# Definition of Power

Power is defined as the rate of doing work**. **It is calculated by the following formulas:

1) P = V x I whereupon:

P= power measured in watts

V= voltage measured in volts

I = current measured in amperes or amps

2) It can also be expressed as P = I squared x R whereupon:

P= power measured in watts

I = current measured in amperes or amps and then squared

R= Resistance in the circuit of interest

3) It can also be expressed as P = V squared divided by R whereupon:

P= power measured in watts

V = voltage measured in volts and then squared

R= Resistance in the circuit of interest

It should be noted that formulas 2 and 3 are derived from formula 1 by algebraic solution.

A volt-ampere (VA) is the unit used for the apparent power in an electric circuit, equal to the product of root-mean-square (RMS) voltage and RMS current. In direct current (DC) circuits, this product is equal to the real power (active power) in watts. Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents).

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