A transistor is a semiconductor device used for amplification and switching of electronic signals. It is generally a three terminal device which accepts a small signal on two of its terminals which in turn control a much larger signal on another pair of terminals. The input signal may modulate the output signal in proportion to itself acting as amplifier or may simply start or stop current flow in the output terminals acting as a switch. This ability to control a signal on a different resistance path from a lower resistance path makes it the fundamental component of any electronic system.
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