Which description matches a fuse?

• A. A device that allows current to flow in one direction
• B. A device that blocks current when cold
• C. A device that stores electrical energy
• D. A safety device consisting of a strip of wire that melts and breaks an electric circuit

Answer: (D)

Fuses protect circuits by interrupting current when it gets too high. They use a thin strip of metal that heats up as current flows; if the current exceeds the fuse’s rating, the strip melts and the circuit opens, stopping all current. Because it’s a sacrificial safety component placed in series, once it blows it must be replaced to restore protection. That exact description—a safety device consisting of a strip of wire that melts and breaks an electric circuit—captures how a fuse works. Other choices point to different components: a device that allows current in one direction is a diode; a device that blocks current when cold describes a temperature-sensitive resistor that changes resistance with temperature; and a device that stores electrical energy is a capacitor.