1. 1 2 3 Electrical Energy Electrical Energy Electrical Energy
Useful kinetic energy
Useful sound energy
Useful heat energy 1 2 3
Electrical Energy
Electrical Energy
Electrical Energy
Wasted light energy
Wasted heat energy
Wasted heat energy

2. Lesson Title
Efficiency

3. Success criteria Compare devices in terms of their efficiency
Draw a sankey diagram of an immersion heater
Calculate the efficiency of an immersion heater
Suggest explanations for different efficiencies of heater

4. Recap from last lesson Efficiency = useful energy (or power) out
total energy (or power) in
Sometimes this is expressed as a %
Efficiency = useful energy (or power) out x100
total energy (or power) in

5. Mini Review Teacher notes
This multiple-choice activity provides an opportunity for students to practise using the energy efficiency equation. Students could answer each question in their books before revealing the answer on the IWB.

6. Applying our knowledge
We can calculate the efficiency of any system as long as we can measure the energy inputs and outputs. What will happen if we set up this circuit?

7. Useful energy out = m x C x θ Efficiency = m x C x θ V x I x t
Useful formulae:
V = IR
Electrical power = VI = I2R = V2/R
Electrical energy = Power x Time = VIt = I2Rt = (V2/R)t
Heat energy = mass x specific heat capacity x temperature rise
Total energy in = V x I x t
Useful energy out = m x C x θ
Efficiency = m x C x θ
V x I x t

8. Variables
Independent
Dependent
Control

9. What do you think will make the most efficient heater?

10. Draw your results table
Change in temperature over ~5 minutes
You will need to also record:
Time
Voltage (average)
Current (average)
Mass of water used
Length and thickness of wire

11. Our experiment Collect your equipment
Do pre-measurements (things that wont change throughout the experiment)
Set up the circuit
Get it checked
Start the experiment!

12. Group results Group Length of wire Thickness of wire
Average temp rise (°C)
Efficiency of the heater 1 2 3 4 5 6 7 8 9 10 11 12

13. Conclusions
What was the efficiency of your heater How did this compare to other heaters? Can you explain what made the difference?

14. Evaluating results
In order to assess the quality of your evidence, you need to consider the following things:
Reliability
Validity
Accuracy

21. Evaluating an experiment
Were your results reliable? How could you improve them?
Were your results valid?
Were your results accurate? What kinds of errors were there (systematic or random) and how could you reduce them?

22. Apply to Demonstrate
Now you have calculated the efficiency of the heater, describe what you have found out in the form of a Sankey Diagram.
Then Kerboodle exam questions – finish for homework (they will help you to revise for the mock!)

23. Plenary What did you learn today? What did you find difficult?
What do you feel most confident in?
How do you feel now?