What is the main purpose of a circuit breaker?

The main purpose of a circuit breaker is to protect electrical circuits by interrupting the flow of current during an overload or a short circuit. When excessive current flows through the circuit, the circuit breaker automatically opens the circuit, stopping the current flow and preventing potential damage to the wiring, connected devices, or even reducing the risk of fire. This automatic interruption is crucial for maintaining safety and ensuring that electrical systems operate within their safe limits.

In contrast, the other options describe functions that are not relevant to the primary role of a circuit breaker. Increasing current flow is contradictory to the intended protective function of a circuit breaker. Measuring voltage pertains to instruments like voltmeters, which assess electrical potential but do not control current flow. Adding resistance to a circuit involves components like resistors, which influence the current without providing the protective features that circuit breakers offer. Thus, the correct answer highlights the protective mechanism that is fundamental to the operation of a circuit breaker.