Electric power is the rate at which energy is expanded. It is denoted by either P or p.
If one joule of energy is expended in transferring one coulomb of charge through the circuit, then the rate of energy expenditure in transferring one coulomb of charge per second through the circuit is one watt. So, the SI unit of electric power is watt or joule per second.
This absorbed power must be proportional both to the number of coulombs transferred per second or per second or current and to the energy needed to transfer one coulomb through the element or voltage.
In practice, watt is often found to be inconveniently small, consequently the unit kilowatt is used.
1kW = 1000 watts
1MW = 1000kW
All appliances and devices used in domestic purpose as well as industrial purposes are rated in watt. For example, 100 watt lamp, 5 kW motor, etc
According to Ohm’s law V = IR
P = VI
P = V2/R
P = I2R