The correct answer is: C. both voltage and current.
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.
Transistors were first developed in Germany in the early 1940s, but they did not become commercially available until the late 1940s. The first transistors were made of germanium, but they were soon replaced by silicon transistors, which are more stable and reliable. Transistors have revolutionized the electronics industry, and they are now used in virtually all electronic devices.
Transistors can be classified into two main types: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs are made of three semiconductor regions: the emitter, base, and collector. The emitter and collector are heavily doped with impurities, while the base is lightly doped. When a small voltage is applied to the base-emitter junction, a large current can flow through the collector-emitter junction. This is how a BJT amplifies a signal.
FETs are made of two semiconductor regions: the source and drain. The gate is a third region that is insulated from the source and drain by a thin layer of oxide. When a voltage is applied to the gate, it creates an electric field that attracts or repels electrons in the channel between the source and drain. This changes the resistance of the channel, and it controls the current that flows through the device.
Transistors are used in a wide variety of electronic devices, including computers, cell phones, and televisions. They are also used in power amplifiers, radio transmitters, and other industrial applications.