Electromagnets Experiments & Videos

Special Science Teleclass: Magnetism

Saturday April 18, 2020

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!

Discover how to detect magnetic fields, learn about the Earth's 8 magnetic poles, and uncover the mysterious link between electricity and magnetism that marks one of the biggest discoveries of all science…ever.

Materials:

Box of paperclips
Two magnets (make sure one of them ceramic because we're going to break it)
Compass
Hammer
Nail
Sandpaper or nail file
D cell battery
Rubber band
Magnet Wire

Optional Materials if you want to make the Magnetic Rocket Ball Launcher:Four ½” (12mm) neodymium magnets

Nine ½” (12 mm) ball bearings
Toilet paper tube or paper towel tube
Ruler with groove down the middle
Eight strong rubber bands
Scissors

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Key Concepts

While the kids are playing with the experiments see if you can get them to notice these important ideas. When they can explain these concepts back to you (in their own words or with demonstrations), you’ll know that they’ve mastered the lesson.

Magnets

Magnetic fields are created by electrons moving in the same direction. Electrons can have a “left” or “right” spin. If an atom has more electrons spinning in one direction than in the other, that atom has a magnetic field.
If an object is filled with atoms that have an abundance of electrons spinning in the same direction, and if those atoms are lined up in the same direction, that object will have a magnetic force.
A field is an area around an electrical, magnetic or gravitational source that will create a force on another electrical, magnetic or gravitational source that comes within the reach of the field.
In fields, the closer something gets to the source of the field, the stronger the force of the field gets. This is called the inverse square law.
A magnetic field must come from a north pole of a magnet and go to a south pole of a magnet (or atoms that have turned to the magnetic field.)
All magnets have two poles. Magnets are called dipolar which means they have two poles. The two poles of a magnet are called north and south poles. The magnetic field comes from a north pole and goes to a south pole. Opposite poles will attract one another. Like poles will repel one another.
Iron and a few other types of atoms will turn to align themselves with the magnetic field. Over time iron atoms will align themselves with the force of the magnetic field.
The Earth has a huge magnetic field. The Earth has a weak magnetic force. The magnetic field comes from the moving electrons in the currents of the Earth’s molten core. The Earth has a north and a south magnetic pole which is different from the geographic north and south pole.
Compasses turn with the force of the magnetic field.

Electromagnetism

Electricity is moving electrons. Magnetism is caused by moving electrons. Electricity causes magnetism.
Magnetic fields can cause electricity.

What's Going On?

The scientific principles we’re going to cover were first discovered by a host of scientists in the 19^th century, each working on the ideas from each other, most prominently James Maxwell. This is one of the most exciting areas of science, because it includes one of the most important scientific discoveries of all time: how electricity and magnetism are connected. Before this discovery, people thought of electricity and magnetism as two separate things. When scientists realized that not only were they linked together, but that one causes the other, that’s when the field of physics really took off.

Questions

When you’ve worked through most of the experiments ask your kids these questions and see how they do:

How many poles do magnets have, and what are they?
What happens when you bring two like poles together?
How do I know which pole is which on a magnet?
Is the magnetic force stronger or weaker the closer a magnet gets to another magnet?
What kinds of materials are magnets made from?
Name three objects that stick to a magnet.
Name three that don’t stick to a magnet.
What does a compass detect? How do you know when it’s detected it?

Answers:

How many poles do magnets have, and what are they? Two. North and South poles.
What happens when you bring two like poles together? They repel each other.
How do I know which pole is which on a magnet? Put two magnets together and find the spot where they are repelling the strongest. The poles facing each other are the same. Or bring it close to a compass. If the magnet attracts the needle to north, then the magnet’s pole is the south pole.
Is the magnetic force stronger or weaker the closer a magnet gets to another magnet? Stronger.
What kinds of materials are magnets made from? Iron, nickel and cobalt.
Name three objects that stick to a magnet. Paperclips, pipe cleaners, and staples.
Name three that don’t stick to a magnet. US quarter, glass, plastic.
What does a compass detect? How do you know when it’s detected it? The direction of a magnetic field. When the needle is deflected, the compass is in a magnetic field.

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Electromagnetic Crane

Sunday April 13, 2014

An electromagnet is a magnet you can turn on and off using electricity. By hooking up a coil of wire up to a battery, you will create an electromagnet. When you disconnect it, it turns back into a coil of wire. Since moving electrons cause a magnetic field, when connecting the two ends of your wire up to the battery, you caused the electrons in the wire to move through the wire in one direction. Since many electrons are moving in one direction, you get a magnetic field!
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Materials:

Nail
Wood skewer
Magnet wire
D cell battery
Sandpaper or nail file
2 rubber bands
Foam block
2 fat popsicle sticks
Paperclips
Drill
Hot glue or tape

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Galvanometers

Sunday April 4, 2010

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

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?
How does a moving magnet make electricity?
What makes the compass needle deflect in the second coil?
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?

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Electromagnet

Sunday April 4, 2010

After you’ve completed the galvanometer experiment, try this one!

You can wrap wire around an iron core (like a nail), which will intensify the effect and magnetize the nail enough for you to pick up paperclips when it’s hooked up. See how many you can lift!

You can wrap the wire around your nail using a drill or by hand. In the picture to the left, there are two things wrong: you need way more wire than they have wrapped around that nail, and it does not need to be neat and tidy. So grab your spool and wrap as much as you can – the more turns you have around the nail, the stronger the magnet.

(We included this picture because there are so many like this in text books, and it’s quite misleading! This image is supposed to represent the thing you’re going to build, not be an actual photo of the finished product.)

Find these materials:

Batteries in a battery holder with alligator clip wires
A nail that can be picked up by a magnet
At least 3 feet of insulated wire (magnet wire works best but others will work okay)
Paper Clips
Masking Tape
Compass

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1. Take your wire and remove about an inch of insulation from both ends. (Use sandpaper if you’re using magnet wire.)

2. Wrap your wire many, many times around the nail. The more times you wrap the wire, the stronger the electromagnet will be. Be sure to always wrap in the same direction. If you start wrapping clockwise, for example, be sure to keep wrapping clockwise.

3. Now connect one end of your wire to one terminal of the battery using an alligator clip (just like we did in the circuits from Unit 10).

4. Lastly, connect the other end of the wire to the other terminal of the battery using a second alligator clip lead to connect the electromagnet wire to the battery wire. This is where the wire may begin to heat up, so be careful.

5. Move your compass around your electromagnet. Does it affect the compass?

6. See if your electromagnet can pick up paper clips.

7. Switch the wires from one terminal of the battery to the other. Electricity is now moving in the opposite direction from the direction it was moving in before. Try the compass again. Do you see a change in which end of the nail the north side of the compass points to?

What happened there? By hooking that coil of wire up to the battery, you created an electromagnet. Remember, that moving electrons causes a magnetic field. Well, by connecting the two ends of your wire up to the battery, you caused the electrons in the wire to move through the wire in one direction.

Since many electrons are moving in one direction, you get a magnetic field! The nail helps to focus the field and strengthen it. In fact, if you could see the atoms inside the nail, you would be able to see them turn to align themselves with the magnetic field created by the electrons moving through the wire. You might want to test the nail by itself now that you’ve done the experiment. You may have caused it to become a permanent magnet!
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How Generators Work

Sunday April 4, 2010

Have you noticed that stuff sticks to your motor? If you drag your motor through a pile of paperclips, a few will get stuck to the side. What’s going on?

Inside your motor are permanent magnets (red and blue things in the photo) and an electromagnet (the copper thing wrapped around the middle). Normally, you’d hook up a battery to the two tabs (terminals) at the back of the motor, and your shaft would spin.

However, if you spin the motor shaft with your fingers, you’ll generate electricity at the terminals. But how is that possible? That’s what this experiment is all about.

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Materials:

9-18V DC motor
LED (bi-polar)

If you move a magnet along the length of a wire, it will create a very faint bit of electricity inside the wire. 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 past the wire.

A motor has a coil of wire wrapped around a central axis, so instead of rubbing back and forth (which is tough to going fast enough, because you have to stop, reverse direction, and start moving again every so often), it rotates past a set of magnets continuously.

When you add a battery pack to the motor terminals at the back, you energize the coil inside the motor, and it begins to rotate to attempt to line up its north and south poles. But the magnets are lined up in a way that it will continually ‘miss’ and overshoot, which keeps the shaft spinning over and over, faster and faster.

You can turn your motor into a generator by simply giving the shaft a quick spin with your fingers. Remember that attached to this shaft is a coil of wire. When you spin the shaft, you’re also moving a coil of wire past the permanent magnets inside to motor, which will create electricity in your coil and out the terminals.

You can attach a low-voltage LED directly to the motor terminals and spin the shaft to see the LED light up. Depending on the size of the magnets inside your motor, you may need to spin the shaft super fast to see the LED light up. The larger the motor, the easier this activity is. Try using a larger, 12V DC motor from the main shopping list for this section.

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Quick ‘n’ Easy DC Motor

Sunday April 4, 2010

Find a spare magnet – one you really don’t care about. Bring it up close to another magnet to find where the north and south poles are on the spare magnet. Did you find them? Mark the spots with a pen – put a N for north, and a S for south. Now break the spare magnet in half, separating the north from the south pole. (This might take a bit of muscle!) You should have one half be a north magnet, and the other a south. Or do you?

One of the big mysteries of the universe is why we can’t separate the north from the south end of a magnet. No matter how small you break that magnet down, you’ll still get one side that’s attracted to the north and the other that’s repelled. There’s just no way around this!

If you COULD separate the north from the south pole, you could point a magnet’s south pole toward your now-separated north pole, and it would always be repelled, no matter what orientation it rotated to. (Normally, as soon as the magnet is repelled, it twists around and lines up the opposite pole and snap! There go your fingers.) But if it were always repelled, you could chase it around the room or stick a pin through it so it would constantly move and rotate.

Well, what if we sneakily use electromagnetism? Note that you can use a metal screw, ball bearing, or other metal object that easily rotates. If your metal ball bearing is also magnetic, you can combine both the screw and the magnet together.

Famous scientist Michael Faraday built the first one of these while studying magnetic and electricity, and how they both fit together. What to see what he figured out?

Here’s what you do:

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Materials:

AA battery
small screw
wire (stripped on both ends)
very strong magnet (disc-shaped)

Download Student Worksheet & Exercises

Note: In case you missed it on the shopping list, you can order the disc magnet here.

The current from the battery is flowing through the wire, creating a magnetic field around the wire, which interacts with the magnetic field in the gold disk magnet. Since the wire creates a magnetic field that is perpendicular to the field in the gold magnet, the magnet feels a push, which causes it to rotate. Watch your fingers on this experiment – if you’re not careful and leave your wire contacting the magnet too long, you’ll roast your battery (and that’s really bad).

Exercises

How does this experiment work?
What happens if you reverse the polarity and attach the screw to the negative side of the battery?
How do you get your motor to spin the fastest?

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Relays & Homemade Shockers

Sunday April 4, 2010

This experiment is for advanced students. If you’ve attempted the relay and telegraph experiment, you already know it’s one of the hardest ones in this unit, as the gap needs to be *just right* in order for it to work. It’s a super-tricky experiment that can leave you frustrated and losing hope that you’ll ever get the hang of this magnetism thing.

Fear not, young scientist! Here’s a MUCH simpler relay experiment that will actually give a nice blue spark when fired up, along with a nice zap to the hand that touches it in just the right spot. You can also use this relay in your electricity experiments as a switch you can use to turn things on and off using electricity (instead of your fingers moving a switch), including how to make a latching burglar alarm circuit.

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Materials:

one relay
AA case
2 AA batteries
9V battery with clip (watch video)
alligator wires

Here’s what you need to do:

Download Student Worksheet & Exercises

Exercises

Is there a permanent magnet and/or an electromagnet inside a relay?
What makes the relay a switch?
What makes the relay turn on and off (*click*)?
Is the same power source that activates the relay also used for the circuit it’s switching?

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Relays and Telegraphs

Sunday April 4, 2010

Relays are telegraphs, and they both are basically “electrical switches”. This means you can turn something on and off without touching it – you can use electricity to switch something else on or off!

We’re going to build our own relay that will attract a strip of metal to make our telegraph ‘click’ each time we energize the coil.

IMPORTANT! This experiment is very tricky to get working right. You’ll want to pair up with someone who’s handy in the workshop and has a keen eye and a feather touch for adjusting the clicker in the final step. Someone who is a patient, fix-it type of person will be able to help you get this project working well.

Note: There are bonus experiment ideas near the bottom once you’ve mastered this activity.

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Materials:

block of foam
sandpaper
alligator wires
battery case
AA batteries
film canister or similar
nail
thin magnet wire (26-28g)
brass fasteners
1/2″ strip from a soup can for the clicker (watch video)
paper clip
hot glue gun
scissors
tape

Download Student Worksheet & Exercises

1. Make the electromagnet first (the nail turns into a magnet when you add power to the wire): Carefully unwrap your wire and stretch it into a long length. Cut it roughly in half, reserving one half for the next experiment.

2. Wrap the thin insulated wire (called ‘magnet wire’) around the nail. (More wraps mean more power for your magnet, so use a lot!) You can insert a nail into a drill and wind it on slow speed, too. Sand the insulation off the end leads. (We do this so you can attach things to the exposed metal part.)

3. Insert the AA batteries into their case. Using alligator clips, clip onto a brass fastener and insert it into the foam.

4. Attach the other end of the clip lead to the positive battery terminal. Bend a paperclip into a “V” shape. Wind the free end of the exposed metal of the electromagnet wire around another brass fastener and insert through the tip of the “V” shape and into the foam, opened up on other side.

5. Be sure the smaller side of the “V” rests on the foam such that it does not reach the first brass fastener; but the larger side of the “V”, when pressed down, does. (You just made a switch!)

6. Stick the electromagnet pointy-end down into the foam. If it wiggles around, you will need to hot glue it into place later. Wiggling is good for now. Hot glue one end of the clicker (narrow steel strip) to the top of a film canister.

7. Attach the film canister with hot glue, making sure the tip of the clicker is over the nail head. Do not glue the lid to the canister! (It’s a big plus to have it rotate and be adjustable.) Be sure that the electromagnet and nail have a tiny clearance between the nail head and the metal strip. Push your switch to the “ON” position, and the electromagnet should click accordingly!

Troubleshooting: If it doesn’t click, move your electromagnet up or down, changing the nail-head-to-clicker distance until it clicks! If it sticks, it’s too close. If it doesn’t move at all, it’s too far away. Hot glue nail into right position. (Clicker is bendable, too—for future adjustments.)

Take your time – this is a project that requires patience and observation to figure out what’s going on. If you’re frustrated, STOP, try another experiment, and return back later. For a more permanent project, use a small block of wood instead of the foam and hammer in your nail.

Still struggling? Then click here to try an easier relay experiment with shocking results.

Why does this work? Anytime you run electricity through a wire, a magnetic field shows up. We’re multiplying this effect when we coil the wire around a nail. A nail with wire wrapped around it is called an electromagnet. Think of it like a magnet you can turn on and off.

Using a paper-clip switch, we can turn the electricity on and send it through the electromagnet, turning the ordinary nail and wire into a magnet. When we release the paper-clip switch, the current (electricity) stops flowing and our electromagnet turns back into ordinary nail and wire.

When the electromagnet is energized (magnetized), it attracts the metal strip, which causes it to click downwards. Release the paper-clip switch, and the strip is no longer attracted to the nail (because it’s no longer a magnet).

When the switch is on, it’s a magnet. When it’s off, it’s not a magnet. Magnets attract steel, and that’s why the strip bends and clicks. It’s amazing we could communicate over thousands of miles this way, but we did!

For Advanced Students Only!

If you’ve got the relay working and you want more… we’ve got one for you! Dual relays are often called “repeaters”. They take an incoming signal and “repeat” the signal and send it out. You’ll find uses for this when you want to increase the signal strength – you detect the weaker, older one and repeat out a newer, stronger signal identical to it. When radio signals need to traverse long distances, this is the basic idea of how they do it on high mountaintops.

Here’s how you can make your own:

1. Make a telegraph with a switch (previous experiment) first, then make a second telegraph, without the switch, on a new foam slab. Here’s what you do for the telegraph without the switch:

2. The second electromagnet uses the first relay as a switch. One end of the electromagnet goes to the negative battery terminal (don’t forget to sand the magnet wire first!).

3. Connect the positive wire lead to the first telegraph’s ‘clicker’ piece. Wrap it around securely. If it doesn’t stick, wrap the wire onto a paperclip then clip it to the clicker.

4. Connect the second (sanded) electromagnet wire to the first telegraph’s Nail. (It must touch the nail part, not the wire part, in order to work correctly!) Click the switch! The switch controls BOTH relays now. If you make the wires between the two foam slabs longer (say, 50 feet), you could relay messages back and forth!

Troubleshooting Relays: If a clicker doesn’t work, check the clearance. Move the electromagnet up and down, until you find the perfect clicking spot. It needs to be close enough to click, but far enough so it won’t stick.

Can you make several ‘repeaters’? Repeaters are telegraphs (relays) that get switched on by each other (after an initial input from you). Can you connect three or four telegraphs together so that they get switched on in sequence?

Exercises

Why does the soup can clicker move?
Does this circuit use a permanent or electromagnet?
Why do we need multiple turns around a nail? Why not just a couple wraps?
What is the paper-clip switch used for?
How can a relay be used in real life? Give three examples.

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Homemade DC Motor

Sunday April 4, 2010

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!

This next activity mystifies even the most scientifically educated! Here’s what you need:

Materials:

magnet
magnet wire (26g works well)
D cell battery
two paper clips (try to find the ones shown in the video, or else bend your own with pliers)
sandpaper
fat rubber band

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1. Start out by winding the magnet wire around a D-cell battery 12-15 times. Coil the wire around the circular loop to keep the wires together. Be sure that the “ears” are straight (see photo below). This is now your ‘rotor’:

2. IMPORTANT! Remove the insulation by sanding the entire length of both “ears”, flip the rotor over, and sand only one “ear” side, leaving the insulation intact on the side of the remaining “ear”.

3. Wrap the rubber band around the battery long-ways. Untwist a paper clip to make the shape shown in the video.

4. Make two of these paper clip shapes. You can use pliers to help make the shape. Place the left end under the rubber band in the center of the each end. The loop on the right end is where the rotor will hang (you can flip it over or bend accordingly if it falls out too much.)

5. Slide the rotor into the loops.

6. Place the magnet on the battery just under the rotor under the rubber band (you can use an additional rubber band to secure if needed). You want the rotor to be as close to the magnet as possible without hitting it. Give it a spin, and you’re off!

Troubleshooting: Usually problems arise when checking the connection between the battery and paper clips. Hold the battery with the fingertips in the center of each battery end and squeeze to make a good connection. If it still fails to spin, check your rotor: one ear should be insulation-free, the other should have a stripe of insulation down its length.

If you’re still having trouble, check the ears to be sure they are straight. The rotor needs to be able to spin nicely, so ensure it is well-balanced. Egg-shaped rotors just won’t turn.

Wow! How does THAT work? When you run electricity through any wire, it turns slightly into a magnet. When you stack wires on top of each other (as you did with the coil of wire), you multiply this effect and get a bigger magnet.

For the DC motor: The coil of wire is the O-shaped ring. When the sanded parts of the “ears” are connected to the paper clip, current flows through the circuit. When this happens, everything connects together and turns the coil wire into an electromagnet, which is then attracted to the magnet on the battery.

When the O-ring rotates, it moves around until the un-sanded portion breaks the connection and turns it back into just a coil of wire. The coil continues to float around in a circle until it hits the sanded parts again, which re-energizes the coil, turning it back into an electromagnet, which is now attracted to the magnet on the battery, which pulls it around again…and round it goes!

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Hearing Magnetism

Sunday April 4, 2010

Want to hear your magnets? We’re going to use electromagnetism to learn how you can listen to your physics lesson, and you’ll be surprised at how common this principle is in your everyday life. This project is for advanced students.

We’re going to invert the ideas used when we created our homemade speakers into a basic microphone. Although you won’t be able to record with this microphone, it will show you how the basics of a microphone and amplifier work, and how to turn sound waves back into electrical signals. You’ll be using the amplifier and your spare audio plug from the Laser Communicator for this project.

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Materials:

magnet wire
drill (or wind by hand)
nail
magnet
amplifier (see shopping list for info on where to get one)
audio plug

Download Student Worksheet & Exercises

An amplifier’s job is to take small electrical voltages (AKA the ‘input) and make them bigger (amplify them). Then, we usually plug a speaker or headphones into the amplifier and those turn the bigger electrical signal (AKA the ‘output’) into sound. So any small voltage that we plug into the amplifier’s input will get larger and then turn into sound through the built-in speaker.

One way to show this is to use a coil of wire and a magnet. If you take a coil of wire and move a magnet past, around, or through it, you will create a small electrical voltage (and current) in the wire. In fact, if you have enough wire and a big enough magnet, and move the magnet fast enough, the electricity coming out of the coil of wire can light up a light bulb (this is how an electric generator works).

So back to the amplifier: if we take the voltage from our little coil/magnet generator, and we put it into the amplifier, we’ll hear the sound from the speaker each time it makes a voltage. If we move the magnet back and forth really fast, we’ll hear a fast clicking sound. And if we were to move it super-incredibly-fast (faster than you could with your hands), then those clicks would blend together into a tone. Tones like this are what all sounds are made of.

In fact, this is exactly what a microphone does. Many microphones have a magnet and a coil of wire attached to a very thin piece of plastic or metal that vibrates when sound waves hit it. The plastic (or metal) in turn moves the coil of wire next to the magnet super-fast. Then this causes the electric voltage to come out of the coil and if you plug it into an amplifier it will make the same sound that the microphone heard, only louder.

Exercises

Why does the electromagnet make sound when you bring the permanent magnet close to it?
How is this like a microphone?
What did the aluminum do to the electromagnet?

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Rail Accelerator

Sunday April 4, 2010

We’re going to build on the quick ‘n’ easy DC motor to make a tiny rail accelerator (any larger, and you’ll need a power plant and a firing range and a healthy dose of ethics.) So let’s stick to the physics of what’s going on in this super-cool electromagnetism project. This project is for advanced students.

Here’s what we’re going to do:

We’re going to create two magnetic fields at right angles (perpendicular) to each other. When this happens, it causes things to move, spin, rotate, and roll out of the way. We’re going to focus this down to making a tiny set of wheel zip down a track powered only by magnetism. Ready?

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Materials:

cardboard
aluminum foil
hot glue
scissors
paper clip or wire coat hanger
two very small, strong disc magnets
9V battery with clip
2 alligator clip leads
pliers

Download Student Worksheet & Exercises

Did you notice how this rail accelerator is really just two of the ‘quick ‘n’ easy DC motors connected together? The wire is now the aluminum rail, and the magnetic field in the rail create a force perpendicular gold disk’s magnetic field. These two magnetic fields interact, causing the little wheels to roll. Which is why if you have the wheels on ‘backwards’ (or your battery connected backwards), your wheels will roll toward (instead of away) from you.

Troubleshooting: If you drop your wheels from too high up, you’ll knock the axle off-center and the wheels won’t roll. If your wheels still don’t roll, flip one of the magnets around (they must be in opposite directions for this to work!). Also make sure you’ve got a fresh 9V battery and good electrical connection between your clips and the track.

Exercises

Do the magnets need to be opposite in order for this to work?
Why do the wheels move?
Which track works the best?

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For Advanced Students Only!