Year 9 Science · Unit 3 · Lesson 11
Foundation Worksheet
Learning Goals
Match each term to its meaning
Write the letter of the matching meaning in the middle column. Each letter is used once.
| Term | Letter | Meaning |
|---|---|---|
| Conduction | A. Heat transfer by electromagnetic waves, which needs no medium | |
| Convection | B. Useful energy out ÷ total energy in × 100% | |
| Radiation | C. Energy that has spread out into the surroundings as heat and cannot easily be used again | |
| Specific heat capacity | D. Heat transfer through a solid, as particles pass on their vibrations | |
| Law of conservation of energy | E. A flow diagram in which the width of each arrow shows an amount of energy | |
| Efficiency | F. The energy needed to raise the temperature of 1 kg of a substance by 1 °C | |
| Sankey diagram | G. Heat transfer through a liquid or gas, as warmer fluid rises in a current | |
| Dissipated energy | H. Energy cannot be created or destroyed, only transferred or transformed |
1. A student says: “An electric kettle that is 80% efficient wastes 80% of its energy.” What does 80% efficient really mean, and where does the rest of the energy go?
Sort it: which equation would you use?
Write each situation in the box for the equation you would use to answer it. Each box gets two situations.
Work done: W = F × d
Efficiency
Heating: Q = mcΔT
2. Calculate the work done by the tractor on the log. Show your working.
Work done J
3. For the torch, calculate (a) the waste energy and (b) the efficiency. Name the form most of the waste energy takes.
(a) Waste energy J
(b) Efficiency %
Investigation: which lining makes the best solar oven?
A class built three identical cardboard-box solar ovens with clear plastic lids. They lined the inside of one box with black paper and one with white paper, and left one as bare brown cardboard. Each oven held a small tray with 0.20 kg of water at 20 °C, and all three sat side by side in full sun for 30 minutes. Use c = 4,200 J/kg·°C for water (the unit’s value).
| Lining | Final temperature (°C) | Temperature rise (°C) | Energy taken in by the water (J) |
|---|---|---|---|
| Black paper | 56 | 36 | 30,240 |
| Brown cardboard | 44 | ||
| White paper | 38 |
Source: sample class results.
4. Complete Table 1 using Q = mcΔT. The black lining is done for you: 0.20 × 4,200 × 36 = 30,240 J.
5. Which lining worked best? Explain why, using what dark and light surfaces do to radiation.
6. About 90,000 J of sunlight entered each oven through its lid in the 30 minutes. Calculate the efficiency of the black-lined oven at heating the water, and name two ways the rest of the energy escaped.
Efficiency %
7. A pie at the footy. At a night football match in Ballarat, the air is 8 °C and a breeze is blowing. A fan buys a meat pie at 85 °C and rests it, in its paper bag, on a cold metal railing while he takes a photo, then forgets it until the final siren. Describe how the pie loses heat. Name where conduction, convection and radiation each happen, say which way the heat flows, explain what happens to the pie’s thermal energy, and predict the pie’s temperature at the end of the game.