Ans:A Transistor is an semiconductor,A transistor controls a large electrical output signal with changes to a small input signal.Since a large amount of current can be controlled by a small amount of current, a transistor acts as an amplifier.A transistor acts as a switch which can open and close many times per second.The most common type of transistor is a bipolar junction transistor.
Layers with extra electrons are called N-Type, those with electrons missing called P-Type. Therefore the bipolar junction transistors are more commonly known as PNP transistors and NPN transistors respectively.
Bipolar junction transistors are typically made of silicon and so they are very cheap.
