Year 9 Science · Unit 3 · Lesson 8
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Learning Goals
1. Explain what the words absorber, emitter and reflector mean for radiation. Which kind of surface is best at each?
Cause and effect: a lava lamp
Complete the chain. Each box is caused by the one before it.
Data: how well do materials conduct heat?
Thermal conductivity measures how easily heat passes through a material. A higher value means heat passes through more easily.
| Material | Thermal conductivity (W/m·K) |
|---|---|
| Copper | 401 |
| Carbon steel | 54 |
| Common brick | 0.6 to 1.0 |
| Sheep’s wool | 0.039 |
| Air | 0.026 |
Source: Engineering ToolBox, “Thermal Conductivity of Metals” and “Thermal Conductivity of Common Materials”.
2. Rank the five materials from best insulator to worst insulator.
3. Saucepans often have a copper base. How many times better a conductor is copper than carbon steel? Round to one decimal place.
Copper conducts times better
4. Ceiling insulation batts trap millions of tiny pockets of air. Use Table 1 to explain why trapped air insulates much better than a solid brick wall of the same thickness. Why must the air be trapped?
Investigation: black can or silver can?
A class filled two identical cans with water at 90 °C. One can was painted matte black; the other was polished silver. Both stood in the shade in a room at 20 °C.
| Time (min) | Matte black can (°C) | Polished silver can (°C) |
|---|---|---|
| 0 | 90 | 90 |
| 5 | 79 | 85 |
| 10 | 70 | 80 |
| 15 | 62 | 76 |
| 20 | 56 | 72 |
Source: sample class results.
5. Graph the black-can and silver-can temperatures against time on one grid, and label both curves.
6. Which can lost heat faster, and by which method of heat transfer? What does this tell you about matte black and polished silver surfaces as emitters?
7. The class repeats the test with both cans filled with cold water, standing in bright sunshine. Predict which can will warm up faster, and explain.
Scenario: a night in a tent
A hiker camps in the Snowy Mountains on a night when the air drops to 2 °C. She lies on a foam sleeping mat, inside a down sleeping bag, with a shiny emergency blanket over the bag.
8. Explain the three ways the hiker loses heat during the night. For each item of gear, name the method of heat transfer it reduces and explain how it works.