In a certain city, electricity costs exist0.18 per kW middot h. What is the annu
ID: 539764 • Letter: I
Question
In a certain city, electricity costs exist0.18 per kW middot h. What is the annual cost for electricity to power a lamppost 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. (a) 100.-watt bulb exist 32.85 (b) 25-watt bulb exist 8.21 (c) A typical incandescent bulb costs exist0.89 and lasts for about a year: a typical energy efficient fluorescent bulb costs about exist3.49 and lasts for about 3 years. Is the additional cost of the fluorescent bulb justified? Here are the relevant values and conversion factors. Arrange them in a way that allows everything to cancel out except for dollars per year. 100. W (or 25 W) 1000 W/1 kW 0.18 dollars/kW middot h 5.50 h/1 day 365 days/1 yearExplanation / Answer
a)
power = 100 watt = 0.100 kw
time = 365 days * 5.50 hr/day = 2007.5 hr
energy usage = power * time = 0.100 kw * 2007.5 hr = 200.75 kw.hr
annual cost = 200.75 kw.hr * 0.18 per kw.hr = $36.14
Answer: $36.14
b)
power = 25 watt = 0.025 kw
time = 365 days * 5.5 hr/day = 2007.5 hr
energy usage = power * time = 0.025 kw * 2007.5 hr = 50.19 kw.hr
annual cost = 50.19 kw.hr * 0.18 per kw.hr = $9.03
Answer: $8.21
c)
total cost in incandescent bulb per year = $0.89 + $ 36.14= $37.03
since fluorescent bulb last for 3 years, its cost of buying in 1 year = 3.49/3 = $1.16
total cost in fluorescent bulb per year = $1.16 + $9.03 = $10.19
So, yes fluorescent bulb is cheaper overall
Answer: yes