Year 9 Science · Unit 3 · Lesson 4
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "How efficient is a small electric motor at converting electrical energy into kinetic energy, and can we use the results to draw a Sankey diagram?" Plan the investigation below.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables, list at least 3) | |
| What I will measure (dependent variables, include how you measure electrical energy input AND kinetic energy output) | |
| How I would calculate efficiency from my measurements | |
| How I would use my results to draw a Sankey diagram (describe what each arrow represents and how you would set its width) | |
| One limitation of this experiment and how it might affect results |
1. A small electric motor receives 50 J of electrical energy and produces 7 J of useful mechanical (kinetic) energy. The remaining energy is lost as waste heat. (a) Calculate the waste energy. (b) Calculate the efficiency of the motor as a percentage. (c) Using a scale of 1 cm = 10 J, state the width of each arrow in a Sankey diagram for this motor. Show all working.
2. Based on your efficiency calculation in Question 1, describe what the Sankey diagram for this motor would look like. Which arrow would be widest? What does this reveal about where the energy goes? If you were an engineer, what one change would you make to improve the motor's efficiency, and how would that change the widths of the arrows in the diagram?
Wrap Up
In one sentence, what was the main idea of this lesson?