AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2018: Question 5

✅ Correct answer

The wall has two or three layers. The cavity wall insulation, brick, and block have a low thermal conductivity, so less energy is transferred by conduction.

💡 Key knowledge

• Thermal conductivity tells us how easily energy passes through a material.
• Materials with low thermal conductivity are good insulators.
• A cavity wall has layers and a gap filled with insulation, which slows heat transfer.

🧠 Exam technique

• To get full marks, link the structure of the wall to conduction.
• Use the wording “less energy is transferred” or “rate of energy transfer is lower”.
• Marks are awarded for separate points: structure, property, and effect.

❌ Common errors

• Only saying “it keeps the house warm” is too vague.
• Talking only about convection or radiation is not needed here.
• “Insulation stops heat loss completely” is wrong — it reduces it.

📐 Calculations: step-by-step

1. At 20 minutes, the temperature is 20.8 °C.
2. At 40 minutes, the temperature is 17.4 °C.
3. 30 minutes is halfway between 20 and 40 minutes, so take the midpoint.
4. Calculate the drop: 20.8 - 17.4 = 3.4 °C
5. Half of 3.4 is 1.7 °C
6. Subtract from 20.8: 20.8 - 1.7 = 19.1 °C

Answer: 19.1 °C

✅ Correct answer

Temperature = 19.1 °C

🧠 Exam technique

• This is interpolation — finding a value between two results.
• Use the two nearest values from the table.
• Even if your method is shown, the final answer must be sensible.
• The mark scheme allows answers in the range 18.5–19.1 °C for full marks.

❌ Common errors

• Using the average of all temperatures is not correct.
• Choosing 0 and 120 minutes would make the estimate less accurate.
• Forgetting that 30 minutes is halfway between 20 and 40 minutes.

✅ Correct answer

• The chemical energy store of the fuel decreases.
• The thermal energy store of the water increases.
• The thermal energy store of the air / atmosphere increases.

💡 Key knowledge

• Fuel is burned, so chemical energy is transferred out of the fuel.
• Energy is transferred to the water, heating it up.
• Some energy is also wasted to the surroundings and the air.

🧠 Exam technique

• Use the phrase energy store — this is important in GCSE Physics.
• You do not need long explanations; three clear store changes are enough.
• Marks are usually awarded for each correct store change.

❌ Common errors

• Saying “heat rises” without naming an energy store is too vague.
• Mixing up thermal energy store with temperature.
• Leaving out the air/surroundings loss often loses a mark.

📐 Calculations: step-by-step

1. Write the equation: power = energy transferred ÷ time
2. Convert the energy:
   15 MJ = 15 000 000 J
3. Convert the time:
   10 minutes = 600 s
4. Substitute:
   power = 15 000 000 ÷ 600
5. Calculate:
   power = 25 000 W

Answer: 25 000 W

✅ Correct answer

Power = 25 000 W

🧠 Exam technique

• Always use joules and seconds for power calculations.
• Write the equation before substituting numbers.
• Show unit conversions clearly — they are part of the method marks.
• Answer should be in W, not kW, unless you convert it correctly.

❌ Common errors

• Using 10 instead of 600 seconds loses accuracy and often marks.
• Writing 15 000 000 ÷ 10 is a common trap.
• Forgetting the unit, or giving 25 kW without a correct conversion.

💡 Key facts to remember

• Insulation reduces heat transfer by conduction.
• Estimate values from graphs/tables by interpolation.
• Boilers transfer energy from chemical to thermal stores.
• power = energy ÷ time
• Use J and s in power calculations.

❌ Biggest traps

• Talking about insulation in general terms without conduction.
• Not showing how the 30-minute value is found.
• Forgetting that some energy is transferred to the surroundings.
• Not converting minutes to seconds in the power calculation.