Electric Energy—

The energy of a voltage source to flow a constant current through a resistor for a given time is called Electric Energy consumed in the circuit.

Let a voltage source ‘V’ supplies current ‘I’ through a resistor ‘R’, then         

The unit of Electrical Energy is ‘Watt-second’.

Since, this unit is very small so we use ‘Kilowatt-Hour’. This unit is also known as ‘Board of Trade (B.O.T.) Unit’ or ‘Commercial Unit of Electrical Energy’.

            1kWh=1 kW x ! hr

                        = 1000 W x 3600 s

            1kWh   = 3.6 x 10⁶ J

Power Rating—

The Power Rating of an Electrical appliance is defined as the electrical Energy consumed by the appliance if it is connected across the voltage according to the specification.