Here's the biggest invention of the 20th century - and the smallest: the transistor, developed in 1947 by John Bardeen and Walter Brattain, and improved by William Shockley. You're probably using a billion transistors right now in your computer. I don't have room to explain how it works in detail, but here's what it does. There's a chip of silicon or germanium made of 2 or 3 la...yers and it has 3 connections called the emitter (E), collector (C), and base (B). Feed a small electric current (red) into the emitter and you get a bigger current (blue) from the collector. That's it! If you feed a quiet sound from a microphone into the emitter, you can use the collector to drive a loudspeaker and get a louder sound; that's how a hearing aid works, and it was the first thing people used transistors for. You can also use transistors to switch things on and off or store numbers - that's how computers use them.
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