What is a transistor?

What is a transistor?

• A. A semiconductor device comprised of an npn or pnp junction with a source, gate, and drain or emitter, base, and collector. A transistor can act as an electrical switch which can turn on and off thousands of times a second. They are used in opamps for signal amplification as well as in digital circuits.
• B. A passive resistor used to limit current
• C. A coil used to store energy
• D. A diode used for rectification

Answer: (A)

Understanding how a transistor controls current and can act as a switch or amplifier is what this item tests. A transistor is a three-terminal semiconductor device, with emitter, base, and collector for a bipolar junction transistor (npn or pnp). A small current or voltage at the base modulates a much larger current flowing from emitter to collector, allowing the device to switch on and off or to amplify signals. This dual capability—control of a large output current by a small input—makes transistors essential in both amplification (as in op-amps) and switching in digital circuits. The other options describe passive or two-terminal components that don’t provide the same current control and amplification behavior. A resistor limits current passively, an inductor stores energy in a magnetic field, and a diode conducts in one direction but doesn’t offer current gain or three-terminal control.

Understanding how a transistor controls current and can act as a switch or amplifier is what this item tests. A transistor is a three-terminal semiconductor device, with emitter, base, and collector for a bipolar junction transistor (npn or pnp). A small current or voltage at the base modulates a much larger current flowing from emitter to collector, allowing the device to switch on and off or to amplify signals. This dual capability—control of a large output current by a small input—makes transistors essential in both amplification (as in op-amps) and switching in digital circuits.

The other options describe passive or two-terminal components that don’t provide the same current control and amplification behavior. A resistor limits current passively, an inductor stores energy in a magnetic field, and a diode conducts in one direction but doesn’t offer current gain or three-terminal control.