I have heard transistors are used in many electronic devices to amplify current such as in microphones which amplify the sound. I want to know how do they what do they do? How can a transistor just amplify electric current from nothing?
marked as duplicate by Leon Heller, stevenvh, Kellenjb, Kortuk♦ Jan 28 '12 at 17:53
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Transistor needs a power source, it can't amplify a signal "from nothing".
You ask the very basics. I think you should read the first chapter of some book. For example Principles of Transistor Circuits.
Or at least Wikipedia article on transistor.