ELECTRIC POWER
The rate of doing work is called as power. Also we can define power as rate of consumption of energy.
Power = energy/time(T) -(1)
So electric power can be defined as rate of consumption of electric energy.
Equations of electric power
From joules law electrical energy produced = I²RT = VIT = V²T/R
From (1) electric power (P)= I²RT/T = I²R
Power (P) = I²R
or
P = VIT/T = VI
Power (P) = VI
or
P= V²T/R/T = V²/R
Power(P) = V²/R
SI unit of power is watt(W). Since watt is very small for practical purposes we use kilowatt as unit of electric power.
Commercial unit of electric energy
Electrical energy can be expressed as product of power and time
Electrical energy = power x time
So commercial unit of electrical energy from the above equation can be given as kilowatt hour (kWh)