Electrical Energy And Cost

Electrical energy consumed by an appliance is the product of its power rating and the time of operation, (E = P \times t), and the commercial unit kilowatt-hour corresponds to a power of one kilowatt sustained for one hour. Daily consumption is therefore (E_{day} = 2,\text{kW} \times 1.5,\text{h} = 3) kWh. Over 30 days the total becomes (E = 3 \times 30 = 90) kWh. The value 60 kWh wrongly uses 1 hour per day instead of 1.5 hours. The value 45 kWh halves the power, treating it as 1 kW. The value 120 kWh overstates the daily usage as 4 kWh. This applies the NCERT definition of the kilowatt-hour as the practical unit of electrical energy. A plausibility check confirms the figure: a 2 kW heater running ninety hours total in a month (1.5 hours times 30 days) must consume (2 \times 45 = 90) kWh, consistent with the stepwise result and with typical household billing magnitudes.