A student wants to measure the period of a pendulum accurately. Explain why the student should time several complete oscillations rather than just one, and state how the period is then determined from this measurement.

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)

Timing several oscillations reduces the percentage uncertainty in the measurement. A single oscillation is too short, so any timing error is a large fraction of the time recorded.

The student records the total time for N complete oscillations and then divides this total time by N. The quotient is the period of the pendulum, giving a more reliable and precise value.

Examiner tips

  • Use the word ‘reduce’ to show understanding of uncertainty; mention ‘percentage uncertainty’.
  • Explain that dividing the total time by the number of oscillations gives the period.

Common mistakes

  • Failing to mention the reduction of percentage uncertainty; only stating that more oscillations give a better value.
  • Calculating the period incorrectly, e.g. dividing by 2 instead of the actual number of oscillations.

Mark scheme (4 marks)

  1. Timing several oscillations reduces the percentage uncertainty (in the measurement)
  2. A single oscillation is too short a time interval (making any timing error a large fraction of the measurement)
  3. The total time measured is divided by the number of oscillations
  4. The result gives a more reliable / precise value for the period

Key terms in this question

period · oscillation · pendulum

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