Physics of the Radio Without a Battery — the Crystal Radio

Photo: Rhett Allain. A coil of wire is a key part of a crystal radio

It’s also called a foxhole radio. The idea is that you can build a radio from some pretty basic parts and then use this to listen to nearby radio stations. It doesn’t even need a battery. If you have been watching Masters of the Air (on Apple TV), you can see one of these radios in episode 7 (that’s all I’m going to say about the show to avoid spoilers).