O-Level Physics Optics Practical Handbook (Paper 3)

2 | Planning framework before you touch the kit

1. Aim: State the physical relationship you will verify (e.g. $1/f = 1/u + 1/v$ for thin lenses).
2. Variables: Identify the independent variable (object distance, angle of incidence, slit spacing) and dependent variable (image distance, angle of refraction, fringe spacing).
3. Controls: Fix light source position, lens height, medium temperature, ripple tank depth, or string tension.
4. Method overview: Describe alignment steps, number of readings, and how you will ensure repeatability.
5. Safety: Mention glare mitigation, handling of glass lenses, water spillage management for ripple tanks.
6. Data treatment: Pre-decide on gradients, reciprocal plots, or trigonometric calculations required by the syllabus (e.g. plotting $1/v$ against $1/u$).

Link each bullet to the P skill descriptors in the SEAB guide so examiners see evidence of syllabus awareness.

3 | MMO drill table for common optics setups

• Record all raw readings with units in a single table; reserve a second column for processed values (e.g. $1/u$, $1/v$, $\sin i$, $\sin r$).
• Note environmental factors (ambient light, draughts affecting ripple tank) because Paper 3 ACE marks reward candidates who comment on such limitations.

4 | PDO: presenting your optics data cleanly

• Tables: Headings should include quantity and unit, e.g. Object distance, u / cm. Maintain consistent significant figures matching measurement precision (ruler: 0.1 cm; protractor: 1°).
• Graphs: Choose axes that linearise the relationship: plot $1/v$ vs $1/u$ for lenses or $\sin i$ vs $\sin r$ for refractive index. Use at least half the grid, draw a best-fit line, and show the large triangle used for gradient calculation.
• Uncertainties: Quote absolute or percentage uncertainty for key readings. When deriving $n$, propagate angle measurement uncertainty $\approx \pm \pu{1^\circ}$ into \(\sin) values.

5 | ACE commentary templates

1. Analysis: Convert raw readings into rates or refractive index, then compare with textbook values (e.g. $n_\text{glass} \approx 1.5$). Highlight percentage difference.
2. Conclusion: State whether results support the theory (“The linear plot of $1/v$ vs $1/u$ yielded $f = 20.1 \pm 0.8 \space \mathrm{cm}$, consistent with the manufacturer’s $\pu{20 cm}$ focal length”).
3. Evaluation: Discuss limitations (e.g. light spread, lens aberration, ripple reflections) and realistic improvements (light shield, black card, deeper water to reduce reflections). Tie recommendations to the skill descriptors in the syllabus.

6 | Quick practice prompts

• Lens drill: Set up three object distances $\pu{30, 40, 50 cm}$ and predict image distances before measuring. Compare predictions to actual readings and comment on discrepancies.
• Refraction analysis: Use simulation data to calculate $n$ and discuss how measurement error in $i$ or $r$ affects the gradient.
• Wave speed task: Collect video of ripple tank waves, measure wavelength across 8–10 crests, and compute speed given frequency. Draft an ACE paragraph discussing systematic errors from reflections.

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Sources

1. SEAB, GCE O-Level Physics Syllabus (6091) 2026

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