1. To understand energy efficiency and Sankey diagrams

2. To start Let’s review our homework Homework for this week
Print out the following revision sheets:
Q:\ physics\Year 9\ Year 9 Forces and Energy Topic summary
Revise for a test next week on all our work since the last test

3. Energy Efficiency TODAY we will be able to:
Draw and use a sankey diagram to show energy transfers
Continue describing energy transfers.
Explain useful and wasted energy transfers.
Be able to calculate the efficiency of energy transfers.

4. What has happened to the chemical energy in the wood on the fire?

5. Energy Transfers In the campfire example:
Lesson Aims:
In the campfire example:
Sound Energy
Light Energy
Thermal Energy
Chemical Energy in the wood
Only part of the Thermal energy is transferred to the fish to cook it. The rest is ‘lost’ heating the air.

6. Energy Efficiency
Lesson Aims:
If an energy transfer was 100% efficient, all of the energy is transferred into a useful form.
Unfortunately this is not normally the case!

7. Calculate Energy Efficiency
Lesson Aims:
Energy Efficiency is calculated using the equation:
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 % = 𝑈𝑠𝑒𝑓𝑢𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 𝑂𝑢𝑡𝑝𝑢𝑡 𝑇𝑜𝑡𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑝𝑢𝑡 ×100

8. Question Calculate the efficiency of this steam-diesel hybrid car.
Lesson Aims:
Calculate the efficiency of this steam-diesel hybrid car.
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦= 40𝐽 100𝐽 ×100%=40%
In The steam-diesel hybrid car, wasted energy is used to heat water and then produce steam; which is used as an input energy. The steam is used to power the car at slow speeds and conserves the diesel fuel.

9. Energy Efficiency Experiment
Lesson Aims:
We have the following equipment:
An electric motor
A winding system so the motor can be used to lift a weight.
An electrical energy meter (which measures the energy transferred when a circuit is switched on)
5 Different masses
A metre rule.
In pairs you have 2 minutes to discuss and decide what experiment (s) you would carry out to see how efficient the motor is.

10. Prepare Results Table What are we controlling each time?
Lesson Aims:
What are we controlling each time?
What are we measuring?
What do we need to record?

11. Motor Efficiency Experiment
Lesson Aims:
Aim: To compare the electrical energy supplied to the motor with the work done lifting a load.
Method:
Draw a diagram of the equipment.
The motor will lift different masses ___m
We can measure the electrical energy supplied using an energy meter.
How do we calculate work done?
𝑊𝑜𝑟𝑘 𝐷𝑜𝑛𝑒 =𝐹𝑜𝑟𝑐𝑒 ×𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒

12. Calculate Energy Efficiency
Lesson Aims:
Energy Efficiency is calculated using the equation:
𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 % = 𝑈𝑠𝑒𝑓𝑢𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 𝑂𝑢𝑡𝑝𝑢𝑡 𝑇𝑜𝑡𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑝𝑢𝑡 ×100
Calculate the efficiency of the electric motor for each different mass lifted.
Is the efficiency always the same? If not, why do you think it changes?
What forms of energy are not useful in our system?