What is a diode?

• A. A semiconductor device with two terminals that typically allows the flow of current in one direction only. It is comprised of a pn junction.
• B. An amplifier that increases signal voltage.
• C. A device that stores energy in a magnetic field.
• D. A microcontroller with programmable logic.

Answer: (A)

A diode is a two-terminal semiconductor device that conducts current primarily in one direction because of a pn junction. When forward-biased, the potential barrier at the junction is reduced, allowing carriers to cross and current to flow; when reverse-biased, the barrier widens and only a small leakage current passes, effectively blocking the flow. This one-way behavior is what makes diodes useful for rectification, clamping, and signal detection. The description matches a diode precisely: a two-terminal device built from a pn junction that conducts mainly in one direction. The other options describe an amplifier, an energy-storage device in a magnetic field (an inductor), and a programmable microcontroller, which are different components.