A diode conducts current when it is in which bias condition?

• A. Reverse bias
• B. Forward bias
• C. No bias
• D. Positive bias

Answer: (B)

Diodes conduct when forward biased, meaning the anode is more positive than the cathode. This lowers the energy barrier of the p–n junction, narrows the depletion region, and allows charge carriers to cross, so current flows. As you increase the forward voltage, the current rises quickly, with a typical turn-on around about 0.7 V for silicon diodes (lower for germanium). If the diode is reverse biased, the depletion region widens and current is blocked, aside from a tiny leakage. With no external bias, there’s no driving force, so the diode is effectively off. Positive bias describes the same forward-biased condition in common terminology, so it also leads to conduction.