(n.) 1. The rate at which electrical energy is converted to another form. In a direct current (DC) circuit, it is the product of applied voltage and current. It may also be calculated by the voltage squared divided by the resistance, or the current squared times the resistance. In an alternating-current (AC) circuit, it is the product of the effective values of the voltage and current with the cosine of the phase angle (between current and voltage). See apparent power and rms power. 2. In physics, this is the rate at which work is done, expressed as the amount of work per unit time. A common unit of measurement is the watt, defined as 1 joule per second, which is equal to the power dissipated by 1 ohm of resistance when power 1 ampere of current passes through it. One unit of horsepower is equal to 745.7 watts.