The correct answer is B. A transistor has two doped regions.
A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The three terminals of a transistor are called the emitter, base, and collector. The emitter and collector are connected to the external circuit, and the base is connected to the control signal. When a small voltage is applied to the base, it causes a much larger current to flow between the emitter and collector. This is how a transistor amplifies a signal.
The two doped regions in a transistor are the emitter and collector. The emitter is doped with a higher concentration of impurities than the collector. This difference in doping concentration creates a voltage difference between the two regions. When a small voltage is applied to the base, it causes electrons to flow from the emitter to the collector. This flow of electrons is the amplified signal.
The answer to the question “A transistor has how many doped regions?” is B. A transistor has two doped regions, the emitter and the collector.