Electric power is the rate at which electrical energy is transferred by an electric circuit per unit of time. The watt, or one joule per second, is the SI unit of power. Electric generators are the most common source of electricity, but other sources such as electric batteries can also be used.
The coulomb (C) is the SI unit of electric charge, and it is equal to the charge contained in almost 6 10 18 electrons. (An electron has a negative charge of 1.6 10–19 C, as we know.) The ampere (A) is a unit of electric current named after the French scientist Andre-Marie Ampere (1775–1836). The flow of one coulomb of charge per second, or 1 A = 1 C/1 s, is equal to one ampere. Microampere (1 A = 10–6 A) and milliampere (1 mA = 10–3 A) are used to measure small amounts of current. An ammeter is a device that measures electric current in a circuit. In a circuit when the current is to be measured, it is always linked in series.
What is electric power? Derive 
