How can a transistor work as an amplifier?
With a field-effect transistor, a small voltage at the input is made to control a current at the output. The current is made to flow through a load, which can be a fairly large resistance. As a result, the output voltage can be many times larger than the input. With the bipolar junction transistor, it is a tiny current at the input that is used to control a much larger current at the output. The ratio of output voltage to input voltage, or output current to input current is a dimensionless value known as gain, or amplification. In tubes, it was called mu, in transistors it is called hFE. If you are interested in learning more, I’d suggest that you go to Radio Shack and get some of their beginner’s books on learning electronics. They have projects you can build, and Radio Shack has all the parts!
