Rub a balloon on your hair and it crackles. Stick a fridge magnet to the door and it clings. For centuries people thought electricity and magnetism were two completely separate mysteries. Then came one of the greatest surprises in all of science: they are secretly the same thing.

Here is the deep link in two lines. Push electricity — a current — through a wire and it makes an invisible magnetic field around it. And run it the other way: move a magnet near a wire, so the field changes, and it pushes a current back through the wire. Electricity makes magnetism; changing magnetism makes electricity. That single two-way partnership runs almost every machine you own.

Every magnet is wrapped in a magnetic field — invisible lines that loop out of the north pole and curve round into the south. You can't see them, but iron filings line up along them. Slide the strength up: a stronger magnet reaches further, and its arrows push out wider. Nothing is touching, yet the field is real.

Your journey through electromagnetism

Start by learning to see the invisible in . Then build your own magnet out of a coil and a battery in . Discover how a magnet can push a wire — the trick behind every electric motor — in . Finally run the whole idea backwards to generate electricity from a moving magnet in .

First met a magnet over in ? This strand picks up where that left off and reveals what the field is really doing.