A watt-hour meter is used to measure which quantity?

• A. Power
• B. Energy
• C. Total Power
• D. Energy per hour

Answer: (B)

A watt-hour meter measures energy used over time. It keeps a running total of the electrical work done by the load by integrating the instantaneous power (how much power is being drawn at each moment) as time passes. The result is energy, typically stored in units like watt-hours or kilowatt-hours, which is what utilities bill. This differs from instantaneous power, which a wattmeter would read at a single moment, and it isn’t a separate quantity like “energy per hour”—that would imply a rate (power), not accumulated energy. For example, a 100 W load running for 2 hours uses 200 watt-hours of energy.