OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(ii) techniques and procedures used to determine the Young modulus for a…
Full specification wording
Mechanical properties of matter: (ii) techniques and procedures used to determine the Young modulus for a metal
A practical determination of the Young modulus for a metal wire uses a long, thin specimen clamped at one end and loaded at the other over a pulley.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 5 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A practical determination of the Young modulus for a metal wire uses a long, thin specimen clamped at one end and loaded at the other over a pulley. A metre rule or scale measures the original length L between fixed marks, and a micrometer measures the wire diameter d at several places and orientations; the mean diameter gives cross-sectional area A = πd²/4. A mass hanger adds known weights, so force F = mg using g = 9.81 m s⁻². Extension ΔL is measured with a vernier scale or travelling microscope, often against a fiducial mark, after tapping the wire to remove kinks. Plotting F against ΔL gives a straight line through the origin within the elastic limit; its gradient k = F/ΔL, so E = kL/A. Alternatively, E = FL/(AΔL) from a single consistent set of readings.
What earns the marks
- Measures original length L between fixed reference marks with a metre rule, avoiding parallax.
- Measures wire diameter with a micrometer at several positions and orientations, then averages to find A = πd²/4.
- Applies known loads and records extension ΔL using a vernier scale or travelling microscope, tapping the wire to remove kinks.
- Plots a graph of force F against extension ΔL and uses the gradient k with E = kL/A, or substitutes into E = FL/(AΔL).
- Identifies safety and reliability measures such as a safety cushion or G-clamp, eye protection, and keeping stress within the elastic limit.
Common mistakes and how to put them right
Measuring diameter once only.
Put it right: Take repeat readings at different places and orientations and average them.
Using the total length of wire including the clamped portion.
Put it right: Measure only the length between the fixed marks that actually extends.
Ignoring the weight of the hanger or adding masses without converting to force.
Put it right: Compute F = mg for each load.
Plotting extension against force and then using the gradient directly as E.
Put it right: Use the gradient k = F/ΔL in E = kL/A.
Exam tips
- Describe the procedure in a logical sequence: set up, measure L, measure d, load, measure ΔL, analyse.
- State how you reduce uncertainty: repeat diameter readings, use a long wire, use a travelling microscope, tap the wire.
- Show the graph method clearly, labelling axes F and ΔL and explaining that the gradient equals k.
Try the lesson
The start of the Mechanical properties of matter: (ii) techniques and procedures used to determine the Young modulus for a metal lesson, made from checked teaching notes for this specification point.
Listen
A practical determination of the Young modulus for a metal wire uses a long, thin specimen clamped at one end and loaded at the other over a pulley. A metre rule or scale measures the original length L between fixed marks, and a micrometer measures the wire diameter d at several places and orientations; the mean diameter gives cross-sectional area A = πd²/4. A mass hanger adds known weights, so force F = mg using g = 9.81 m s⁻². Extension ΔL is measured with a vernier scale or travelling microscope, often against a fiducial mark, after tapping the wire to remove kinks. Plotting F against ΔL gives a straight line through the origin within the elastic limit; its gradient k = F/ΔL, so E = kL/A. Alternatively, E = FL/(AΔL) from a single consistent set of readings. A strong answer earns marks for these points. Measures original length L between fixed reference marks with a metre rule, avoiding parallax. Measures wire diameter with a micrometer at several positions and orientations, then averages to find A = πd²/4. Applies known loads and records extension ΔL using a vernier scale or travelling microscope, tapping the wire to remove kinks. Plots a graph of force F against extension ΔL and uses the gradient k with E = kL/A, or substitutes into E = FL/(AΔL). A common slip: Measuring diameter once only. Instead, take repeat readings at different places and orientations and average them. Exam tip: Describe the procedure in a logical sequence: set up, measure L, measure d, load, measure ΔL, analyse.
See it
Put it in order
Put these steps in the order they happen.
- 1. Add known weights; force F = mg
- 2. Calculate E = kL/A
- 3. Measure extension ΔL with vernier scale or travelling microscope, tapping wire to remove kinks
- 4. Set up wire clamped at one end, loaded over a pulley
- 5. Measure original length L between fixed marks with a metre rule
- 6. Plot F against ΔL; gradient k = F/ΔL
- 7. Measure diameter d with a micrometer at several places and orientations
- 8. Average diameter to find area A = πd²/4
Key words
Say what each word means before you turn the card.
Uncertainty reduction and repeat readings
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Graphical analysis of Hooke's law data
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Stress, strain and the Young modulus
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See every definition
- Uncertainty reduction and repeat readings
- The mean diameter from readings at several places and orientations gives the cross-sectional area, and the wire is tapped to remove kinks.
- Graphical analysis of Hooke's law data
- Plotting force against extension gives a straight line through the origin within the elastic limit, and its gradient k is used with E = kL/A.
- Stress, strain and the Young modulus
- The Young modulus is found from E = kL/A using the gradient, or from E = FL/(AΔL) from a single consistent set of readings.
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