HOME ENERGY AUDIT: POWER WORKSHEET ANSWER KEY

Created for the NTEP II program on behalf of the National Renewable Energy Laboratory in Golden, Colorado.

1. Explain how work and energy are affected by power.

Power is the rate at which energy is transferred and power is the measure of how fast work can be done.

2. Using the equation for power, determine how much power in watts is involved if 300 joules of work are done in 10 seconds.

Power = Work /Time-----(P=W/T )therefore 300 joules/10 seconds= 30 joules/second or 30 watts.

3. About how many times longer would a 10 watt lightbulb be able to burn compared to a 100 watt bulb with the same energy?

100 watts /10 watts = 10 or 10 times longer

4. Rank the following items from lowest power requirement to highest power requirement.

___3rd____	a 100 watt lightbulb burns for 2 hours (100/2 = 50 a 100 watt light bulb burns for 2 hours)
___2nd____	a 40 watt lightbulb burns for 4 hours (40/4 = 10 a 40 watt light bulb burns for 4 hours)
___5th____	a 1500 watt hair dryer is used for 0.5 hours (1500/.5 = 3000 a 1500 watt hair dryer is used for 0.5 hours)
___4th____	a 500 watt microwave operates for 0.5 hours (500/.5 = 1000 a 500 watt microwave operates for 0.5 hours)
___1st____	a 15 watt compact fluorescent light burns for 10 hours (15/10 = 1.5 a 15 watt compact fluorescent light burns for 10 hours)

5. Calculate how much it would cost to operate a 1000 watt spotlight for one 8 hours if 1 kilowatt-hour costs $0.15.

1000= 1 kilowatt x 8hours = 8 kilowatt hours x $0.15 = $1.20

6. How do the lighting requirements differ between the hallway, the gym, and the library of your school? How would you suggest these areas be lit?

 Answers will vary depending on the school.