AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2021: Question 4

✅ Correct answer

Zero error

Mark scheme also allows systematic error.

💡 Key knowledge

• A balance should read 0.0 g when nothing is on it.
• If it shows 4.2 g with no mass, the scale is offset.
• This means every mass measured will be wrong by the same amount unless corrected.

🧠 Exam technique

• For a single mark, use the exact phrase zero error.
• If you write systematic error, that is also accepted here.
• Do not describe the reading as “wrong” only — name the type of error.

❌ Common errors

• Saying random error — this is not correct because the balance is consistently offset.
• Saying parallax error — this is about reading scales, not balances.
• Saying calibration error without explaining the zero offset may be too vague.

✅ Correct answer

Reset the balance to zero g.

Also accepted: subtract the reading shown on the balance from the reading taken.

💡 Key knowledge

• If the balance shows 4.2 g before the cube is added, that is the zero error.
• The student must tare the balance or correct for the offset.
• This removes the effect of the faulty starting point.

🧠 Exam technique

• Use a practical action: reset to zero, tare, or subtract the offset.
• One mark questions need a direct fix, not a long explanation.

❌ Common errors

• “Read it again” — this does not fix the zero error.
• “Use a different balance” — possible, but not the best mark-scheme response.
• Forgetting to mention the value should be corrected to 0 g.

✅ Correct answer

Resolution

💡 Key knowledge

• Resolution means the smallest change an instrument can measure.
• The Vernier callipers gave 20.1 mm while the micrometer gave 20.14 mm .
• The micrometer has a smaller step size, so it has a higher resolution.

🧠 Exam technique

• When comparing instruments, focus on the measurement detail.
• The mark scheme wants the word resolution exactly.

❌ Common errors

• Saying accuracy — this is related but not the mark-scheme word here.
• Saying precision — plausible, but not the expected answer for this mark.

✅ Correct answers

• Place the measuring cylinder on a horizontal surface.
• View with your eye in line with the level of the water.

Also accepted: read from the bottom of the meniscus.

💡 Key knowledge

• A tilted cylinder can give a misleading volume.
• Looking from above or below causes parallax error.
• Liquids in a measuring cylinder are read at the bottom of the meniscus.

🧠 Exam technique

• For 2 marks, give two separate improvements.
• Each point must be clear and practical.

❌ Common errors

• “Use a bigger cylinder” — not the accepted accuracy improvement here.
• “Hold it steadier” — too vague.
• “Look carefully” — not specific enough for a mark.

✅ Correct answer

1. Add several coins to the measuring cylinder.
2. Measure the change in water level.
3. Divide by the number of coins added.

The mark scheme allows a minimum of 5 coins if a number is given.

💡 Key knowledge

• One coin may produce too small a change to read accurately.
• Using several coins makes the volume change larger and easier to measure.
• Then divide to find the volume of one coin.

🧠 Exam technique

• Use the chain: add many coins → measure total displacement → divide by number of coins.
• This is a classic accuracy answer: increase the measured change to reduce percentage uncertainty.

❌ Common errors

• Measuring one coin only — too little displacement.
• Forgetting to divide by the number of coins.
• Not using the change in level, only the final level.

📐 Calculations — step by step

1. Use the old penny data to find the cross-sectional area:
   volume = mass ÷ density
   volume = 3.6 ÷ 8.9 = 0.404... cm³
2. Use volume = area × thickness :
   area = volume ÷ thickness = 0.404... ÷ 0.16 = 2.53 cm²
3. Find the new coin volume:
   volume = area × thickness = 2.53 × 0.17 = 0.4301 cm³
4. Calculate density of the new penny:
   density = mass ÷ volume = 3.6 ÷ 0.4301 = 8.37... g/cm³
5. Round to 2 significant figures:
   8.4 g/cm³

✅ Final answer

X = 8.4 g/cm³

The mark scheme allows working through 8.37... and then rounding correctly to 8.4 g/cm³.

💡 Key knowledge

• Density = mass ÷ volume
• Volume of a disc = cross-sectional area × thickness
• Use consistent units: mass in g, volume in cm³, density in g/cm³.

🧠 Exam technique

• Show all working to gain method marks.
• Keep track of which disc you are using for the area and which for the final density.
• Give the final answer to 2 significant figures only.
• Units are essential: missing g/cm³ can lose the final mark.

❌ Common errors and traps

• Using the wrong thickness with the wrong disc.
• Dividing by thickness in the wrong place.
• Forgetting to calculate area first from the old penny data.
• Giving the final answer as 8.37 instead of rounding to 8.4.
• Writing the unit as g/mm³ or leaving units off.

💡 Mark breakdown

• 04.1 — 1 mark: identify the error type.
• 04.2 — 1 mark: state how to correct the balance.
• 04.3 — 1 mark: name the instrument property resolution.
• 04.4 — 2 marks: give two clear ways to improve accuracy.
• 04.5 — 3 marks: describe the displacement method in a correct sequence.
• 04.6 — 5 marks: method plus final rounded density.

🧠 What top-level answers did well

• Used exact scientific vocabulary: zero error, resolution, horizontal surface.
• Gave practical, exam-ready steps rather than vague descriptions.
• Showed clear calculation steps and used the correct units.
• Rounded correctly to the required number of significant figures.