Year 9 Science · Unit 3 · Lesson 8
Foundation Worksheet
Learning Goals
1. Why can convection happen in water and in air, but not in a steel bar?
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
Convection happens in solids, because their particles are tightly packed and pass energy to their neighbours.
Correct it:
Radiation needs a medium to travel through, so it cannot cross a vacuum.
Correct it:
Metals are good thermal conductors because they have free electrons that move rapidly and carry kinetic energy.
Correct it:
Only very hot objects, like the Sun or a fire, give off thermal radiation.
Correct it:
A dull black surface is a better emitter of radiation than a shiny silver surface.
Correct it:
Fill the gap
Choose the correct word from the word bank. Each word is used once. Two words will not be used.
A fish tank has a heater near the bottom. The water next to the heater warms up. Its particles move faster and spread out, so the water and becomes less . The warm water , and cooler, denser water to take its place. This circulating flow is called a convection . Convection can only happen in , which are liquids and gases.
2. Explain why several thin layers of clothing keep you warmer on a cold day than one thick layer of the same total thickness. Use conduction and convection in your answer.
3. A student says: “Heat rises, so the best place for a room heater is near the ceiling.” Identify the error in this reasoning. Where should the heater go, and why?
Investigation: which rod conducts best?
A class stuck a small blob of wax to one end of five rods of the same length and thickness. They held the other end of each rod in the same hot water bath and timed how long the wax took to melt. They stopped each test at 600 s.
| Rod material | Time for the wax to melt (s) | Rank (1 = best conductor) |
|---|---|---|
| Steel | 190 | |
| Wood | did not melt in 600 s | |
| Copper | 45 | |
| Glass | did not melt in 600 s | |
| Aluminium | 70 |
Source: sample class results.
4. Complete the Rank column of Table 1. Give glass and wood the same rank.
5. Name TWO things the class kept the same to make this a fair test, and say why each one matters.
6. Use particle theory to explain why the three metal rods melted their wax much faster than glass and wood did.
Scenario: cooking pasta
Maya boils pasta water in a steel pot with a copper base, on a glowing electric cooktop. The pot has a plastic handle. The lid is off.
7. Describe how heat reaches the water at the top of the pot, and how heat escapes from the pot. Name conduction, convection and radiation where each one happens, and explain why the handle is made of plastic.