Question

In a certain city, electricity costs $0.20 per kw·h. what is the annual cost for electricity to power a lamp-post for 8.00 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

Part a)

per day electricity power consumed when 100 W bulb is used for 8 hours

`P = 8 * 100 = 800 Wh`

for one year consumption

`E = 365 * 800 = 292 kWH`

now the cost will be given

`cost = 0.20 * 292 = $ 58.4`

now when other energy efficient light is used

`P = 8 * 25 = 200 Wh`

for one year consumption

`E = 365 * 200 = 73 kWH`

now the cost will be given

`cost = 0.20 * 73 = $ 14.6`