IGCSE Physics Paper 6: why students lose marks on experiments they understand

What Paper 6 actually tests

The syllabus identifies skills ranging from apparatus selection and measurement to interpreting results and evaluating methods. Organise revision by these decisions as well as by apparatus. A question about a spring and a question about a circuit can both test whether you understand the difference between the quantity you change and the quantity you measure.

For each school practical, reconstruct the purpose without looking at the worksheet. State the proposed relationship, sketch the setup and name the readings needed to test it. Then ask what evidence would disagree with your prediction. This turns a remembered procedure into an investigation you can reason about when the question changes the equipment or asks for an unfamiliar extension.

The language rules that earn marks

Name the actual quantity, instrument and action. In a comparison of cooling in different containers, 'keep everything the same' leaves the method ambiguous. Identify relevant controls such as the initial water temperature and water volume, explain how they are set, and state when temperature is measured. Your response must fit the investigation rather than supply a generic list.

When proposing repeats, say what is repeated and how the readings are used. Averaging comparable repeats can reduce the influence of random variation; repeating a ruler reading from the wrong starting point does not remove that offset. If the problem is inconsistent timing, a better timing method may be relevant. If the problem is heat transfer through an uncovered opening, a lid may address it. Link the improvement to the limitation.

Name the practical action and explain why it helps this experiment.

Practise graph technique and interpretation

Label axes with quantities and units, use a suitable scale and plot readings carefully. Draw the line or curve requested by the task. A best-fit line represents the overall pattern; it does not normally mean connecting every experimental point with short straight segments. Investigate an anomalous reading rather than deleting it solely because it makes the graph look untidy.

For an original force–extension example, a best-fit line passes through 0.020 m at 1.0 N and 0.080 m at 4.0 N, with force on the vertical axis. Its gradient is (4.0 − 1.0) / (0.080 − 0.020) = 50 N/m. Reversing the axes changes the gradient and its units. Use separated points on the best-fit line and retain their units through the calculation.

Worked measurement example: separate a reading from a result

A spring has an unloaded length of 12.4 cm and a loaded length of 17.9 cm. Its extension is 17.9 − 12.4 = 5.5 cm, or 0.055 m. The loaded length itself is not the extension. A useful results table keeps the measured length and calculated extension clearly labelled, so another reader can see how the result was obtained.

Now consider how you would make the readings consistently: use the same reference points, align the scale with the length being measured and view a scale appropriately to reduce parallax. If a reading is repeated, return to the same experimental conditions. Do not claim that extra decimal places improve an instrument's resolution or that a mean automatically corrects every weakness in the setup.

Plan an investigation someone else could follow

A useful plan states what changes, how it changes, what is measured, how readings are recorded, which conditions are controlled and how the data answer the question. Include a sensible range and repeated measurements where appropriate to the situation. The exact choices depend on the apparatus and task; avoid inventing a universal number of readings or a procedure that the supplied equipment cannot perform.

For a low-voltage current–voltage investigation, show how the ammeter and voltmeter are connected, explain how the potential difference is varied and identify the paired readings recorded. Consider temperature changes when interpreting the component's resistance. A plan should connect the measurements to the intended graph or calculation, so it is clear how the proposed method can reach a conclusion.

How to prepare in four weeks

If you have four weeks, use the first to diagnose skills with a small selection of questions and your school practical records. In the second, repair measurement, tables and graph work with short tasks. In the third, practise planning and evaluation across fresh contexts. In the fourth, combine those skills under the correct paper conditions and review the remaining gaps. Adapt the sequence if a school assessment or a major weakness changes your priorities.

After marking, write an action that you can test: 'calculate extension before plotting', 'use points on the best-fit line', or 'name the control and how it is maintained'. Then attempt a different question requiring that action. If the mark scheme remains unclear, ask a teacher to explain the physical reason for the criterion. The aim is transferable experimental judgement rather than a memorised collection of phrases.