The relationship between current, power and voltage comes from the application of energy considerations to the motion of electric charges. The electric potential energy (voltage) is the amount of energy required to move a charge through an energy difference. The flow of electric charge is measured by the amount of charge moved per second. If the amount of charge is measured in Coulombs (C), then the flow of current is measured in the Ampere (A).

The electric potential energy is given by the relationship

V = IR where V is the electric potential energy, I is the current in Amps, and R is the resistance of the circuit. The resistance is actually any device which is converting the electrical energy to some other form of energy. The rate of this energy conversion by the resistance is known as the electric power. There are several relationships that can define electric power consumption:

P = IV

P = I^2R and

P = V^2/R are three.

Of these, the first is the most useful for the problem in question:

P = IV provides

I = P/V = (303W)/(120V) = 2.53 A