A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because <answer>the controlled (output) power can be higher than the controlling (input) power</answer>, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
Why does a transistor increase a signal?
the controlled (output) power can be higher than the controlling (input) power