TRANSISTOR

TRANSISTOR

 -is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. (wikipedia)

2 Main types of types of Transistor:

1. BJT- Bipolar Junction Transistors 
2. FET - Field Effect Transistors

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A Photo below is a 2N3904 NPN bipolar junction transistor which can be used for a low-power amplifier or for switching applications. Read more HERE