Electrical Power

REAL POWER [Actual power]:
In AC circuit  because of phase difference between current and voltage the average value of real power is given by 
                          P=V*I*cos(θ);
 and its measure unit is Watt(W).

REACTIVE POWER [Useless power]:
Power merely absorbed and returned in load due to its reactive properties is referred to as reactive power.The average value of reactive power is given by 
                       Q = V *I*sin(θ);
 and expressed in unit VAR. 

Apparent Power:
Total power in an AC circuit, both dissipated and absorbed/returned is referred to as apparent power.
                    S=V*I; 
and is expressed in unit as VA. 

Apparent Power = √ (Real power^2 + Reactive Power^2);

IMPORTANT NOTES:
- Resistor absorbs the real power and dissipates in the form of heat and light.
- Inductor absorbs the reactive power and dissipates in the form of magnetic field.
- Capacitor absorbs the reactive power and dissipates in the form of electric or electrostatic field.