In a certain city, electricity costs $0.16 per kW⋅h. What is the annual cost for electricity to power a lamppost for 7.50 h per day with a 100. W incandescent light bulb versus an energy efficient 25 W fluorescent bulb that produces the same amount of light? Assume 1 year=365 days.

annual cost for electricity for 100 W is $43.8

annual cost for electricity for 25 W is $10.95

Explanation:

given data

electricity costs = $0.16 per kW⋅h

duration lamppost = 7.50 h per day

to find out

What is the annual cost for electricity for 100 W and 25 W

solution

we know power consumption 1 day for 100 W = 100 * 7.50

and power consumption in 1 year = 365 * 100 * 7.50 = 273750 watt hour

and we know 1 watt hour = 0.001 Kw hour

so that 273750 watt hour = 273.750 KWh

and 1 kWh = $0.16

so 273.750 KWh = 0.16 * 273.750 = $43.8

annual cost for electricity for 100 W is $43.8

and

power consumption 1 day for 25 W = 25 * 7.50

and power consumption in 1 year = 365 * 25 * 7.50 = 68437.5 watt hour

and we know 1 watt hour = 0.001 Kw hour

so that 68437.5 watt hour = 68.4375 kWhour

and 1 kWh = $0.16

so 68.4375 kWh = 0.16 * 68.4375 = $10.95

annual cost for electricity for 25 W is $10.95