A student uses a micrometer screw gauge rather than a ruler to measure the diameter of a thin copper wire. Explain why the micrometer screw gauge is more suitable for this measurement, and state one advantage of using a digital device rather than an analogue device when taking this reading.

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)

The wire’s diameter is very small, so a ruler would give an inaccurate reading.
A micrometer screw gauge can measure to 0.01 mm, allowing the small distance to be measured accurately.
A digital device displays the measurement directly on a screen, so there is no scale to read.
Using a digital device removes the risk of parallax or human reading error.

Examiner tips

  • Use the word ‘accurately’ to show understanding of precision. Mention the 0.01 mm resolution to hit the point on the scheme. State the digital advantage as ‘direct display’ and ‘no parallax’ to cover both marks.

Common mistakes

  • Claiming a ruler is more accurate for small diameters. Forgetting to mention the 0.01 mm resolution. Saying the digital device is ‘more accurate’ without explaining the reason.

Mark scheme (4 marks)

  1. The wire's diameter is very small / too small to measure accurately with a ruler
  2. The micrometer screw gauge can measure to 0.01 mm / measures very small distances accurately
  3. A digital device displays the measurement directly on a display (no scale to read)
  4. Using a digital device reduces / removes the risk of parallax error / human reading error

Key terms in this question

micrometer screw gauge · analogue device · digital device

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