JAMB - Physics (2017 - No. 41)
What is the cost of running seven 40 W lamps and five 80 W lamps for 12 hours of the electrical energy cost N7.00kWh?
N80.00
N45.36
N65.00
N57.12
Explanation
Seven 40W lamps = 7 × 40 = 280W
Five 80W lamps = 5 × 80 = 400W
Total power = 280W + 400W
= 680W
= \(\frac{680KW}{1000}\) = 0.68KW
The kilowatt hour = 0.68 KW × 12 hrs
= 8.16 KWh
Cost is N 7 per KWh
So the cost of running them = 8.16KWh × N 7/KWh
= 57.12
Five 80W lamps = 5 × 80 = 400W
Total power = 280W + 400W
= 680W
= \(\frac{680KW}{1000}\) = 0.68KW
The kilowatt hour = 0.68 KW × 12 hrs
= 8.16 KWh
Cost is N 7 per KWh
So the cost of running them = 8.16KWh × N 7/KWh
= 57.12
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