1. The kW-hr is not a unit of power. What is it?
2. You inadvertently leave the light in your room at home for an hour, incurring the wrath of a parent for your profligate habits. If electricity costs 14 cents/kW-hr and your room is lighted by a 100W bulb, what did it cost to leave the light on for the full hour? What would it cost for the week?
3. The fluorescent tubes overhead are rated at 40 W. At 14 cents/kW-hr, how much does it cost to light this room daily from 7 a.m. to 3 p.m.?
4. Atilla-the-wife has a hand-held hair dryer rated at 1200 W and is used in a 120 V outlet. a) How much current does it draw? What is the cost for 20 minutes of use?
5. The Torkelsons heat their hot water with electricity. Cold water enters the tank at 6 degrees C and leaves at 65 degrees C. If their teenage son showers for 20 minutes and the shower uses 8 liters/minute, how much does junior's shower cost? Assume the cost of electricity to be 14 cents/kW-hr. [Hint: Find how much water is used, the change in temperature of the water, and the specific heat of the water. These data will give you some idea of the energy needed. If you express this quantity in Joules, you can use the conversion found in #1 above to determine the number of kW-hr needed. Now find the cost.]
Last edited 12/24/05