I wanted to do an experiment about demagnetizing magnets, and the simplest way was to begin by magnetizing some paperclips. Once we do that, then we will explore ways to get rid of the magnetism.
To make a magnet, you will need:
- a strong, permanent magnet
- several paper clips
- steel wool
- a sheet of paper
One of the easiest ways to make a magnet is with another magnet. Straighten out the paper clips.
Hold a straightened paper clip by one end. Hold the magnet in your other hand Bring one end of the magnet to the paper clip at the point where you are holding it and then slide the magnet away from you, along the paperclip. Move the magnet away from the paper clip when you reach the end, and repeat the process several times. Be sure that you only move the magnet along the paper clip in one direction, away from your hand.
After doing that several times, put away your permanent magnet and get out the paper and the steel wool. You put away the permanent magnet because if the tiny bits of steel wool get stuck to it, they are almost impossible to get off. If you want to use your permanent magnet to play with the steel wool, put it in a plastic bag first. That will keep the bits separated from the magnet.
Place the sheet of paper on a flat surface and hold the steel wool over it. Rub two pieces of steel wool together and you will see lots of tiny bits falling on the paper. Bring the end of one of your non-magnetized paperclips near the steel wool. The bits probably won't react. Then bring the end of your magnetized paper clip near the steel wool. This time you will see it stick to the paper clip. Your paper clip is now a magnet.
What happened to magnetize it? Inside a piece of iron or steel are tiny groups of atoms called domains. Each of these domains is a tiny magnet, with a north and south pole. In unmagnetized iron, they domains are arranged randomly with their north and south poles pointing in different directions. The magnetic fields cancel each other out, and so the entire piece is not a magnet. When you move the magnet along the steel of the paper clip, the magnet pulls on each domain and shifts the north and south pole, so that most of them wind up pointing in the same direction. That magnetizes the paperclip. The more domains you get lined up, the stronger the magnet will be.
While you are playing with your magnet, check to see which parts of your magnet have the strongest magnetic field. You can also notice how much of the steel wool the magnet will pick up when it is straight and then bend it into a horseshoe shape, where the two ends are near each other and try again. Does a horseshoe magnet pick up more than a straight, bar magnet?
Now that you have made a magnet, we will try to demagnetize it. Can you think of something to try?
Think about it, and when you think you know the answer, then continue.
What about reversing the process? If you rub the magnet in the opposite direction, will it undo what you did? Try it and see. If it demagnetizes the paperclip, remagnetize it again.
What if you try using the other end of the magnet to move along the paperclip? Try it and see. Once again, remagnetize the paperclip, if necessary.
What if you broke the magnet in half? Lets try that too. Hold one end of the paperclip in each hand and bend it back and forth a couple of times. This should cause the magnet to break in half. Test each half with the steel wool. This time, you probably should magnetize a new paperclip.
What if instead of breaking it, you just beat it up a bit? Hold one end of the paperclip and whack the other end on the table a few times. Does that have an impact on how magnetic it is?
What happened? Moving the magnet the opposite direction or using the other end of the magnet will lessen the magnetism with each stroke, until it is mostly demagnetized. If you continue past this point, you will remagnetize the paperclip with the opposite alignment. The end of the paperclip that was the north pole will now be the south pole. Continued stroking will make the magnet stronger, just as it did the first time you magnetized it.
Breaking the magnet does not demagnetize it. Instead, each half will be a complete magnet, each with a north and south pole. Inside the paperclip, the domains are still lined up.
Banging the paperclip on the table will demagnetize it. Each time you hit the paperclip on the table, you move some of the domains out of line. This is why it is important not to drop or bang your permanent magnet. Each time you do, it becomes a little weaker.