Physics 2017 JAMB Past Questions - Question 33: What is the cost of running five 50W lamps and four 100W lamps for 10 hours if electrical energy costs 2 kobo per kWh ?

Correct Answer

A

Explanation

To calculate the cost of running the lamps, we need to determine the total energy consumed by the lamps and then multiply it by the cost per kilowatt-hour (kWh).

First, let's calculate the total power consumption of the lamps.

For the five 50W lamps:
Total power = 5 lamps * 50W/lamp = 250W

For the four 100W lamps:
Total power = 4 lamps * 100W/lamp = 400W

Now, let's calculate the total energy consumed by the lamps in kilowatt-hours (kWh):

Total energy = (Total power * Total time) / 1000
            = ((250W + 400W) * 10 hours) / 1000
            = (650W * 10 hours) / 1000
            = 6500 watt-hours / 1000
            = 6.5 kWh

Finally, let's calculate the cost:

Cost = Total energy * Cost per kWh
      = 6.5 kWh * 2 kobo/kWh
      = 13 kobo

Therefore, the cost of running five 50W lamps and four 100W lamps for 10 hours, with electrical energy costing 2 kobo per kWh, is 13 kobo.