Electricity is nothing but energy, so its unit of measurement is a measure of energy. But it is not measured in the standard unit of energy measurement, the Joule. It is instead measured in a roundabout way in kilo-Watt-hour. This is ironically to make life easy for the consumers. And how is that? Every appliance comes with a wattage, a measure of the 'power' it consumes (not the energy). A bright bulb is 100 W. Wattage means the number of energy units it consumes per second. Now, if I keep the bulb on for an hour, the energy consumed is : 100 * 3600 Joules. However, in the roundabout measure of energy, it is very conveniently, 100 Watt-hour (no multiplication :)).
The charges in India for a kWh of electricity is around Rs 2. So if you keep 10 bulbs on for one hour, it will cost you Rs. 2.
