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A2 Daily A Level Physics question

2026-04-02 OCR A Uncertainty propagation (no calculus) Module 2.2.1 — Making measurements and analysing data: uncertainties (absolute/percentage) and propagation for products/quotients and powers Module 6.1.1 — Practical skills assessed in a written examination: processing data and evaluating uncertainty

A student determines g using a simple pendulum, using the proportionality g ∝ L/T^2. The length L has a percentage uncertainty of 1.0% and the measured period T has a percentage uncertainty of 2.0%. Using appropriate propagation rules, estimate the percentage uncertainty in g.

  1. A 5.0% (correct)
  2. B 3.0%
  3. C 1.0%
  4. D 2.0%

Answer

The correct answer is A.

Correct: A — 5.0%. For products/quotients, percentage uncertainties add, and a squared term contributes twice its percentage: 1.0% + 2×2.0% = 5.0%. A applies the correct percentage-adding rule with the power on T. B (3.0%) just adds 1.0% and 2.0%, ignoring that T is squared. C (1.0%) wrongly assumes only L contributes and neglects T’s uncertainty. D (2.0%) takes only the largest single uncertainty instead of combining contributions and also ignores the square on T.

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