[glatt]

Originally Posted by Catwoman

How?? How is the signal saved in magnetic dust? Do you just get a pile of crushed magnets and sing into them?

It gets complicated, and my explanations are an over-simplification, but here goes:

If you understand how a speaker works, a microphone works basically the same way, but in reverse.

Sound waves from your voice hit a paper cone or membrane which is attached to a coil of wire. That wire is in a magnetic field. The membrane vibrates when your voice's sound waves hit it, and so does the wire coil. When the wire coil moves through the magnetic field, a current is created. I don't know why a current is created when a wire is moved through a magnetic field, it just does. That's how generators work, incidentally. The coil vibrates in a certain way, and the resulting current has a pattern to it. A signal. That signal goes through bunch of circuitry, but basically it goes to the recording "head" on the tape recorder. The recording head is like an electromagnet.

An electromagnet is a loop of wires that has electricity passing through it which causes a magnetic field. They use huge versions of these things in junkyards to pick up cars with cranes and move them around and drop them. Anyway, the recording head, which is basically an electromagnet, pulses a magnetic field that varies in intensity with the strength of the electric signal that comes from the microphone. This pulsing field rearranges the magnetic dust on the tape as the tape slowly travels by. You end up with a tape that has a pattern of strong magnetism and weak magnetism in different areas.

When you want to play the tape back, another head which is basically also just an electromagnet will read it. This electromagnet is turned off so that it can pick up the signal. The magnetic signal on the tape goes past the "coil" of wires that is the playback head, it is a mganet that moves in relation to the coil, and it creates a signal. That signal goes to the amplifyer and then to the speakers.

As you can see, there are two basic principles at play here. The idea that you can create electricity by passing a looped wire through a magnetic field and it's inverse, that you can create a magnetic field by passing electricity through a looped wire. Most of what we do with electricity in this world comes from these principles.

I'm just typing this stuff off the top of my head, so I hope it makes sense. There are probably better places to go that will explain this. LikeHow stuff works

Edit: I type too slow.
Edit again: You can stand on sm. He knows more about this than I do, I didn't know the playback head had electricity passing through it. I thought it was probably totally passive.