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In 1948, the invention of the transistor at Bell Telephone Laboratories, led to a revolution in electronics. Modern transistors are made of silicon. After oxygen, silicon is the most common element on this planet. It is neither a good conductor or insulator. It is a semiconductor.
Transistors are semiconductor devices with three leads. A very small current at one lead can control a much larger current flowing through the other two leads. This means that transistors can be used as amplifiers and switches. The two main families are bipolar and field-effect transistors (fets). Many different kinds of transistors are available for various purposes. The small switching transistors are used to amplify low level signals. Power transistors are used in high power amplifiers. High-frequency transistors operate at radio, television and microwave frequencies.