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AQA · GCSE · Combined Science · Higher

Uncertainty from repeated pressure readings

Q04.2 2 marks

A student investigated how the pressure of a gas depends on its temperature. The volume of the gas did not change.

The student took four pressure readings for each temperature.

Table 1 shows the pressure readings when the temperature was 50.0 °C

Calculate the uncertainty in the mean pressure.

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Marking points

  1. 1 Find the range of the pressure readings: 0.121−0.115=0.006 MPa0.121-0.115=0.006\ \mathrm{MPa}.
  2. 2 Use half the range to give the uncertainty: ±0.003 MPa\pm0.003\ \mathrm{MPa}.

Full-mark answer

The range is 0.121−0.115=0.006 MPa0.121-0.115=0.006\ \mathrm{MPa}. The uncertainty in the mean is half the range, so the uncertainty is ±0.003 MPa\pm0.003\ \mathrm{MPa}.

Why this answer loses marks

±0.006 MPa\pm0.006\ \mathrm{MPa}

This gives the full range rather than half the range.

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