Which instrument can be used to measure the frequency of an AC supply?

A frequency counter is specifically designed to measure the frequency of alternating current (AC) supplies. It works by counting the number of cycles in a given time period, allowing it to accurately determine the frequency in hertz (Hz). This instrument is essential in various applications, including telecommunications, audio engineering, and electronics, where knowing the precise frequency of the AC supply is critical for performance and compatibility with other equipment.

In contrast, a voltmeter measures the voltage level in an AC circuit but does not provide any information about frequency. An ampermeter, on the other hand, measures the current flowing through a circuit and is similarly unaware of frequency. A power meter measures the actual power consumed by an electrical load, which again does not provide direct information on frequency. Thus, the frequency counter is the correct choice when it comes to measuring the frequency of an AC supply.