Lesson 1: Magnets

Special Science Teleclass: Magnetism

Monday October 20, 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!

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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Ferrofluid

Friday July 1, 2011

A ferrofluid becomes strongly magnetized when placed in a magnetic field. This liquid is made up of very tiny (10 nanometers or less) particles coated with anti-clumping surfactants and then mixed with water (or solvents). These particles don’t “settle out” but rather remain suspended in the fluid.

The particles themselves are made up of either magnetite, hematite or iron-type substance.

Ferrofluids don’t stay magnetized when you remove the magnetic field, which makes them “super-paramagnets” rather than ferromagnets. Ferrofluids also lose their magnetic properties at and above their Curie temperature points.

Ferrofluids are what scientists call “colloidal suspensions”, which means that the substance has properties of both solid metal and liquid water (or oil), and it can change phase easily between the two. (We as show you this in the video below.) Because ferrofluids can change phases when a magnetic field is applied, you’ll find ferrofluids used as seals, lubricants, and many other engineering-related uses.

Here’s a video on toner cartridges and how to make your own homemade ferrofluid. It’s a bit longer than our usual video, but we thought you’d enjoy the extra content.

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Download Student Worksheet & Exercises

Engineering and scientists use ferrofluids to make a liquid seal in hard disks around the spinning disks to keep out dust and grit (hard drives must be kept exceptionally clean!). They do this by adding a layer of ferrofluid between the rotating shaft and magnets which surround the shaft.

You can also use ferrofluids to reduce friction, the way ice and water are used in ice skating rinks. If you coat a strong magnet with ferrofluid, you can get it to glide across a smooth surface like a hockey puck.

NASA uses ferrofluids in the flight instruments for spacecraft, also!

Each particle of ferrofluid is like a each grain or a micro-magnet, which not only interacts with magnetic fields, but also with light.

With loudspeakers, the large magnets that interacting with the coil often heat up. If we replace the magnet with ferrofluid (which is a liquid, remember!) it will actively conduct the heat away from the coil and cool it down because cold ferrofluid is more strongly attracted than hot, and thus the cooler fluid flows toward the coil, and the warmer fluid moves away from the coil.

Exercises

Is the ferrofluid a solid or a liquid?
Does the strength of a magnet matter?
What would happen if the magnet went over the rim of the cup?
Does the ferrofluid have a north and south pole?
What happens if you bring a compass near the ferrofluid?
Name three specific ways ferrofluid makes our lives easier. How might you use a ferrofluid if you were inventing something?

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Magnets Exercises

Sunday April 4, 2010

Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.

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1. What happens when you break a magnet in half? Can you separate the North and South poles?
2. What causes magnetism?
3. Why does your refrigerator magnet stick to the fridge door?
4. Is aluminum magnetic, electrically conductive, or both?
5. What elements would you guess to be in a magnet? Can you name three?
6. What causes (or creates) magnetic field?
7. Name the biggest magnet you can think of.
8. Where is the magnetic south pole?
9. What happens when you heat up a magnet?
10. Why is the grape repelled by the magnet?
11. Why does the magnet go slowly down the ramp?

Need answers?

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Answers to Magnets Exercises

Sunday April 4, 2010

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!

Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.

Answers:
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1. You get two smaller magnets, each with their own north and south pole. You cannot separate the north and south pole of a manget.

2. Electrons. More accurately, a majority of electrons moving in a similar direction creates a magnetic field.

3. Electrons move on their own. They move around the nucleus and they spin. It’s the electron spin that tends to be responsible for the magnetic field in those “permanent” magnets (the magnets that maintain a magnetic field without electricity flowing).

4. Aluminum conducts electricity, but is not magnetic as detectable by the human eye (called ferromagnetic). Aluminum is technically paramagnetic (very weakly attracted to both poles of a magnet).

5. Iron, nickel, and cobalt are ferromagnetic (attracted to both poles of the magnet).

6. A magnetic field is something I can’t tell you about – it just is (like gravity). Best thing I can do is tell you that 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.

7. The earth. On a universe-scale, magnetars (magnetized neutron stars) are the biggest known magnets out there.

8. Off the coast of Antarctica in the ocean.

9. When you heat a magnet past the ‘Curie Temperature’, the magnet loses its magnetism. Once cooled back down, it will regain magnetism again.

10. The grape contains sugar water, which is diamagnetic (repelled by both poles).

11. The eddy currents in the metal plate created by the moving (sliding) magnet slow down the magnet and counteracts gravity.

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Eddy Currents and Magnetic Brakes

Sunday April 4, 2010

Eddy currents defy gravity and let you float a magnet in midair. Think of eddy currents as brakes for magnets. Roller coasters use them to slow down fast-moving cars on tracks and in free-fall elevator-type rides.

Here’s what you need to do this activity:

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Find a thick piece of metal, like copper or aluminum to work with your neodymium magnets.

Materials:

aluminum block (the thicker the better, although you can try a cookie sheet)
neodymium disc magnets

When you have your parts, you can watch the video:

What’s going on? Here’s the basic idea: when a magnet moves near an object that conducts electricity (usually metal), it creates electric currents called eddy currents which start to flow in the conductor. These eddy currents create magnetic fields (electricity causes magnetism, remember?) in the opposite direction of the moving magnet, slowing an object down so it appears to float.

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Which way is North?

Sunday April 4, 2010

I can still remember in 2nd grade science class wondering about this idea. And I still remember how baffled my teacher was when I asked her this question: “Doesn’t the north tip of a compass needle point to the south pole?” Think about this – if you hold up a magnet by a string, just like the needle of a compass, does the north end of the magnet line up with the north or south pole of the earth?

If you remember about magnets, you know that opposite attract. So the north tip of the compass will line up with the Earth’s SOUTH pole. So compasses are upside-down! Here’s an activity you can do right now…
Materials:

magnet
compass
string

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Download Student Worksheet & Exercises

The magnetic pole which was attracted to the Earth’s north pole was labeled as the Boreal or “north-seeking pole” in the 1200s, which was later shortened to “north pole”. To add to the confusion, geologists call this pole the North Magnetic Pole.

Exercises

How are the lines of force different for the two magnets?
How far out (in inches measured from the magnet) does the magnet affect the compass?
What makes the compass move around?
Do you think the compass’s north–south indicator is flipped, or the Earth’s North Pole where the South Pole is? How do you know?

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Bouncing Magnets

Sunday April 4, 2010

Want to see a really neat way to get magnetic fields to interact with each other? While levitating objects is hard, bouncing them in invisible magnetic fields is easy. In this video, you’ll see how you can take two, three, or even four magnets and have them perform for you.

Are you ready?

Materials:

3 identical magnets

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Download Student Worksheet & Exercises

Did you notice that if the north pole of the bottom magnet is up, then the south pole of the magnet stacked above it will be down? The stack holds together because opposites attract (north-south). You probably already knew that, right? But notice when you pull the top magnet to the side the bottom south face is repelled into the air above the north face of the fixed magnet. So what gives?

Remember that a magnet isn’t strictly north or south. There are field lines that connect the two poles. The field lines start at one end and swoop down to the other and back again like in this picture to the left, reversing from north to south as it does so. This is why the south face is repelled – because it’s actually the magnetic fields that are doing the repelling.

You can adjust your two bouncing magnets to have nearly the same ‘bouncy’ (frequency) by changing their distance apart. Notice that when one magnet starts bouncing, the magnetic field changes, which pushes and pulls on the other magnet. The two magnets interact with each other through their magnetic fields, pushing and pulling each other into resonance.

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

Once you’ve mastered two magnets, why not try three? Or four? What happens when you bring a conductor, like a thick sheet of copper, aluminum (cookie sheet or cake pan) nearby? The eddy currents created in the metal by the moving magnet created an opposing magnetic field that work to ‘brake’ the moving magnet and stop it from bouncing.

While this activity may seem a bit trivial (and a little fun), the idea of a magnetic field is one of the greatest leaps ever made in science. Scientist Michael Faraday imagined the idea that a magnet had not only a magnetic field, but that it cold push and pull on other magnets and moving electric charges. This crazy idea was so wild that it took many scientists a lifetime to come to terms with it… as it replaced an older idea from Newton that had stood for centuries.

And, as usually happens when someone has a new bright idea, others are quick to add to it. Shortly after Faraday’s idea about magnetic fields and electrical charges, Maxwell combined complicated mathematics (stuff you’ll only see at a university) into his four famous equations (Maxwell’s Equations) that describe all electric and magnetic fields.

Exercises

Why does the magnet float?
After you tap the floating magnet, does it vibrate for a short or long time? Why?
Why do we stack the magnets first before trying to levitate them?
How many magnets can you get to interact while floating?
When you float two magnets above the main magnet, how do the floating magnets interact with each other? Why do they do that?

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Magnetic Fields

Sunday April 4, 2010

This is a quick and simple experiment to answer the question of magnetic field strength: Do four magnets have a stronger magnetic pull than one? You’ll find the answer quite surprising… which is: it depends. Here’s what you need to do to see for yourself:

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Materials:

stack of round magnets (7-9)
film canisters (or small containers like M&M containers)
clay or foam or tissue

Download Student Worksheet & Exercises

What’s going on here? When you bring the bottoms of the two film canisters together, you can feel the force of repulsion (if not, flip one of the stacks inside one of the the canisters). While you’ll definitely notice that the force of 4-on-4 magnets is larger than 1-on-1, you won’t be able to tell the difference between 4-on-1 or 1-on-4. Or, put more simply, you can’t tell which has one magnet and which has four. So what’s going on?

The more magnets you have, the more magnetic force they exert. The magnetic forces between two stacks of ten magnets magnets are equal and opposite. The magnetic force exerted by a stack of two magnets and five magnets is also equal and opposite, although somewhat less than the stack of ten.

It’s the same with gravity – the force of gravity between two masses (like the sun and the Earth) is also equal and opposite – or the earth would get pulled into the sun or go flying out of the solar system. The Earth exerts the same pull on the sun as the sun exerts on the Earth.

Say WHAT?!?

Did you expect four magnets to push with four times the force on the single magnet? That’s what common sense tells us. However, think of it this way: the 2nd, 3rd, and 4th magnets magnets are further away than the 1st magnet and so they each exert less and less of a push on the single magnet.

Exercises:

Why can’t you simply rub the needle back and forth with the magnet? Why do you have to stroke it in one direction?
What other objects/materials can you use to make a compass?
How do you know that the needle is magnetized?
Why did we float the needle in water?

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Magnetic Sensors

Sunday April 4, 2010

Wouldn’t it be cool to have an alarm sound each time someone opened your door, lunch box, or secret drawer? It’s easy when you use a reed switch in your circuit! All you need to do it substitute this sensor for the trip wire and you’ll have a magnetic burglar alarm.

The first thing you need to do is get your reed switch out, because we have to tear into it in order to get the part we need. Here’s what you need:

Materials:

reed switch
magnet
LED
AA case
2 alligator wires
2 AA batteries

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Download Student Worksheet & Exercises

Exercises

Where does the magnet need to be located in order for your circuit to work?
How does the switch work? Draw a picture and label the parts that make it work in the circuit.
Can the switch be activated through the side of a drawer, so that the switch is in the inside and the magnet is on the outside?
Which way does the magnet activate the switch the best? How are the poles oriented relative to the switch?

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Magnet Boats

Sunday April 4, 2010

We took our first step into the strange world of magnetism when we played with magnetizing a nail. We learned that magnets do what they do because of the behavior of electrons. When a bunch of those crazy little guys get going in the same direction they create a magnetic field. So what’s a magnetic field, you ask? That’s what this experiment is all about.

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As the North and South sides of a magnet get closer together, the pull of the magnetic force is stronger. This is typical of fields. The closer you get, the stronger the pull of the force gets. The farther you get, the weaker the pull of the force gets.

Materials:

shallow dish or bathtub
water
foam blocks (or milk jug lids)
stack of 6-10 magnets
hot glue gun

Download Student Worksheet & Exercises

When you build the little boats, remember that you kept the poles all the same (all north pointed up, for example). The floating magnets repel each other because they have the same pole oriented up. But notice that when you bring the larger magnet close, they are all attracted to it and also make geometric patterns! When you bring the larger magnet in closer, the size of your pattern changes, doesn’t it? Most patterns have at least one (sometimes two) stable patterns, each of which is a local minimum energy pattern. The patterns that the little boats make are very similar to the crystal structures in solids.

Notice how the magnet boats repel each other when they get too close, yet the hold each other in a pattern. Atoms do the same thing – they repel each other when you try to squish them together, yet hold together to form molecules.

Exercises

What shape do three magnets give? Why is this different from the shape that four magnets make?
Why do the magnets flip over when you first place them in the water?
How many magnets make a hexagon?
How is this experiment like the compass experiments we’ve done so far?
Why do the boats repel each other, yet still hold in a pattern?

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Simple Magnet Experiments

Sunday April 4, 2010

Let’s play around with the idea of lining up all the mini-magnets inside an object to magnetize it. You’ll need a steel nail (steel is a combination of iron and carbon), a magnet (the stronger the better), and a few paper clips. Here’s what you do:

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1. Take a nail in one hand and the magnet in the other.

2. Stroke the magnet along the nail. Make sure to always stroke in the same direction. From the head to the tip for example. Do that at least twenty times.

3. Now see if your nail can pick up any paper clips. Feel free to strengthen your magnet nail by continuing to stroke the nail with the permanent magnet.

You actually twisted and turned atoms! As you moved the permanent magnet over the nail the iron atoms in the nail actually turned, to align themselves with the magnetic field of the magnet. Once enough iron atoms turned the nail itself became a magnet!

Now let’s destroy the magnetized nail… and turn it back into a regular old nail. Here’s what you do:

1. Drop it on a hard surface. A table, floor or sidewalk would work well.

2. Drop it again.

3. Drop it again.

4. Drop it….you get the picture. Drop it four or five times.

5. Now see if it picks up any paper clips. Is the nail still a magnet?

Here you took atoms that were all nicely lined up and messed them up so they pointed in different directions. Since they weren’t lined up as nicely anymore they had much less or perhaps no magnetic force. If you remember the magnets in a box that we were talking about before. This is like you took that box that had all the magnets lined up and dropped it. CRASH! They get all jumbled up and next thing you know the box no longer has nearly as strong of a magnetic force.

Magnets Are Picky Where They Are Sticky

“So, how come I can get a magnet to stick to a refrigerator but not my brother’s head?” Ah, I’m glad to see that you’re experimenting! (You might not want to use your siblings as test subjects though…just a thought.) In a way, you could say that magnets only stick to other magnets. I know you refrigerator is not a magnet but bear with me for a second. Your fridge is made of a metal that has iron in it.

Remember that each iron atom is kind of like a little magnet. So your fridge is made of bunches of little magnets. The reason you can’t stick paper clips to your fridge is that all those little “atom magnets” are pointing in different directions and canceling out their magnetic fields. But what happens when a magnetic field gets close to those little “atom magnets”? They turn. The atoms turn so that their poles are opposite of the poles of the magnet. (We’ll talk more about poles in a later lesson.)

Since they have turned, they now act like a magnet and the fridge magnet can now be attracted to the atoms in the fridge. Once you remove the fridge magnet, the atoms in that part of the fridge go back to being mixed up. Here’s what you do:

1. Attach a paper clip to your magnet.

2. Can you dangle another paper clip from the end of your first one?

3. How many can you dangle from each other. Two, three, four, more?

4. What happens if you remove the permanent magnet from the top of the chain?

The paper clips became temporary magnets didn’t they? The permanent magnet turned the iron atoms in the paperclips so that they aligned with the field of the permanent magnet. Since those atoms are all facing in a similar direction, they can now create a magnetic field of their own. So the paper clip becomes a magnet as long as a magnet is near it. Once the permanent magnet gets too far away, the atoms go back to mish-mosh and no longer have much of a magnetic field.

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Magnetic Grape

Sunday April 4, 2010

Every atom has electrons, and electrons both go around the core and also spin. Depending on how they spin and how much energy the atom has will determine what kind of magnetic properties your atom will have.

Iron is ferromagnetic, which means it’s attracted to both poles of a magnet – bring a nail close to any part of a magnet and you’ll always feel a pull, never a push.

Water (which is what your grape is mostly made up of) is diamagnetic. Things that are diamagnetic are repelled by both poles of a magnet, although very weakly (almost a million times weaker than ferromagnetic).

Paramagnetic materials (like a soda can, hydrogen, lithium, and liquid oxygen) is very weakly attracted to both magnetic poles, but it’s not noticeable until you bring the temperature of the soda can WAY down.

Here’s a nifty way to see diamagnetic properties in a material. Ready?

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Materials:

grapes
straw
string or fishing line
strongest magnet you own
tape
chair or table

Diamagnetic

Diamagnetic materials (like bismuth, water, and graphite) have very weak magnetic fields. When the electrons have about the same number spinning left and spinning right, they each other out and the atom has no magnetic poles. However, if you bring a magnet near, the magnetic field causes the individual electrons in the atom to move, and since moving electrons create a magnetic fields, the electrons create a magnetic field opposite to the original magnetic field and the atom moves away from the magnet. The effect is very weak, but with enough care you can see this effect in water (which is what a grape is mostly made up of).

Paramagnetic

Paramagnetic materials (like aluminum, helium, and platinum) need to be chilled in order for their magnetic fields to be noticeable. Here’s why: what if the atom has more electrons spinning left than right? When this happens, the atom now has magnetic poles (north and south), and you can think of each atom like a little magnet.

However, these magnets are not all lined up in the same direction, so their overall magnetic effect cancels out. If you bring in a magnet (or place the atoms in a magnetic field), they start to line up in the same direction and the material starts to become magnetized. But not quickly, or easily, because the atoms still have so much energy that they keep bouncing around, even when in a solid state.

So to magnetize something quickly, you need to bring down the temperature to reduce the motion of the atoms start to really line up. Paramagnetic materials are attracted to both ends of a magnet.

Ferromagnetic

There are four elements (iron, nickel, cobalt, and gadolinium) that most permanent magnets are made up of. These atoms stay lined up together, even when they are at a temperatures that would cause other atoms to bounce out of alignment. The magnetic effects are mostly caused by the innermost electrons which all aligned the same way, and contribute the magnetic field.

Antiferromagnetic

Some paramagnetic materials (like chromium and manganese) have atoms pair up and cancel each other out. The north pole of one atom will line up with the south pole of another.

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Curie Heat Engine

Sunday April 4, 2010

marie-curie — Marie Curie, a scientist famous for being the first person to receive two Nobel Prizes as well as her extensive work on radioactivity.

Magnetic material loses its ability to stick to a magnet when heated to a certain temperature called the Curie temperature. The Curie temperature for nickel is 380^oF, iron is 1,420^oF, cobalt is 2,070^oF, and for ceramic ferrite magnets, it starts at 860^oF.

We’re going to heat a magnet so that it loses temporarily loses its magnetic poles, and watch what happens as it cycles through cooling. Pierre and Marie Curie’s first scientific works were actually in magnetism, not chemistry, and their papers in magnetic fields and temperature when among the first noticed by the scientists at the time.

Are you ready to see what they figured out?

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Materials:

large ceramic magnet
tiny bead magnet
copper wire
pen
candle (with adult help)
framework to hold the setup (watch video first)

Download Student Worksheet & Exercises

The Curie temperature for the ceramic magnet is much higher than a candle can produce, which is why the permanent magnet isn’t affected by the flame. The Curie temperature for the tiny bead magnet is around 600^oF, which is easily obtainable by your candle.

At the end of the swinging wire, there’s a tiny bead magnet, which is quite strong for its size. The magnet is attracted to the large ceramic magnet and moves toward it, almost touching it. The candle heats up the tiny bead magnet, causing it to temporarily lose its magnetism by adding energy into the atom and randomizing their orientation within the magnet. You’ll notice that the magnet quickly regains its magnetism after it cools. While you can permanently destroy the magnetic field in the bead magnet, you’d need something hotter than a propane torch to do it.

By the way, the Curie temperature for ceramic rare earth magnets is just under 600^oF, also within reach of your candle’s heat. The magnets are also on the small size, so they tend to heat up faster.

Exercises

Why does the tiny magnet lose its attraction to the large magnet?
How long does it take for the attraction-repulsion cycle to repeat?
Draw out your experiment, explaining how it works and labeling each part:

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Linear Accelerator

Sunday April 4, 2010

There are two ways to create a magnetic field. First, you can wrap wire around a nail and attach the ends of the wire to a battery to make an electromagnet. When you connect the battery to the wires, current begins to flow, creating a magnetic field. However, the magnets that stick to your fridge are neither moving nor plugged into the electrical outlet – which leads to the second way to make a magnetic field: by rubbing a nail with a magnet to line up the electron spin. You can essential “choreograph” the way an electron spins around the atom to increase the magnetic field of the material. This project is for advanced students.

There are several different types of magnets. Permanent magnets are materials that stay magnetized, no matter what you do to it… even if you whack it on the floor (which you can do with a magnetized nail to demagnetize it). You can temporarily magnetize certain materials, such as iron, nickel, and cobalt. And an electromagnet is basically a magnet that you can switch on and off and reverse the north and south poles.

The strength of a magnetic field is measured in “Gauss”. The Earth’s magnetic field measures 0.5 Gauss. Typical refrigerator magnets are 50 Gauss. Neodymium magnets (like the ones we’re going to use in this project) measure at 2,000 Gauss. The largest magnetic fields have been found around distant magnetars (neutron stars with extremely powerful magnetic fields), measuring at 10,000,000,000,000,000 Gauss. (A neutron star is what’s left over from certain types of supernovae, and typically the size of Manhattan.)

Linear accelerators (also known as a linac) use different methods to move particles to very high speeds. One way is through induction, which is basically a pulsed electromagnet. We’re going to use a slow input speed and super-strong magnets and multiply the effect to generate a high-speed ball bearing to shoot across the floor.

For this experiment, you will need:
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• Wood or plastic ruler with a groove down the center
• Thick rubber bands or strong, super-sticky tape
• Four super-strong magnets (try 12mm or ½” neodymium magnets)
• Nine steel ball bearings (1/2”, 5/8”, or other sizes)

Here’s what you do:

Download Student Worksheet & Exercises

Question: Does it really matter where where you start the first ball bearing? If so, does it matter much?

What’s going on? The metal ball bearing is seriously attracted to your magnets, and this pull intensifies the closer the ball gets to the magnet (inverse-square law). When the ball smacks into the magnet, the energy wave from the impact zips through the magnet and attached ball bearings until it knocks the furthest ball free, which has the least magnetic pull on it (it’s furthest from the magnet)… which is good, or it would be slowed down and possible reattached to the magnet it just broke away from.

With each impact, there’s an increase in velocity. Imagine if you had a hundred of these things lined up… how fast could you get that last ball bearing going?

After each firing, you have to reset your system, and chances are, it takes a bit of effort to pull the ball bearings from the magnets! you are providing the energy that gets released during each collision and adds to the velocity of the ball bearings.

Want to turn this into a Science Fair Project? Click here for step-by-step instructions.

Exercises

Does it really matter where you start the first ball bearing? If so, does it matter much?
Why does only the last ball go flying away? Why don’t the others break away as well?
What happens if you try this experiment without the magnets?
How many inches did the first initial ball (the one you let go of) travel?
How many inches did the last ball (the one that detached from the magnet) travel?
Why did we use four magnets in the second lab? What did that do?

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Unit 11: Magnetism (Magnets) Video

Sunday April 4, 2010

Why do magnets stick together? And why does breaking one in half create a new set of poles? We’re going to explore these and other weird things about magnets. Are you ready? This video will get you started on the right foot for your study into with oddball world of magnets as you detected the earth’s magnetic pulse, discover magnetic levitation, uncover weird eddy currents that counteract gravity, and discover how a grape is magnetic. Let’s get started:

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