What is the unit of power?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → joule sec−1
Power is the rate of doing work: the work done (or energy used) divided by the time taken. Work is measured in joules and time in seconds, so power is measured in joules per second (J s−1), a unit named the watt (W).
Why the other options are incorrect
Option (1) joule — Incorrect. It is the unit of work and energy, not of the rate at which work is done.
Option (2) joule sec — Incorrect. Energy multiplied by time is the unit of a quantity called action (as in Planck’s constant), not of power.
Option (4) watt sec — Incorrect. A watt for a second is one joule of energy; electricity is billed in a larger unit of the same kind, the kilowatt-hour.