What is the function of a relay in an electrical circuit?

The function of a relay in an electrical circuit is primarily to switch circuits open or closed. A relay is an electromagnetic switch that utilizes an electric current to open or close another circuit. It can control a larger amount of current by using a smaller control signal. When the relay coil is energized, it generates a magnetic field that moves a lever or armature, thus making or breaking the connection in the circuit it controls.

Relays are essential in automation and control systems, enabling one circuit to control the operation of another while providing electrical isolation between the two. This feature is crucial in many applications, from simple light switches to complex industrial control systems.

The other options do not align with the primary purpose of a relay. For instance, measuring electrical voltage is typically done with a voltmeter, converting AC power to DC power is the role of rectifiers, and charging a battery involves chargers specifically designed for that function. Therefore, the role of a relay is distinctly focused on switching circuits, making option B the appropriate answer.