What happens to a fuse when there is excess current?

When excess current flows through a fuse, it causes the fuse element to melt. Fuses are designed to protect electrical circuits by breaking the circuit when the current exceeds a certain level. The fuse contains a metal wire or strip that has a specific melting point. When the current exceeds this threshold, the heat generated by the current flow raises the temperature of the fuse element to the point where it melts, effectively interrupting the flow of electricity and preventing potential damage to the circuit components or reduction of safety hazards.

This melting process is essential for the functionality of a fuse, as it ensures that the circuit is protected from overcurrent conditions. The other options do not accurately describe the primary mechanism of a fuse’s operation. For example, expansion might occur due to heat but is not the primary action that a fuse takes in response to excess current. Glowing may happen as the fuse heats up, but this is not the defining action that protects the circuit. Adding resistance is not a characteristic of how a fuse functions; instead, it is a simple device designed to fail when necessary, rather than alter its resistance dynamically.