How a battery works:

http://www.livescience.com/50657-how-batteries-work.html

Make your own batter from a potato:

http://www.wikihow.com/Create-a-Potato-Battery

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