In a certain city, electricity costs exist0.18 per kW middot h. What is the annu

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 = 385 days. (a) 100.-waltt bulb exist (b) 25-watt bulb exist 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? yes no

Explanation / 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

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