One family of transistors is known as bipolar transistor(bipolar junction transistors BJTs) of which there are two basic types called NPN and PNP. These names relate to the way in which the silicon is doped .
A bipolar transistor is comprised of base, emitter, and collector and is a current-controlled
device with a low input impedance.
The first transistor was invented at Bell Laboratories in 1947 by Nobel-Prize physicists John Bardeen, William Shockley, and Walter Wratain.
Resistors, capacitors and inductors are known as passive components . Electronic components which produces changes in circuit conditions by reacting to applied signals are known as active components . The majority of active components used in electronic circuits use semiconductors .
A semiconductor can sometimes act like a conductor, and at other times like an insulator in the same circuit.
The term semiconductors arises from the ability of these materials to conduct “part