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

• A. Voltmeter
• B. Wattmeter
• C. Ohmmeter
• D. Ammeter

Answer: (D)

The instrument used to measure electrical current in a circuit is the ammeter. It must be placed in series with the circuit so that the same current flows through it as through the rest of the components. To avoid significantly altering the current, an ammeter is designed to have very low resistance, so it doesn’t drop much voltage or change the circuit’s behavior. Current is measured in amperes, and the ammeter reads this value.

Voltmeter, by contrast, measures voltage and is connected in parallel across a component to capture the potential difference. Ohmmeter measures resistance and is used when the circuit is de-energized, sending a small current through a component and reading the resulting voltage to compute resistance. Wattmeter measures electrical power and is used in configurations that determine P = VI, incorporating both current and voltage readings.