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A2 Daily A Level Physics question

2026-05-25 OCR A Materials: practical methods (Young modulus) OCR-A Module 3.4 Materials — stress–strain behaviour; Young modulus determination (qualitative/practical) OCR-A Module 1.2 Practical skills — improving precision and reducing uncertainties

In a lab to determine the Young modulus of a metal wire by adding masses and measuring its extension, you want to reduce the percentage uncertainty in the extension reading without changing the measuring scale or the mass steps. Which change to the setup is best?

  1. A Use a shorter, thicker steel wire so it stays stiff and the extension is small.
  2. B Replace the steel wire with a rubber cord so the extension is much larger for the same mass.
  3. C Use a longer, thinner steel wire so the extension for each added mass is larger and easier to read. (correct)
  4. D Hang two identical steel wires in parallel to share the load, reducing the strain on each.

Answer

The correct answer is C.

Correct: C — Use a longer, thinner steel wire so the extension for each added mass is larger and easier to read. A Short and thick reduces extension for a given load, making percentage uncertainty in the reading larger. B Rubber is not reliably linear in this context and shows hysteresis, so a big stretch does not give a valid modulus. C Longer length and smaller cross-sectional area increase extension for the same load, improving resolution without changing the instrument. D Two wires in parallel share the load and reduce extension, which worsens percentage uncertainty.