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Practical work is woven right through J249, and although there is no separate practical exam, your practical skills are assessed in the written papers — and they carry serious weight. OCR groups the required practical activities into Practical Activity Groups (PAGs), and the exam can ask about any of them: the apparatus, the method, the variables, the sources of error, and how to improve the results. A student who only "did" the practicals in class without understanding why each step matters will lose marks when the questions probe the technique.
By the end of this lesson you should know the main required practicals across P1–P8, understand how practical skills are examined on paper, and be able to talk confidently about apparatus, variables, accuracy and errors.
At least 15% of the marks across the qualification reward practical skills — planning experiments, choosing apparatus, identifying variables, handling data, and evaluating methods. Because these are tested on paper, the exam cannot watch you use a balance; instead it asks questions like:
So "revising practicals" does not mean re-reading a results table — it means being able to explain and evaluate the method. The most reliable way to prepare is to be able to describe each required practical as if teaching it: what you change, what you measure, what you control, and what could go wrong.
Exam Tip: For every required practical, learn a one-line answer to five questions: What is the independent variable? The dependent? The control variables? The key apparatus? The main source of error? Those five answers cover the overwhelming majority of practical marks.
The table below groups the core J249 practical activities by the physics they investigate. Exact PAG groupings are set by OCR, so check your centre's list — but these are the experiments you should be ready to discuss.
| Area | Required practical | You measure / investigate |
|---|---|---|
| P1 Matter | Density of solids and liquids | Mass (balance) and volume (ruler / displacement) to find ρ=Vm |
| P1 / P7 Energy | Specific heat capacity of a material | Energy supplied vs temperature rise; E=mcΔθ |
| P2 Forces | Force and extension of a spring | How extension varies with force; test F=ke, find the limit of proportionality |
| P3 Electricity | I–V characteristics of components | Current vs potential difference for a resistor, filament lamp and diode |
| P3 Electricity | Resistance of a wire / combinations | How resistance depends on length; series vs parallel |
| P5 Waves | Wave speed in a solid / on water | Frequency and wavelength to find v=fλ (ripple tank, string) |
| P5 Waves | Reflection and refraction / lenses | Ray tracing; angles of incidence and refraction |
| P7 Energy | Thermal insulation | Which material best reduces the rate of energy transfer (cooling curves) |
| P6 Radioactivity | Radiation / absorption (often demonstrated) | How different materials absorb alpha, beta and gamma |
Some of these — particularly anything involving radioactive sources — are usually demonstrated by the teacher rather than done hands-on, but you can still be examined on the method and safety.
Exam Tip: Group the practicals by the equation they test — density practical → ρ=Vm; spring practical → F=ke; wave-speed practical → v=fλ; SHC practical → E=mcΔθ. Linking each experiment to its equation helps you recall both together in the exam.
Practical questions frequently ask about safety and about which apparatus to choose, and both reward specific, reasoned answers rather than generic ones. On safety, the key is to match the precaution to the actual hazard in that experiment. In the specific heat capacity practical, the block and heater become hot, so the relevant precaution is to avoid touching them and to let them cool before handling — not a vague "be careful". In electrical practicals, keeping the current on only briefly stops components overheating (which is both a safety point and a source of error). For any experiment involving radioactive sources, the precautions are specific and examinable: handle sources with tongs to increase distance, point them away from people, minimise the time of exposure, and store them in a lead-lined box. Naming the hazard and the matched precaution is what earns the mark; a generic "wear goggles" scores nothing if goggles are irrelevant to the actual risk.
On apparatus, questions reward choosing an instrument whose resolution suits the measurement. To measure a small extension you want a millimetre ruler (or better) rather than a metre rule read to the nearest centimetre; to measure a short time interval you want a stopwatch or light gates rather than a wall clock; to measure a volume of liquid you want a measuring cylinder rather than a beaker's crude graduations. The reasoning to state is that a higher-resolution instrument reduces the percentage uncertainty in the reading, giving a more accurate result. When a question asks you to "suggest a suitable instrument", it is really testing whether you can match the instrument's resolution to the size of the quantity being measured — a small quantity needs a fine instrument.
Exam Tip: For "name a safety precaution" questions, always state the hazard and the matched precaution together ("the block gets hot, so allow it to cool before handling"). A precaution that does not fit the experiment's actual hazard — like goggles for a purely electrical circuit — earns no credit, however sensible it sounds in general.
Almost every practical question uses this vocabulary, so nail it:
| Term | Meaning | Example (spring practical) |
|---|---|---|
| Independent variable | The one you deliberately change | The force (weight) added |
| Dependent variable | The one you measure in response | The extension of the spring |
| Control variables | Those you keep the same for a fair test | The spring used, temperature |
A "fair test" means only the independent variable changes; everything else is controlled. If more than one thing changes, you cannot tell which caused the effect — a classic evaluation point.
Exam Tip: Remember: you change the independent variable, measure the dependent variable, and keep control variables constant. If a question asks "how would you make this a fair test?", the answer is almost always "control the other variables" — name them specifically.
Practical evaluation questions lean heavily on this set of ideas — they are worth learning as precise definitions:
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