster. However, if we double the mass of the Earth, it does not affect the speed with which it orbits the Sun. Why not? Because the Earth is soooo much smaller than the Sun that increasing a planet’s size generally doesn’t make a difference in the orbital speed. If you’re working with two objects about the same size, of course, then changing one of the masses absolutely has an effect on the other.


Exercises


  1.  If the Sun is not stationary in the center but rather gets tugged a couple of feet as the planet  yanks on it, how do you think this will affect the planet’s orbit?
  2.  If we double the mass of Mars, how do you think this will affects the orbital speed?
  3.  If Mercury’s orbit is normally 88 Earth days, how long do you estimate Neptune’s orbit to  be?

Click here to go to next lesson on Elliptical Orbits.

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Elliptical Orbits

Wednesday November 5, 2014

If one of Kepler’s Laws describe the orbits of satellites as being an elliptical orbit, you might be wondering what an ellipse is! Here’s a really neat way to make an ellipse using a pencil and a rubber band:



 


Click here to go to next lesson on Applying Kepler’s Laws.

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Applying Kepler’s Laws

Wednesday November 5, 2014

Let’s try a few practice problems so you get more familiar with how to use and apply Kepler’s Laws to real world physics problems…


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Click here to go to next lesson on Jupiter’s Moons.

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Jupiter’s Moons

Wednesday November 5, 2014

A satellite is an object that orbits the sun, earth or other massive body like a planet, moon, asteroid, or even galaxy. There are two kinds of satellites: natural, like the moon, and man-made, like the Hubble Space Telescope.


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Click here to go to next lesson on New Planets.

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New Planets

Wednesday November 5, 2014

But physics doesn’t care if a satellite is man-made or not. The laws of physics and math equations still apply no matter where the satellite came from.


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Click here to go to next lesson on Why Satellites Stay in Orbit.

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Why Satellites Stay in Orbit

Wednesday November 5, 2014

An important concept to understand is that a satellite is a projectile, meaning that only the force of gravity is acted on it (once it’s launched). In order to maintain it’s orbit, a satellite needs to fall continuously at the same rate that the earth is curving away from it.


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Click here to go to next lesson on Satellite Crash!

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Satellite Crash!

Wednesday November 5, 2014

The Hubble Space Telescope (HST) zooms around the Earth once every 90 minutes (about 5 miles per second), and in August 2008, Hubble completed 100,000 orbits! Although the HST was not the first space telescope, is the one of the largest and most publicized scientific instrument around. Hubble is a collaboration project between NASA and the ESA (European Space Agency), and is one of NASA’s “Great Observatories” (others include Compton Gamma Ray Observatory, Chandra X-Ray Observatory, and Spitzer Space Telescope). Anyone can apply for time on the telescope (you do not need to be affiliated with any academic institution or company), but it’s a tight squeeze to get on the schedule.


Hubble’s orbit zooms high in the upper atmosphere to steer clear of the obscuring haze of molecules in the sea of air. Hubble’s orbit slowly decays over time and begins to spiral back into Earth until the astronauts bump it back up into a higher orbit.


But how does a satellite stay in orbit? Try this experiment now:


Materials:


  • marble
  • paper
  • tape

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Download Student Worksheet & Exercises


Troubleshooting: Expect to find marbles flying everywhere with this experiment! This quick activity demonstrates the idea of centripetal (centrifugal) acceleration. What happens when you circle the cone too slow or too fast? The marble itself is the satellite (like HST), and the cone’s apex (tip) is the Earth. When the marble zooms around too slow, it falls back into the Earth. So what keeps it up in “orbit”?


The faster an object moves, the greater the acceleration against the force of gravity (toward the Earth in this case). Think back to the Physics lab – when a marble went too slow through the roller coaster loop, it crashed back to the floor. When it went too fast, it flew off the track. There was a certain speed that was needed for the marble to stay in the loop and on course. The same is true for satellites in outer space.


If you have trouble with this experiment, just replace the paper cone with a disposable cup with a lid and try again (with the lid in place), and see if you can keep the marble circling around the top rim.


Exercises


  1.  What happens when your marble satellite moves too slowly?
  2.  What happens when the marble satellite orbits too fast?
  3. What effect does changing the marble mass have on your satellite speed?
  4.  How is this model like the real thing?

Click here to go to next lesson on Saturn’s Moons.

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Saturn’s Moons

Wednesday November 5, 2014

Kepler’s Law of Periods relates the period T of any planet around the sun to the cube of the semi-major axis a of the orbit:


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If T is in earth years, a is in AU (1 AU = distance from the sun to the earth), and M = solar mass, then the equation above reduces to: T2 = a3.



 


Click here to go to next lesson on Orbits of Satellites.

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Orbits of Satellites

Wednesday November 5, 2014

A satellite is an object that does around a planet, a star, or other similar object. Here’s how you can figure out the net force of a satellite as well as the velocity of the satellite, since the only force applied to the satellite is from gravity:


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Click here to go to next lesson on Orbital Mechanics.

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Orbital Mechanics

Wednesday November 5, 2014

For a satellite orbiting around the earth at a given distance. What is the speed and acceleration of the satellite? Do you think you need to know the masses of the satellite and the earth, or just one?


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Click here to go to next lesson on Equations for Circular Motion.

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Equations for Circular Motion

Wednesday November 5, 2014

Here’s an overview of all the equations we’ve been using so far for our study in uniform circular motion:


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Click here to go to next lesson on How Fast is the Moon?

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How Fast is the Moon?

Wednesday November 5, 2014

How fast does the moon travel around the earth? And how far away is the moon really? Here’s a way to figure out!


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Click here to go to next lesson on Callisto.

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