How a battery works:
Make your own batter from a potato:
Make your own magnetic train with batteries, magnets, and copper wire!
http://frugalfun4boys.com/2015/03/10/how-to-build-a-simple-electromagnetic-train/
History of Electromagnetism (includes explanation of magnetic train):
https://skullsinthestars.com/2014/12/12/the-mystery-of-the-magnetic-train/
How a theremin works:
http://electronics.howstuffworks.com/gadgets/audio-music/theremin.htm