What is the primary use of a galvanometer in a circuit?

A galvanometer is primarily used to measure current in a circuit. It works by detecting the magnetic field created by an electric current passing through a coil of wire. This magnetic field causes the coil to move, which is indicated by a needle on a scale, allowing for the measurement of the current flowing through the circuit.

The design of a galvanometer makes it particularly sensitive and accurate for detecting small currents, which is essential in many applications, from laboratory experiments to certain types of electrical troubleshooting. When a galvanometer is calibrated properly, it can give direct readings of current, often in milliamperes.

The other options explore different functions that devices in electrical circuits may perform. While voltage and resistance can be measured using other instruments, such as voltmeters and ohmmeters respectively, those devices are not designed to provide the same direct measurement of current that a galvanometer does. Similarly, while switches control the flow of electricity by opening or closing a circuit, they do not measure current. Thus, the primary and most relevant function of a galvanometer is indeed to measure current.