Efficiency and Sankey Diagrams
IGCSE Edexcel Physics
4.4-4.5 Efficiency and Sankey Diagrams
Key Concepts:
$\text{efficiency} = \frac{\text{useful output}}{\text{total input}} \times 100\%$.
Section A: Efficiency
1. A motor takes in 500 J and gives out 150 J useful energy. Calculate efficiency.
[2]
2. A heater is 70% efficient. If input energy is 800 J, calculate useful output.
[3]
Section B: Sankey Diagrams
3. Explain what a Sankey diagram shows.
[2]
Total marks: 7
Mark Scheme
1.
$150/500 \times 100 = 30\%$ [2]
2.
Useful output = $0.70 \times 800 = 560\,J$ [3]
3.
Shows energy transfers with arrow width proportional to energy [2]