Question

A typical cost for electric power is 10.5¢ per kilowatt-hour.

(a) Some people leave their porch light on all the time. What is the yearly cost to keep a 120-W bulb burning day and night? (Round your answer to two decimal places.)

(b) Suppose your refrigerator uses 485 W of power when it's running, and it runs 7 hours a day. What is the yearly cost of operating your refrigerator? (Round your answer to two decimal places.)

Answer 1

a) total energy consumed = Power x time

   time = 1 year = 365 days/year x 24 hr/day = 8760 hrs

total energy = 120W x 8760 hr = 1051200 Wh = 1051.2 kWh

total cost = 1051.2 x 10.5 = 11037.6 cents

In dollars = $110.38

b) daily energy consumption = 485 x 7 = 3395 Wh = 3.395 kWh

yearly consumption = 365 x 3.395 = 1239.17 kWh

cost = 1239.17 x 10.5 = 13011.34 cents

In dollars= $ 130.11