1. Power & Efficiency

2. Warm up
Wade and Kate run up the stairs of the CN Tower to raise money for charity. They climb a total vertical distance of 342 m. Wade has a mass of 70 kg and reaches the top in 25 minutes. Kate has a mass of 50 kg and reaches the top in 35 minutes.
How much work does each student do against gravity?
How much energy does Wade expend per second during the climb? What about Kate?

3. What is Power? Rate of doing work or transforming energy
Measured in Watts (W) 1 Watt (W) = 1 Joule per second (J/s)
Watts and kilowatts (1kW = 103 W) are usually used to measure power of household electrical appliances
Megawatts (1 MW = 106 W) are usually used to measure power of electric generating stations

4. Warm up
What is the difference between the light bulbs shown below?

5. Warm up

6. What is Efficiency?
When energy is transformed from one form to another, energy is lost
Efficiency is a measure of how much input energy is converted into the intended output.

7. What is efficiency?
Ratio of useful energy output to the energy input to operate the device
Usually unitless, and expressed as a percentage or decimal

8. Example
It takes 2010 Joules of electrical energy to operate a kettle. However, only 520 Joules of heat energy are required to heat the water. What is the kettle’s efficiency?

9. Homework
PG. 254 #1, 2, 3
PG. 249 #1, 2, 3