# Electric Power

The rate at which electrical energy is dissipated into other forms of energy is called electrical power, i.e.,

# Rated values

On electrical appliances (bulbs, heater, etc.), wattage, voltage, etc, are printed called rated values. For example, if suppose we have a bulb of 40 W, 220 V then rated power (

*P*) = 40 W while rated voltage (_{R}*V*) = 220 V. It means that on operating the bulb at 220 V, the power dissipated will be 40 W or in other words 40 J of electrical energy will be converted into heat and light per second._{R}# Resistance of electrical appliance

If variation of resistance with temperature is neglected then resistance of any electrical appliance can be calculated by rated power and rated voltage, i.e., by using

# Power consumed

An electrical appliance (bulb, heater, etc.) consumes rated power (

*P*) only if the applied voltage (_{R}*V*) is equal to the rated voltage (_{A}*V*), i.e., if_{R}*V*=_{A}*V*. So_{R}*P*_{consumed}=*P*._{R}If

*V*<_{A}*V*, then . Also, we have So_{R}