Which instrument is commonly used to measure current in a circuit?

The ammeter is the instrument specifically designed to measure the current flowing through a circuit. It operates by being connected in series with the load, allowing all the current to pass through it. An ammeter typically provides readings in amperes, which is the standard unit of electrical current.

In contrast, a voltmeter measures voltage, or electrical potential difference, and must be connected in parallel across components in a circuit. This is necessary to get an accurate voltage reading without disrupting the current flow. An ohmmeter, on the other hand, is used to measure resistance in ohms by passing a small known current through a component and measuring the voltage across it. Lastly, a wattmeter measures the electrical power in watts that is being consumed or generated in a circuit, incorporating both voltage and current readings to provide power consumption details.

Therefore, the ammeter is the correct choice when specifically measuring current in a circuit.