In a certain city, electricity costs $0.13 per kW·h. What is the annual cost for
ID: 475350 • Letter: I
Question
In a certain city, electricity costs $0.13 per kW·h. What is the annual cost for electricity to power a lamp-post for 7.50 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.
(c) 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
Total numbers of hours in a year = (365 days/yr) x (7.50 hrs/day)
Number of watt used = 100 *10^-3 kWatt * (365 days/yr) x (7.50 hrs/day)
Total cost = number of watt used * price
= (365 days/yr) x (7.50 hrs/day) x (0.100 kW) x ($0.13/ kWhr) = $35.59 / yr
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25 w is one-fourth of 100w, so the annual cost would be one quarter of the previous cost:
annual cost = $35.59 / yr /4 = $8.89 /yr
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In case of incandence bulb for 3 yrs you spend: 3 yr * $35.59/yr + $0.89*3 bulbs = $109.44
In case of fluorescent bulb you spend : $8.89 /yr * 3yr + 1* $3.49 = $30.16
The money spent if u use a fluorescent buld is less and the additional cost is justified.