What does a diode do?

• A. A diode stores energy
• B. A diode allows current to flow in only one direction
• C. A diode amplifies current
• D. A diode reduces resistance

Answer: (B)

A diode acts as a one-way valve for electricity. When the anode is more positive than the cathode (forward bias), the barrier at the PN junction is lowered and current can flow. When the polarity reverses (reverse bias), the barrier widens and only a tiny leakage current passes, so the current is effectively blocked. This directionality is why a diode is used to convert alternating current to direct current and to protect circuits from reverse polarity. A diode doesn’t store energy like a capacitor, nor does it amplify signals like a transistor, and its job isn’t to reduce resistance but to enforce current flow in a single direction.