Please explain calculations, thank you. In a certain city, electricity costs $0.

Question

Please explain calculations, thank you.

In a certain city, electricity costs $0.10 per kW . h. What is the annual cost for electricity to power a lamp-post for 5.50 hours per day with (a) a 100.-watt incandescent light bulb (b) an energy efficient 25-watt fluorescent bulb that produces the same amount of light? Assume 1 year = 365 days. 100.-watt bulb 25-watt bulb A typical incandescent bulb costs $0.89 and lasts for about a year; a typical energy efficient fluorescent bulb costs about $3.49 and lasts for about 3 years. Is the additional cost of the fluorescent bulb justified?

Explanation / Answer

a) Power consumption in 1 day = 100*5.5 watt hours
Power consumption in 1 year( 365 days)= 100*5.5*365
=200750 watt hour
1watt hour= 0.001 Kw hour
so , 200750 watt hour = 200.750 Kw hour
1 Kw hour = $0.10
so, 200.750 Kw Hour = 200.75 * 0.1 = $ 20.075

b)Power consumption in 1 day =25*5.5 watt hours

Power consumption in 1 year( 365 days)= 25*5.5*365
= 50187.5watt hour

1watt hour= 0.001 Kw hour
so , 50187.5 watt hour = 50.187 Kw hour
1 Kw hour = $0.10
so, 50.187 Kw Hour costs 50.187 * 0.1 = $ 5.01875

c) An incandescent bulb for $0.89 and works for 1 year
That means in 3 years $0.89*3= $2.67
Plus the electricity cost = $2.67+ $20.075 = $22.745

For 3 years a flurescent lamp costs $3.49
Plus the electricity cost= $3.49+$5.01875 = $ 8.50875

Since the total cost is low, the flurescent bulb's extra cost is justified.

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