Electromagnetism

If you’ve never played with magnets then you should!

If you have, you’ll know that magnets can attract some types of metal, and the strength of the attraction increases as the magnet and the metal get closer together. We say that there’s a force acting between the magnet and the metal.

If you are reading this you are using electricity. It turns out that electricity and magnetism are two symptoms of a single underlying thing. There is a force which acts between protons and electrons, which we call electromagnetism. This force is attractive been a proton and an electron, but repulsive between electrons or between protons. When we talk about an electric current flowing in a circuit, we actually mean that electrons are being forced to move around the circuit by an electromagnetic force. Crudely you can think of a battery as a container in which protons and electrons start evenly spread out. When you charge the battery, the charger applies an electromagnetic force that makes the electrons pile-up in one part of the battery, leaving too few electrons in the other part. When you then use the battery, all the electrons that have been piled up rush back (via your phone, or torch, or car starter motor, or whatever) to the other part of the battery. When there’s no longer any build-up of electrons the battery is flat.

If you want a nice analogy to understand batteries, try this. Imagine a tank half filled with water. The water level is the same throughout the tank. Now imagine you put a divider in the middle of the tank so water can’t flow from one side to the other. Then imagine using a bucket or pump to lift water from one side to the other over the divider. You’ll end up with the tank nearly full on one side and nearly empty on the other. The water on the full side would like to drop down into the empty half of the tank but it can’t because the divider is in the way. Now suppose you connect the two halves of the tank at the bottom with a pipe. The water from the full half of the tank will rush through the pipe to the empty half. Gradually the level on one side of the tank will fall, and the level on the other side will rise until the level is the same throughout, then the water will stop flowing in the pipe. In this analogy the water tank is the battery and the pipe is the electric circuit.