Resistor Actual Power (for Voltage difference)


Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.

Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes by the electric power industry through an electric power grid. Electric power is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer.

Electrical power provides a low entropy form of energy and can be carried long distances and converted into other forms of energy such as motion, light or heat with high energy efficiency.

In the case of resistive (Ohmic, or linear) loads, Joule’s law can be combined with Ohm’s law (V = I·R) to produce alternative expressions for the amount of power that is dissipated.

The formula shown here calculates the actual electric power on a resistor when the actual applied voltage differs from the rated voltage (e.g. 115V instead of 230V)

Related formulas


PAactual power (watt)
PRrated power (watt)
VAactual voltage (V)
VRrated voltage (V)