Question

In a house two 60 W electric bulbs are lighted for 4 hours, and three 100 W bulbs for 5 hours everyday. Calculate the electric consumed in 30 days.

Answer 1

Power of bulb 1, P₁ = 60 W
Duration that it was lit, t₁= 4 h
Electric energy consumed by two bulbs, E₁ = 2 x P₁ x t₁
                                                                     = 2 x 60 x 4
                                                                     = 480 Wh

Power of bulb 2, P₂ = 100 W
Duration that it was lit, t₂= 5 h
Electric energy consumed by three bulbs, E₂= 3 x P₂x t₂ = 3 x 100 x 5 = 1500 Wh

Total electric energy consumed in 30 days, E = 30 x (E₁+ E₂)
                                                                     E = 30 x (480 + 1500)
                                                                     E = 30 x 1980                                                      
                                                                     E = 59400 Wh
                                                                     E = 59.4 kWh