What happens when a magnet is cut in two? Does the strength of an electromagnet depend on the number of turns of wire? If you have two magnets how can you find out which one is stronger?
A couple of different things can happen when you cut a magnet in half.If you do it gently you can end up with two magnets. You can think of a magnet as a bundle of tiny magnets, called magnetic domains, that are jammed together. Each one reinforces the magnetic fields of the others. Each one has a tiny north and south pole. If you cut one in half, the newly cut faces will become the new north or south poles of the smaller pieces. You could keep slicing smaller and smaller slices like a loaf of bread and keep getting thinner magnets, each with a new set of poles. Remember, I did say though you only get two magnets if you cut them gently. The magnetic domains in a magnetic material can be knocked loose, by bumping or vibrating the magnet (like when sawing it in half). If knocked loose, the domains are no longer arranged neatly, so they do not reinforce each other. If they are in a random orientation, with their fields pointing all over the place, they cancel each other out.
The number of turns of wire does determine the strength of an electromagnet. There is a simple experiment to prove that to yourself. Wrap iron nails with different amounts of thin, insulated wire, and connect them, one at a time to a small battery. There are several ways to measure the strength of these different electromagnets. There are meters called gauss meters. You just place the gauss meter probe in the magnetic field and it will tell you the strength of the field at that point. The meters cost around $1,000. I'm almost sure that is more than you can afford with your allowance. A reasonable method to measure magnet strength is to simply count how many of a small item that each magnet will pick up. Steel paper clips are a good choice. It won't give you an absolute measure of a magnet's strength, but it is a reasonable way to compare two similar magnets. They have to be similar magnets because you are comparing two things at the same time with this sort of test, the strength of the field and the size of the field. A magnet with a larger, but weaker field, might still pick up more weight than one with a very strong field over a very small area.
Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)