power

Power is nothing but rate of doing work,that is nothing but joule per second.If one joule of work can be done in a second it can be defined as one watt.

                       watt = energy / time

                              = joule / second. 

                           we can write it as

                              = (joule / charge) * (charge / second)

                              =      volt             * current

             so power can be defined as volt*current, it can be called as watt.

In dc supply system we can say power as watt only because it has no power factor problem which is present in ac supply system.

In ac supply system there is a phase difference between voltage and current.depending upon load i.e. capacitive , resistive,inductive loads it can be varied as leading, unity,lagging power factor.

                             power

                                 1.active power.

                                 2.reactive power.

                                 3.apparent power.

1.Active power :It is the product of ac voltage, current magnitude(average values not rms )values and cosine angle of current and voltage waves.

                          P=VI cos ∅ , unit = watts

2.Reactive power:It is the product of ac voltage, current magnitude(average values not rms )values and sine angle of current and voltage waves.

                          Q=VI sin ∅ , unit= var

3. Apparant power:It is the product of ac voltage , current magnitude(average values not rms).

                      

                           S = VI ,unit , unit = volt amp