What is the basic function of a diode?

• A. Allows current to flow in one direction only
• B. Stores energy
• C. Blocks current in both directions
• D. Amplifies current

Answer: (A)

Diodes act as one-way valves for electric current. A diode has a p-n junction, and when it’s forward biased the electric field at the junction is reduced, allowing charge carriers to cross and current to flow in that direction with relatively low resistance. When the polarity is reversed, the depletion region widens and the barrier becomes larger, blocking current except for a tiny leakage current. So the core function is to conduct current in one direction while preventing it in the opposite direction. This is why diodes are used in rectifiers to convert alternating current to direct current and to protect circuits from reverse polarity. They don’t store energy like a capacitor, they don’t block current in both directions, and they don’t amplify current.