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Measuring motion without hiding uncertainty Small length errors can matter greatly in density Sample stiffness and Young modulus describe different things Stress and pressure share units, but describe different loading Measuring Young modulus accurately Why wire diameter matters in resistivity A Planck-constant experiment needs uncertainty analysis Instrument choice sets the measurement limits Materials3.4 Implementing1.1.2 Measurements and uncertainty2.2.1 Kinematics3.1.1 Density and pressure3.2.4 Springs3.4.1 Mechanical properties of matter3.4.2 Resistivity4.2.4 Photons4.5.1
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Measuring Young modulus accurately

OCR A AS Physics · Two ideas, one explanation

A thin wire’s diameter is measured to calculate its cross-sectional area. The squared diameter makes this measurement especially important in a Young-modulus calculation.

E = FL/(Ax) A = πd²/4

Follow the reasoning

  1. Measure diameter at several positions and orientations.
  2. Measure extension from the original length, correcting any zero offset.
  3. Combine uncertainties with the correct powers.
Specification outcomes (4)
  • 3.4.2(d)(i) Define Young modulus, E = stress / strain.
  • 3.4.2(d)(ii) Use techniques and procedures to determine the Young modulus for a metal.
  • 2.2.1(a) Understand systematic errors (including zero errors) and random errors in measurements.
  • 2.2.1(c) Calculate absolute and percentage uncertainties when data are combined by addition, subtraction, multiplication, division or raising to powers.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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