1. Power & Efficiency
Power
Efficiency
Energy Resources 1

2. Power Work done per unit time Energy per unit time
P = work/time = energy / time
Units
Joules per second, Js-1
Watt, W 2

3. Example
A motor-driven lift carries 24 bricks to the top of a 3 m wall. If each brick weighs 10 N and takes 15 s to get to the top, how much is the power output of the motor?
If the motor has a power rating of 1000 W, how long will it take to lift 100 bricks? 3

4. Efficiency
Describes how much of the energy supplied is used than wasted.
Efficiency = useful output energy/total input energy
Output/input
No units
May be expressed in percentage 4

5. Example
A block is dragged up a slope with a force of 80 N. The block weighs 100 N and the slope is 20 m long and 10 m high. Calculate the efficiency of the work done. 5

6. Energy Resources Fuel Chemical (burning fuel) Thermal (boiling water)
Mechanical or Kinetic (turn turbines)
Electrical 6

7. Energy Resources Solar Light (sun shining on solar panels) Electrical7

8. Energy Resources Nuclear Nuclear (splitting of atoms)
Or combining of atoms
Thermal (boiling water)
Kinetic (turn turbines)
Electric 8

9. Energy Resources Wind Kinetic (Moving air)
Mechanical or Kinetic (turn turbines)
Electrical 9

10. Energy Resources Wave Kinetic (Moving water)
Mechanical or Kinetic (turn turbines)
Electrical 10

11. Energy Resources Hydroelectric Potential (water at a height)
Kinetic (Moving water)
Mechanical or Kinetic (turn turbines)
Electrical 11

13. Energy Resources Geothermal Thermal (Heat under the earth)
Thermal (boil water)
Mechanical or Kinetic (turn turbines)
Electrical 13

14. Questions Which energy resource does not boil water?
Which energy resource does not turn turbines?
Which energy resource does not rely on the sun? 14

15. Questions Which energy resources are renewable?
Which energy resources are non-renewable?
Which energy resource is the best? Why? 15