A 2 kW heater, a 200 W TV and three 100 W lamps are all switched on from 6 p.m. to 10 p.m. What is the total cost at Rs. 5.50 per kWh?

Here for heater we have, P = 2kW, t = 4h

So energy consumed by heater, E = P x t = 2x4 = 8kWh


Here for TV, we have, P = 200W = 0.2kW, time 10pm – 6pm = 4h


So energy consumed by TV, E = P x t = 0.2x4 = 0.8kWh


Here for TV, we have, P = 100W = 0.1kW, t = 4h, number of lamp(n) = 3


So energy consumed by three lamps, E = n x P x t = 3x0.1x4 = 1.2kWh


Total energy consumed by heater, TV and three lamps = 8+0.8+1.2 = 10kWh


Cost of 1kWh = Rs. 5.50


Cost of 10kWh = Rs. 5.50 x 10 = Rs. 55


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