1. Can you finish the questions you started last lesson?
Do now!
Can you finish the questions you started last lesson?

2. Energy transfer (change)
A lamp turns electrical energy into heat and light energy

3. Sankey Diagram
A Sankey diagram helps to show how much light and heat energy is produced

4. Sankey Diagram
The thickness of each arrow is drawn to scale to show the amount of energy

5. Sankey Diagram
Notice that the total amount of energy before is equal to the total amount of energy after (conservation of energy)

6. Efficiency
Although the total energy out is the same, not all of it is useful.

7. Efficiency Efficiency is defined as
Efficiency (%) = useful energy output x 100
total energy input

8. Example
Efficiency = 75 x 100 = 15%
500

9. Energy efficient light bulb
Efficiency = 75 x 100 = 75%
100
That’s much better!

10. More complex examples

11. You then did some questions!

12. Thermal energy transfer

13. Thermal Energy Transfer

14. Heat can travel by Convection

15. Heat can travel by Convection
A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.

16. Examples of Convection

17. Heat cannot travel in solids by convection.
Why?

18. Draw the sentence A fluid is a liquid or gas
When a fluid is heated it expands
This makes it less dense than the surrounding fluid
The heated fluid rises because it is less dense
Cooler fluid takes its place
In this way a circular convection current can be formed
Convection currents can occur in kettles
Convection currents also cause wind.