Young's Modulus at Home: Building a Searle Rig That Meets H2 Physics Standards

TL;DR
Two retort stands, a precision micrometer, and a DSLR or smartphone for extension tracking are enough to recreate Searle’s apparatus at home.
Systematic alignment, load incrementation in 1 N steps, and gradient calculations from \Delta L–force graphs keep you within 5 % of handbook Young’s modulus values.
The activity rehearses every Paper 4 bullet: calibration, safety, linearisation, and uncertainty commentary.

Why Young's Modulus Still Matters in 2026 Practical Papers

• SEAB 9478 emphasises mechanical properties under the “Materials” outcome; examiner reports continue to flag poor handling of stress–strain graphs.
• Universities look for candidates who can translate Hooke’s law into elastic modulus discussions during entrance interviews.
• Tuition centres with tensile rigs differentiate themselves — but you can replicate the rig with S$150 of equipment for your home lab.

Apparatus Checklist

Build and Calibration Workflow

1. Prepare twin wires. One carries the load, the other acts as compensating wire linked to the vernier reference. Equal length and clamping height reduce torsion.
2. Zero the vernier. Adjust the jockey weight so the index aligns with zero at rest. Document any residual offset as a systematic uncertainty.
3. Measure diameter along three points separated by 120° rotations. Average and note the micrometer’s least count in your logbook.
4. Level the pointer mirror using a spirit level. This cuts down parallax when reading extensions visually or from still images.

Data Collection and Processing

1. Load the wire in 1 N steps, waiting 30 s between additions to minimise creep.
2. Record extension using live vernier readings or by annotating still frames in Tracker / Vernier Graphical Analysis.
3. Plot extension \Delta L against force F; the slope yields \frac{L}{AY}. Rearrange to compute Young’s modulus Y = \frac{FL}{A\Delta L}.
4. Propagate uncertainties: include diameter measurement error (dominant via cross-sectional area) and reading precision (±0.1 mm on vernier).
5. Compare the experimental Y with data book values (e.g. nichrome 1.6\times 10^{11}\text{ Pa}). Comment on percentage difference and likely causes.

Safety and Risk Controls

• Always wear safety goggles — fine wires snap dramatically when loaded near their elastic limit.
• Enclose masses in a plastic tray to avoid foot injuries if the hanger drops.
• Warn students about stored elastic energy; unload gradually rather than removing the entire stack at once.

Extension Ideas for High-Achievers

• Replace manual readings with a USB displacement sensor (Vernier LDV) and compare analogue vs digital uncertainties.
• Investigate hysteresis by unloading in steps and plotting the return curve.
• Swap in polymer fishing line to discuss non-linear elasticity and time-dependent creep, referencing IB/SEAB comparative questions.
• Link the experiment to Setting up a Physics Lab at Home to turn this into a module within your 12-week practical sprint.

References

• Khan Academy, Young’s modulus (modulus of elasticity)
• Encyclopædia Britannica, Young’s modulus
• Singapore Examinations and Assessment Board, GCE A-Level Examinations practical requirements