Magnetic Lines?

Open any book or web page that talks about magnets, and you will probably see a drawing that shows magnetic lines of force that extend from one end of the magnet to the other.

Are there really lines of magnetic force as they show in the drawings? Well, lets find out.

To try this, you will need:

- a file
- iron nails
- a small, plastic bottle cap
- clear, dish washing soap
- a strong magnet
- metal paper clips

If you tried the experiment from the Science of Credit Cards video, don't throw away the iron filings. If you did not, then you can use the file and iron nails to make about 1/4 teaspoon of iron filings.

Fill the plastic bottle cap about 3/4 with the dish washing soap.

Soap

Then stir the iron filings into the soap, until they are evenly distributed.

Stir

Place the bottle cap on top of a strong magnet. Watch the iron filings carefully as you put the magnet in place. You should notice that the filings are attracted to the magnet.

Lines wide

Looking closer, the magnetic filings stick together, forming lines that look very much like the drawing in the book. So there really are lines of magnetic force, right? No.

Wait a minute! What do you mean by "No"? I can see the lines, right there in front of me!

Well, there are lines of iron filings, but there are no lines of magnetic force. The magnetic field that extends around the magnet does connect one end to the other, but it is spread evenly, not in specific lines of force. Then why do the filings line up like that? To find out, lets look at some paper clips.

Pour a pile of paper clips on the table, and put the magnet into the pile. When you lift the magnet, the paper clips stick together, forming magnetic chains.

Paperclips

Each of the paper clips in the chain now has a north and south magnetic pole. In the photo, the paper clips are sticking to the north pole of the magnet, so on the first paper clip, the end that is touching the magnet will be a south magnetic pole. The other end will become a north magnetic pole, attracting the next paper clip in the chain. That paper clip will also develop north and south magnetic poles, and will attract the next paper clip in the chain.

field lines

The same thing happens to the iron filings. They attract each other, end to end, to form chains, just as the paper clips did. That is what forms the lines you see, not invisible lines of magnetic force. How do we know?

Remove the magnet, and stir the soap again. Put the magnet back, and you will see the lines form again, but if you look closely, you will notice that they are not in exactly the same place. If there really were actual lines of force, the filings would line up in the same place each time. Since the magnetic field surrounds the magnet evenly, instead of in lines, the locations of the chains of iron filings are random each time. You always get the chains, but they are always in different places.

The lines in the drawings work well for explaining magnetic fields, and the chains of iron filings reinforce that idea, but when you observe carefully, there are no magnetic lines of force.

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