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JAMB Physics 2010 Paper

Question : 44

Total: 47

In the diagram above, a 200 W bulb is lighted by a 240 V a.c mains supply. If 1kwh is sold at N40, the cost of keeping the bulb lighted for a day is?

Solution:

Concept:

The cost of electrical energy depends on the total energy consumed and the price per unit (kWh).

Explanation:

Power of the bulb is

200\,\text{W}

Time of use in one day is

24\,\text{h}

Energy consumed is calculated as product of power and time:

200 \times 24 = 4800\,\text{Wh}

Convert watt-hours to kilowatt-hours:

4800\,\text{Wh} = 4.8\,\text{kWh}

1\,\text{kWh}

costs

\mathrm{N}40

, then

4.8\,\text{kWh}

costs

4.8 \times 40 = \mathrm{N}192

Answer:

\mathrm{N}192.00

(Option B).

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