The electric appliances which we use in houses or in offices are generally marked with the voltage by which it runs and the electric power in watt. We know the rate of work done or the rate of energy conversion is called power. Therefore, the rate at which energy is converted into other forms in an electric device is its power.

Therefore,** power = [Work done/time] = [energy convened/time]**

So, **P = W/t**

Substituting the value of W from equation we get,

P = VI

Applying Ohm’s law P can be expressed in terms of V, I and R as below-

**P = VI = I ^{2}R = V^{2}/R**

We know the unit of power is watt (W). In the calculations of electric energy generally kW, MW etc. are used instead of waft 1 kW = 10^{3} W and 1 MW = 10^{6} W.

The power of some of the electric appliances which we use in our houses is mentioned below. The power of an electric bulb is generally 40, 60 and 100 W. The power of an electric fan is found to 65-75 W commonly. Power of a television is generally 60-70 W. The energy saving bulbs which we use now-a-days has power of 11-30 W.

Besides this, we use refrigerator, heater, iron etc. in houses- their power is more. So, it is commended not to use these appliances during peak hour.