Power:

Electricity is generally used to do a few sort of work, such as turning a motor or producing heat. Specifically, power is the rate at that work is complete, or the rate at which heat is generated.  The unit generally used to specify electric power is the watt. Within equations, you will find power abbreviated along with the capital letter P and watts, a units of measure for power that are abbreviated along with the capital letter W. Power is also define as the current (I) in a circuit times the voltage (E) across the circuit.  Equation (1-6) is a mathematical representation of this concept.

P = I x E         or        P = IE

Using Ohm's Law for the value of voltage (E), E = I x R

and using substitution laws, P = I x ( I x R)

power can be described as the current (I) in a circuit squared times the resistance (R) of the circuit.  Equation (1-7) is the mathematical representation of this concept.

P = I²R            (1-7)