Year 9 Science · Unit 3 · Lesson 11
Challenge Worksheet
Learning Goals
Read the graph
Study the bar chart showing the efficiency of four common devices. Then answer the three questions below.
(a) Which device converts the greatest proportion of its input energy into useful output? What happens to the remaining energy?
(b) A petrol car engine is only 25% efficient. Using the law of conservation of energy, explain where the other 75% of the chemical energy in petrol goes.
(c) An incandescent globe is only 5% efficient while an LED globe is 90% efficient. Both produce the same amount of light. Compare the amount of waste thermal energy produced by each, and explain the consequence for running costs.
Find the mistake
A student wrote this answer
"When you use an inefficient electric heater, a lot of energy is destroyed as waste. This wasted energy just disappears. Also, convection can occur in solids, for example, heat moves through a metal rod by convection. Copper is a great material to heat water in a solar system because it has a very high specific heat capacity. Finally, thermal expansion happens because each atom actually grows bigger when it absorbs heat energy."
1. The student makes FOUR scientific errors. List each error and identify which concept from Lessons 1–10 it relates to.
2. Rewrite the student's paragraph so that all four errors are corrected. Your version must be scientifically accurate and use the correct terminology.
Wrap Up
In one sentence, what was the main idea of this checkpoint?