Physics 2013 JAMB Past Questions - Question 40: A house has ten 40W and five 100W bulbs .How much will it cost the owner of the house to keep them lit for 10hours if the cost of a unit is N5?

Correct Answer

C

Explanation

units of energy used = power x time(40x10+100x5)x10(400+500)x10900x10900wh = 9kwh = 9 unitscost of one units = 9x5N = 45N
To calculate the cost of keeping the bulbs lit for 10 hours, we need to determine the total power consumption of all the bulbs and then multiply it by the cost per unit.

Let's calculate the total power consumption of the bulbs first:

For the ten 40W bulbs:
Total power consumption = 10 bulbs * 40W/bulb = 400W

For the five 100W bulbs:
Total power consumption = 5 bulbs * 100W/bulb = 500W

Now, let's calculate the total power consumption of all the bulbs:
Total power consumption = 400W + 500W = 900W

Since the cost of a unit is N5, we can calculate the cost of keeping the bulbs lit for 10 hours:
Cost = Total power consumption * Time * Cost per unit
Cost = 900W * 10 hours * N5/unit = 9000 watt-hours * N5/unit

Please note that the unit of watt-hours is not directly comparable to the unit of Naira (N). To convert watt-hours to kilowatt-hours (kWh), we divide by 1000:
Cost = (9000 watt-hours / 1000) * N5/unit = 9 kWh * N5/unit

Therefore, the cost for the owner of the house to keep the bulbs lit for 10 hours would be 9 times the cost per unit, which is 9 * N5 = N45.