Which safety device melts a thin metal strip when there is excessive current?

• A. Capacitor
• B. Diode
• C. Fuse
• D. Breaker

Answer: (C)

A fuse protects circuits by melting a thin metal link when current becomes excessive. The link is designed to heat up quickly because the power dissipated in the metal grows with the square of the current (I^2R). When the current exceeds the fuse rating, enough heat is produced to melt the strip, opening the circuit and stopping current flow to prevent damage or fire. This intentional, fast open-circuit failure is exactly what a fuse is for.

Capacitors store electrical energy rather than interrupting current; diodes control the direction of current flow rather than protect against overcurrent; and a circuit breaker trips a switch to interrupt the circuit—often via a thermal or magnetic mechanism—rather than melting a thin metal strip.