Which instrument measures current and must be connected in series?

Which instrument measures current and must be connected in series?

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

Answer: (D)

Measuring current requires you to place the instrument in series with the circuit so that the same current flows through the meter and the load. An ammeter is designed with very low internal resistance to minimize voltage drop, and its insertion in series ensures it reads the true current in the branch. If it were placed in parallel, most of the current would bypass the meter or create a short, giving an incorrect reading or damaging the circuit. By contrast, a voltmeter is connected in parallel to measure voltage across a component; an ohmmeter is used with the circuit de-energized and connected across the component to measure resistance; a wattmeter measures power and typically combines voltage and current inputs in a specific configuration, not simply a series current measurement. Therefore, the instrument that measures current and must be connected in series is the ammeter.

Measuring current requires you to place the instrument in series with the circuit so that the same current flows through the meter and the load. An ammeter is designed with very low internal resistance to minimize voltage drop, and its insertion in series ensures it reads the true current in the branch. If it were placed in parallel, most of the current would bypass the meter or create a short, giving an incorrect reading or damaging the circuit. By contrast, a voltmeter is connected in parallel to measure voltage across a component; an ohmmeter is used with the circuit de-energized and connected across the component to measure resistance; a wattmeter measures power and typically combines voltage and current inputs in a specific configuration, not simply a series current measurement. Therefore, the instrument that measures current and must be connected in series is the ammeter.