A student is investigating how the mass of sugar dissolved in water affects the time taken for the solution to reach a certain temperature when heated. The student plans to repeat each measurement three times and calculate a mean. Explain why repeating measurements and calculating a mean improves the quality of the results.

OCR GCSE Physics A: Gateway Science (J249) — P9 Practical skills · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Repeating measurements allows anomalous results or outliers to be identified.
Anomalous results can be discarded or not included in the mean.
Calculating a mean reduces the effect of random errors.
This makes the result more reliable and increases reliability.

Examiner tips

  • Use the exact wording from the mark scheme – e.g. ‘identifying anomalous results’ and ‘reduces the effect of random errors’.
  • Show the logical sequence: repeat → identify outliers → calculate mean → improve reliability.
  • Keep each point concise – 1–2 sentences per point.

Common mistakes

  • Using vague terms such as ‘more accurate’ instead of ‘more reliable’.
  • Failing to mention both identification of outliers and reduction of random error.
  • Writing a single long paragraph instead of separate points.

Mark scheme (4 marks)

  1. Repeating measurements allows anomalous results / outliers to be identified
  2. Anomalous results can be discarded / not included in the mean
  3. Calculating a mean reduces the effect of random errors
  4. This makes the result more reliable / increases reliability

Key terms in this question

mean

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