Year 9 Science · Unit 3 · Lesson 4

Energy Efficiency and Sankey Diagrams

Foundation Worksheet

Name

Date

Class

Learning Goals

Sort energy flows into useful outputs and waste outputs for different devices
Identify and name the key features of a Sankey diagram
Explain what arrow width represents in a Sankey diagram

Warm Up

Recall 10 marks

Sort it!

The energy flows below come from three different devices: a petrol car engine, an LED light globe, and an electric kettle. Write each energy flow into the correct column, either "Useful output" or "Waste output".

Kinetic energy of the car wheels (petrol engine) Heat from the car exhaust (petrol engine) Heat lost through the engine block (petrol engine) Sound from the engine (petrol engine) Light from the LED globe Heat from the LED globe's driver circuit Thermal energy transferred to the water (kettle) Sound of the kettle element humming Heat escaping through the kettle walls Electrical energy arriving at the kettle element

Useful output

Waste output

Your Turn

Recall 6 marks

Match each term to its description

Draw a line connecting each Sankey diagram feature on the left to its correct description on the right. Or write the matching letter in the "Your answer" column.

Sankey diagram feature	Your answer	Description
Input arrow		A. The point where the main arrow divides into useful and waste streams
Useful output arrow		B. The arrow that flows straight through, representing the energy that does the intended job
Waste heat arrow		C. The ratio of useful output to total input, expressed as a percentage
Width proportional to energy		D. The horizontal arrow entering from the left showing total energy supplied to the device
Split point		E. The downward-pointing arrow showing energy dissipated as thermal energy to the surroundings
Overall efficiency		F. The rule that a wider arrow represents more energy, you can compare flows visually

Show What You Know

1. In a Sankey diagram, the input arrow is 20 mm wide and the useful output arrow is 5 mm wide. What is the efficiency of this device? What can you conclude about the waste arrow?

Recall 2 marks

2. Explain in your own words why the total width of all arrows leaving a device in a Sankey diagram must always equal the width of the input arrow.

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?