About this blog

Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

Friday, 23 September 2011

Pure Magnetism

Magnets are everywhere, on our fridges, holding bags closed, and even keeping some trains on their rails. But where exactly does this magnetism come from? Is it magical? It certainly seems a bit like it, after all you can’t tell the difference between a magnetic piece of metal and a non-magnetic one just by looking. Well, other than all the magnets you may have seen in your school classes are handily painted red and blue.

Let’s start with that childhood game of getting a balloon, blowing it up and rubbing it on your jumper. Once you’ve charged up the static electricity, you found that it sticks to things like the wall, or your sleeping cat. This is because all that rubbing has created a negative charge on the surface of the balloon, which is then attracted to the positive nucleus of the molecules in the surface you want to attach it to. This charge won’t last forever though, because the system wants to return to its normal state.

And you can make magnets in a remarkable similar way. If you take two metal rods, both of metal containing plenty of iron (called ferrous metals), and use one to stroke the other, you get a weak magnetic effect. What is happening is that you’re starting to align the molecules so that all their dipoles (a fancy way of saying one side is more positive and the other more negative) match up.

This same effect can be achieved much more strongly if you use another magnet to rub the rod with, as the pull on the molecules and the alignment happens much more strongly. This is usually enough to create a permanent magnet.

So what happens if you cut a magnet in half? Do you get a purely positive bit and a purely negative bit? Thanks to the dipoles, this isn’t the case, if you cut a magnet in half, you get two magnets!

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