Question

a household circuit, an electric bulb of 100 W is used for 10 hours and an electric heater of 1000 W for 2 hours everyday. Calculate the cost of using the bulb and the heater of 30 days if the cost of one unit of electrical energy is two rupees.

Answer 1

Energy used by the bulb = 100x10= 1000W=1KWh
Energy used by the heater=1000x2=2KWh
Total energy used in 1 day = 3 KWh
Energy used in 30 days = 30x3=90KWh
Cost of 1 KWh = RS.2
cost of 90KWh=2x90=Rs.180

Answer 2

Energy used by heater =100wx(10hx30days) =30000wh =30unit

Energy used by bulbs =1000w(2h ×30days) =60kwh =60units

Total Energy = 60+30 =90Units

Cost =90×2 =180 rupees