AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2022: Question 4

✅ Correct answer

1 atmosphere = 100 kPa

Accept: 10² kPa

💡 Key knowledge

• 1 atmosphere = 10⁵ Pa
• 1 kPa = 10³ Pa
• So divide by 1000 to change Pa into kPa

🧠 Exam technique

Show the unit conversion clearly if you are unsure. Even though this is only 1 mark, the examiner wants the final unit in kPa.

❌ Common errors

• Writing 1000 kPa instead of 100 kPa
• Forgetting to convert from Pa to kPa
• Leaving the answer in Pa

📐 Calculations

1. Find the range: highest − lowest
2. 0.121 − 0.115 = 0.006 MPa
3. Uncertainty in the mean = half the range
4. 0.006 ÷ 2 = 0.003 MPa
5. Answer: ± 0.003 MPa

✅ Correct answer

Uncertainty = ± 0.003 MPa

Also acceptable in method marks: range = 0.006 MPa, mean = 0.118 MPa.

💡 Key knowledge

• The mean is the average of repeated readings.
• For uncertainty from repeats, GCSE questions usually use half the range.
• Use the same units as the data: here, MPa.

❌ Common errors

• Giving the mean instead of the uncertainty
• Writing 0.118 MPa as the uncertainty — this scores 0 marks
• Using the full range as the uncertainty
• Forgetting the ± sign

✅ Correct answer

The relationship is linear.

💡 Key knowledge

• A linear relationship gives a straight line.
• The gradient is constant.
• This means pressure increases by equal amounts for equal temperature changes.

🧠 Exam technique

Use the word linear or say the gradient is constant. That is exactly what the mark scheme accepts.

❌ Common errors

• Saying directly proportional — not accepted here
• Describing it only as “going up” without naming the type of relationship
• Writing about the graph shape but not the mathematical relationship

✅ Correct answer

As the water starts to boil, more steam particles are produced, so the number of gas particles increases. The particles also gain energy and move faster. They collide with the cooker walls more often, and each collision exerts more force. This makes the pressure increase.

💡 Key knowledge

• Boiling produces more gas particles.
• Higher temperature means higher average kinetic energy.
• Faster particles hit the walls more often.
• Each collision is harder, so pressure rises.

🧠 Exam technique

• Write the explanation as a chain of cause and effect.
• Use particle language: particles, collisions, force, pressure.
• If you miss out one key link, you may lose a mark.

❌ Common errors

• Saying “the particles expand” — particles do not expand
• Talking only about “heat” without linking to particles
• Only saying “there is more steam” with no explanation of why pressure rises
• Not mentioning collisions with the cooker walls

✅ Correct answer

The particles spread out, so the steam takes up a greater volume. Since density = mass ÷ volume, the density decreases.

💡 Key knowledge

• Gas particles are far apart and can move away from each other.
• When gas expands, the same amount of mass occupies a bigger volume.
• If mass stays the same and volume increases, density decreases.

🧠 Exam technique

For 3 marks, make sure you include: particles spread out → volume increases → density decreases.

❌ Common errors

• Saying “particles expand” — this is not correct
• Writing only “density decreases” without explaining why
• Using the wrong formula for density
• Saying the mass increases or decreases without support

💡 Key facts to remember

• 1 atm = 10⁵ Pa = 100 kPa
• Uncertainty from repeats = half the range
• A straight-line graph shows a linear relationship
• Heating a gas increases particle speed and pressure
• Gas pressure comes from particles colliding with the container walls
• Density falls if the same mass spreads into a larger volume

🧠 How to score full marks

• Use the exact command word: calculate, describe, explain.
• For explanation questions, chain your ideas logically.
• Use scientific vocabulary from the particle model.
• Check units carefully: kPa, MPa, °C.