Define active, reactive and Apparent power ?

Answer: Active Power, it is the true power which is actually consumed in the circuit. We can say that it is the product of voltage and current and power factor.
 Reactive power: It is the product of voltage current and sin of the phase angle.
Apparent power: It is the product of voltage and current.

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Real Power: (P)
Real Power is the actual power which is really transferred to the load such as transformer, induction motors, generators etc.
Reactive Power: (Q)  
Also known as (Use-less Power, Watt less Power)
The powers that continuously bounce back and forth between source and load is known as reactive Power (Q).

Apparent Power: (S)
The product of voltage and current if and only if the phase angle differencesbetween current and voltage are ignored.
Total power in an AC circuit, both dissipated and absorbed/returned is referred to as apparent power.

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