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 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.

Answer 1

we know power=work done/time taken
power*time= work
100watt=0.1kw
total work in a day= power* time
0.1*5.5=0.55kwh
for 1 year total.energy is 0.55*365=200.75kwh
cost is 200.75*0.13=26.0975dollars
for 25 watt it is 0.025*5.5*365*0.13=6.524375 dollars