Question

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

Answer 1

Power 1 =100 W
Power 2 =1000 W
Time 1 =10 hrs
Time 2 =2 hrs
Energy 1= 100×10
= 1000 Wh
= 1 Kwh
Energy 2 = 1000×2
= 2000 Wh
= 2Kwh
Total energy in 30 days = (1+2)×30
=3×30
=90 Kwh
Cost in 30 days = 90 × 2
= 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