A student is investigating whether the colour of a surface affects how quickly it cools. The student heats identical metal cans, one painted matt black and one left shiny and unpainted, to the same starting temperature. Explain how the student should carry out a fair test and why controlling variables is important in this investigation.

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).

A student wants to find out if the colour of a metal surface affects the rate at which it loses heat to the surroundings. They have two identical metal cans, a thermometer, a stopwatch, and access to hot water.

Model answer (4 marks)

1. Use identical cans, same volume of water and same initial temperature for both.
2. Place the cans in the same room, at the same distance from any heat source or draft.
3. Record the temperature at the same time intervals for each can, using the same thermometer and stopwatch.
4. Repeat the experiment several times for each can and calculate the mean temperature at each interval, discarding any anomalous readings after checking for errors.

Examiner tips

  • Use numbered points to show each controlled variable. Mention that only colour changes. Show repeat trials and mean calculation. Explain why outliers are excluded.

Common mistakes

  • Changing the volume of water or initial temperature. Not using the same room conditions. Failing to repeat trials or calculate a mean. Ignoring anomalous data instead of checking it.

Mark scheme (4 marks)

  1. The student must keep all variables the same except for the colour/surface of the can (e.g. same volume of water, same starting temperature, same room conditions, same time intervals)
  2. Controlling variables ensures any difference in cooling rate is due to the surface colour and not another factor / makes it a fair test
  3. The student should take repeat measurements / repeat the experiment for each can and calculate a mean temperature reading at each time interval
  4. The student should identify and deal with anomalous results / outliers by checking and, if confirmed anomalous, excluding them from the mean

Key terms in this question

fair test · variable

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