Voltage and current are two basic parameters of an electric circuit. But, only voltage and current are not sufficient to express the behaviour an electric circuit element. We essentially need to know, how much electric power, a circuit element can handle. All of us have seen that a 60 watts electric lamp gives less light than a 100 watts electric lamp. When we pay electric bill for electricity consumption, we are actually paying the cahrges for electric power for a specified period of time. Thus