2, 4–8Working as a PhysicistCore

Planning, Evidence and Scientific Decisions

Edexcel practical assessment connects experimental planning, trustworthy evidence and clear scientific communication. Build investigations around testable models, and evaluate claims through their methods, uncertainties and consequences.

40 min 1.2 Measurement and Uncertainty

What you'll be able to do

Plan controls, ranges and measurement methods
Explain repeat readings and pilot trials
Distinguish written assessment from practical endorsement
Evaluate scientific claims, risks and benefits

Start with a relationship and an observable

State the independent variable you will change and the dependent quantity you will measure. Identify controls by explaining how each could affect the result. A hypothesis should predict a relationship, not merely say that something “changes”. Choose a range wide enough to test it and an interval small enough to show the trend.

Translate the model into an expected graph and gradient before collecting data. For example, testing pendulum T² against length makes the gradient 4π²/g. That tells you which quantities need accurate measurement and why timing several cycles is helpful.

A method that another student could follow

Specify the apparatus, its arrangement, a consistent reference point and the sequence of readings. Use a pilot trial to choose suitable ranges, avoid saturation and estimate the dominant uncertainty. Repeat independent measurements where they assess random variation; keep raw data and units rather than only a final average.

Identify concrete hazards, who could be harmed and the controls used in the centre’s approved procedure. A vague instruction to “be careful” does not address a hot wire, falling load or laser beam. Explain checks for zero error, calibration drift and control-variable stability.

Edexcel practical assessment and evidence

Written examinations assess experimental planning, data analysis and evaluation, including the 16 specified core practicals. The separate Science Practical Endorsement depends on teacher-assessed evidence of competence against the Common Practical Assessment Criteria; reading notes or passing a quiz cannot award it.

Maintain a contemporaneous record of the actual method, raw readings, analysis, changes and evaluation. Pearson’s 16 core practicals organise practical learning across the course. They are not AQA’s list of 12, and a generic experiment with similar equipment may test a different relationship. Use the numbered practical lessons alongside the centre’s approved laboratory procedures.

How scientific claims are checked and used

A scientific argument connects a claim to evidence and a physical model, states assumptions and accounts for uncertainty. Independent replication tests whether a result depends on one apparatus or team. Peer review can challenge methods and interpretation before publication, but neither peer review nor one replication guarantees that a claim is permanently correct. Reporting negative results, conflicts of interest and accessible methods helps other scientists judge reliability.

When science informs a decision, distinguish measured evidence from value judgements. Compare expected benefits, the probability and severity of possible harms, available alternatives and who bears the costs. A small relative risk increase may correspond to a small absolute change when the baseline is low. Communicate units, conditions and uncertainty for the intended audience rather than presenting extra decimal places as proof of certainty.

Work through the reasoning

Try each problem before opening the worked solution. State the physical model, show substitutions with consistent units, and explain what your answer means.

Example 1Design a timing improvement for a pendulum with period about 1 s when stopwatch uncertainty is ±0.2 s.

1One-cycle timing has about 20% uncertainty.

2Timing 20 complete cycles gives about 20 s and 1% timing uncertainty for the same absolute interval uncertainty.

3Repeat and average independent timings while keeping amplitude small.

AnswerTime many complete cycles and divide; explain the reduced fractional uncertainty.

Example 2A student wants to test resistance against wire length but current rises as the wire is shortened. Identify a risk to the model and a control.

1Greater current can heat the wire.

2Resistivity then changes, so the relationship no longer varies length alone.

3Use a suitably low controlled current, switch off between readings and monitor for drift.

AnswerControl heating and justify it through the temperature dependence of resistance.

Common mistakes to avoid

Saying “repeat to remove systematic error”.

Repetition addresses random variation; calibration or method changes address systematic effects.

Writing a safety control with no named hazard.

Link a concrete hazard to an effective procedure or protection.

Key takeaways

Plan measurements around a physical relationship.
Pilot trials and explicit controls improve experimental design.
Written practical skills and the teacher-assessed endorsement are distinct.

Test yourself

Answer a few questions, then review anything you missed.

Next step

Keep practising

Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.

Browse practice topics

Related lessons

All 5 lessons