AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2022: Question 5

💡 Key knowledge

• Black/dark surfaces absorb infrared radiation better than white/shiny surfaces.
• A fair test keeps all variables the same except the one being investigated.
• On a temperature–time graph, steeper gradient = faster temperature increase.
• Temperature becomes constant when energy in = energy out.

🧠 Exam technique

• For “improvements”, give both the change and why it improves the test.
• For graph questions, quote evidence from the graph, not general knowledge.
• For 4-mark explanations, build a sequence: absorb energy → warm up → losses increase → equilibrium.

✅ Correct answers

The mark scheme allows any two pairs from the following:

• Place each flask the same distance from the infrared lamp so the intensity of infrared radiation reaching each flask is the same.
• Use flasks of the same shape and size so the surface area is the same.
• Use equal volumes of water (or equal masses of water) because the volume of water affects the rate at which the temperature increases.

🧠 How to write a full-mark answer

Do not just list changes. You must explain why each change improves the method.

Model answer:

1. Put the two flasks the same distance from the infrared lamp so they both receive the same intensity of infrared radiation.

2. Use the same volume of water in each flask so the amount of water does not affect how quickly the temperature rises.

💡 Why these improvements matter

• If one flask is closer to the lamp, it gets more radiation, so colour would not be the only variable.
• If flasks are different shapes/sizes, they may absorb and lose heat differently.
• If one flask has more water, it usually heats more slowly.

❌ Common errors

• Saying “repeat the experiment” without explaining how that improves reliability. This is sensible science, but it is not in this mark scheme list.
• Giving only the improvement, e.g. “same distance from lamp”, with no reason.
• Talking about colour again instead of control variables.

✅ Correct answers

After 100 seconds, the temperature difference was 7.5 °C.

The black flask continued to increase for a further 240 seconds.

📐 How to read these values

1. Go to 100 s on the x-axis.
2. Read the black flask temperature and white flask temperature.
3. Subtract: black − white = about 7.5 °C.
4. Find when the white flask stops rising (about 160 s).
5. Find when the black flask stops rising (about 400 s).
6. Calculate further time: 400 − 160 = 240 s.

🧠 Exam technique

• Use the graph carefully; these questions test reading scales accurately.
• If the graph gives a value between lines, estimate sensibly.
• For “a further ... seconds”, subtract the two times, not the temperatures.

❌ Common errors

• Writing 400 s instead of 240 s because you forgot “further”.
• Mixing up temperature difference with time difference.
• Reading from the wrong curve.

✅ Correct answer

The black flask line has a greater gradient (it is steeper), so its temperature increased more in the same time.

💡 Key knowledge

A steeper line on a graph means a faster rate of change. Here, that means the black flask’s temperature rises faster, showing a greater initial rate of absorption of infrared energy.

❌ Common errors

• Saying only “the black flask got hotter” is too vague.
• Talking about the final temperature instead of the initial rate.
• Not referring to the graph shape/gradient.

✅ Correct answer points

• The flasks absorb infrared radiation and transfer energy to the surroundings as well.
• At first, the rate of absorption of infrared is greater than the rate of energy transfer to the surroundings, so temperature increases.
• As the flasks get hotter, the rate of energy transfer to the surroundings increases.
• Eventually, the rate of energy transfer to the surroundings equals the rate of energy transfer to the flask, so the temperature becomes constant.

🧠 Model 4-mark answer

The flasks absorb infrared radiation from the lamp. At first, they absorb energy faster than they transfer energy to the surroundings, so the water temperature rises. As the flasks become hotter, they transfer energy to the surroundings more quickly. Eventually, the rate of energy transfer to the surroundings becomes equal to the rate of energy absorbed, so the temperature stays constant.

💡 Key knowledge

• Infrared radiation transfers energy.
• Objects also lose energy to the surroundings by heating them and by emitting infrared.
• Constant temperature does not mean no energy transfer; it means the transfers are balanced.

❌ Common errors

• Saying “the flask stopped absorbing infrared” once the line becomes flat. It did not necessarily stop; the rates became equal.
• Saying “it reached maximum temperature” without explaining the energy balance.
• Forgetting to mention the surroundings.
• Writing only that it “got hotter because of the lamp” with no explanation of why it later became constant.

🧠 What stronger answers did well

• Used the language of fair testing: same distance, same size/shape, same volume.
• Read graph values carefully and used subtraction where needed.
• Used gradient to compare rates.
• Explained the plateau using equal rates of energy transfer.

❌ Where students lost marks

• Not pairing an improvement with a reason in 05.1.
• Reading the graph too roughly.
• Confusing “steeper graph” with “higher final temperature”.
• Missing the idea that as temperature rises, energy loss to the surroundings also rises.