Which instrument would you place in series with a circuit to measure current?

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

Answer: (C)

Measuring current relies on inserting the instrument directly in the path of the circuit so every ampere flows through it. The ammeter is designed for this purpose and has very low internal resistance, which keeps the voltage drop small and doesn’t appreciably alter the circuit’s current. By placing it in series with the load, you capture the true current flowing through the entire loop. In contrast, a voltmeter is connected in parallel to measure voltage across a component, an ohmmeter is used to measure resistance in a powered-down circuit, and a wattmeter uses both voltage and current to compute power. So the instrument that should be placed in series to measure current is the ammeter.