Which of these units is used to measure power?

Power is defined as the rate at which work is done or energy is transferred over time. The unit of power is the watt, which is equivalent to one joule per second. This means that if one joule of work is performed in one second, the power exerted is one watt.

Understanding power in terms of electrical systems, for example, a watt indicates how much electricity is used or produced in a circuit. This makes the watt a fundamental unit in both mechanical and electrical contexts, allowing for the measurement of how effectively energy is used over time.

The other units listed serve different purposes: the joule measures energy, the newton measures force, and psi (pounds per square inch) measures pressure. While all these units are important in their respective fields, only the watt specifically quantifies power.