A student measures the thickness of a single sheet of paper using a ruler and records a value of 0 mm. Explain why this method is unsuitable and describe a better method the student could use to obtain a reliable measurement of the thickness of one sheet of paper.

Cambridge International IGCSE Physics (0625) — 1.1 Physical quantities and measurement techniques · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

A ruler cannot resolve the small distance of a single sheet of paper – the thickness is far below the 1 mm divisions on the scale.

A better method is to use a micrometer screw gauge to measure the thickness of a stack of many sheets.

Measure the total thickness of, say, 100 sheets with the micrometer.

Divide the total thickness by the number of sheets to obtain the mean thickness of one sheet.

Examiner tips

  • State the limitation of the ruler first. Use the phrase "micrometer screw gauge". Explain the averaging step (total thickness ÷ number of sheets).

Common mistakes

  • Assuming a ruler can read 0 mm; forgetting to mention the micrometer. Using a caliper instead of a micrometer. Failing to divide by the number of sheets to find the mean value.

Mark scheme (4 marks)

  1. A ruler cannot measure such a small distance / the thickness of one sheet of paper is too small to be read on a ruler's scale
  2. Use a micrometer screw gauge (to measure the stack / to measure the thickness)
  3. Measure the thickness of a large number (e.g. many / several / a known number) of sheets of paper together / stack several sheets
  4. Divide the total thickness by the number of sheets to find the thickness of one sheet / calculate a mean value

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