Electric power

Electric power is the rate of transfer of electrical energy within a circuit. Its SI unit is the watt, the general unit of power, defined as one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively.

In common parlance, electric power is the production and delivery of electrical energy, an essential public utility in much of the world. 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 (as domestic mains electricity) by the electric power industry through an electrical grid.

Electric power can be delivered over long distances by transmission lines and used for applications such as motion, light or heat with high efficiency.

Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter P. The term wattage is used colloquially to mean "electric power in watts". The electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential (voltage) difference of V is: $${\displaystyle {\text{Work done per unit time}}=P={\frac {W}{t}}=V\times I}$$ The voltage between two terminals is defined as the work required to move a unit charge from one terminal to the other against the force of the electric field, so this equation can be derived as

where:

Electric power is transformed to other forms of energy when electric charges move through an electric potential difference (voltage), which occurs in electrical components in electric circuits.

An often confusing aspect of the terminology is that the direction of electric current (conventional current) is defined as the direction that positive charge flows, but the actual mobile charge carriers in circuits are electrons, which have a negative charge. But a flow of positive charge in one direction is equivalent to an equal flow of negative charge in the other direction. So the electrons in the circuit flow in the opposite direction to the direction of conventional current.

From the standpoint of electric power, components in an electric circuit can be divided into two categories: