Watts measure what?

• A. The rate of energy usage
• B. Electrical resistance
• C. Electrical energy per second
• D. Electrical voltage

Answer: (C)

Power in an electrical context is the amount of energy transferred per unit time. Watts are the units that express this rate, and by definition one watt equals one joule per second. So watts measure electrical energy per second. You can also think of power as the rate at which energy is used, but the exact unit-based description is energy per second. The other quantities refer to resistance and voltage, not power.