Which instrument measures electrical power?

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

Answer: (A)

Power is found from multiplying voltage by current, P = V × I. A direct measurement of electrical power is done with a wattmeter. The instruments listed measure other things: a voltmeter reads voltage, an ammeter reads current, an ohmmeter reads resistance, and a thermometer reads temperature. Because none of these alone gives power, you wouldn’t get a direct power value from any single one of them. In practice, you could estimate power by multiplying the measured voltage and current, or use a dedicated wattmeter for an actual reading, especially in AC circuits where you’d also account for power factor.