Edexcel A-Level Physics Stress, Strain and Young Modulus

Practise Edexcel A-Level Physics stress, strain and Young modulus through wire-extension data, stress-strain gradients, breaking stress and safety checks.

Exam points

calculate stress, strain or Young modulus from force, area, extension and length
use load-extension or stress-strain graph gradients to determine Young modulus
compare calculated stress with breaking or yield stress to judge safety or support

[Maximum number: 3]

A student carried out an experiment to determine the Young modulus of a sample of stainless steel in the form of a wire. The student added weights to the wire and measured the corresponding extensions.

The wire had an unstretched length of 2.6 m . The diameter of the wire was $5.6 \times 10^{-4} \mathrm{~m}$ .
The student plotted a graph of weight against extension. The graph showed that the limit of proportionality was not exceeded.

The student's graph is shown below.

Weight / N

Figure for Question 1.4.28 - Stress, strain and Young modulus question 1 — Edexcel A-Level Physics AS

Determine the Young modulus of stainless steel using your value for the gradient.
(3)

Young modulus =

Rearranges E= stress / strain to get E= gradient $\times_{\bar{A}}^{x}$

Or Rearranges E = stress / strain to get gradient $=\frac{A_{A}^{A} E}{x}$

Use of $A=\pi r^{2}$

Young modulus $=2 \times 10^{11} \mathrm{~Pa}$

(allow ecf from (b)(i))

Example of calculation

$A=\pi \times\left(2.8 \times 10^{-4}\right)^{2}=2.46 \times 10^{-7} \mathrm{~m}^{2}$ $E=1.85 \times 10^{4} \mathrm{~N} \mathrm{~m}^{-1} \times 2.6 \mathrm{~m} \div 2.46 \times 10^{-7} \mathrm{~m}^{2}=1.95 \times 10^{11} \mathrm{~Pa}$

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1.4.28 - Stress, strain and Young modulus question 1