JAMB Physics 2017 Paper

Concept:The total cost is obtained by converting the combined power of all lamps into kilowatts, then multiplying by the running time and the energy tariff.Explanation:Find the total power used by the seven 40 W lamps.$7 \times 40 \, \text{W} = 280 \, \text{W}$.Find the total power used by the five 80 W lamps.$5 \times 80 \, \text{W} = 400 \, \text{W}$.Add the two values to get the overall power.Total power $= 280 \, \text{W} + 400 \, \text{W} = 680 \, \text{W}$.Convert the total power from watts to kilowatts.$680 \, \text{W} = \dfrac{680}{1000} \, \text{kW} = 0.68 \, \text{kW}$.Calculate the total electrical energy consumed in 12 hours.Energy $= 0.68 \, \text{kW} \times 12 \, \text{h} = 8.16 \, \text{kWh}$.Multiply the energy consumed by the cost per unit of electrical energy.Cost $= 8.16 \, \text{kWh} \times \text{N}7.00/\text{kWh}$.Cost $= \text{N}57.12$.Answer:The cost of running the lamps is $\text{N}57.12$, which is Option D.