Which instrument measures current in an electrical circuit?

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

Answer: (C)

Measuring current requires an instrument that is placed in series so the same current flows through it. The ammeter is designed for this purpose and has very low internal resistance, so inserting it into a circuit doesn’t significantly alter the current. When connected correctly, it reads the current in amperes.

Voltmeter, by contrast, measures voltage and is connected in parallel to a component. Ohmmeters measure resistance by applying a small current and measuring the resulting voltage, and are typically used on components when they’re not powered. Wattmeters measure power by multiplying voltage and current, and are used to track real power in a circuit.