All subjects · Physics · WPH13 Practical Skills in Physics I

The Unit 3 practical skills paper and command words

Edexcel IAL Physics · WPH13 Practical Skills in Physics I

Unit 3 is a written paper about practical work. You do not do an experiment in the exam, but you must think like someone who has. This lesson shows what the paper tests and how marks are lost.

Practise this in the app: instant marking and a fix for every mistake. Free, no email needed to start.

Practise this lesson

What the paper is

1 hour 20 minutes, 50 marks, all questions compulsory.
Short-answer, calculation and extended-writing questions, set in the contexts of the AS core practicals (1 to 8) and other AS physics.
At least 20 of the 50 marks are for mathematics at Level 2 or above, so expect calculations, graphs and uncertainties in every question.
Calculators are allowed.

The three skill areas

The specification splits the paper into three kinds of task:

Planning (3.3): you plan an experiment set by Pearson, choosing apparatus, ranges, resolution, control variables, repeats, safety and how to reduce uncertainty.
Implementation and measurements (3.4): you judge an experiment done by an *inexperienced* student: number and range of readings, significant figures, anomalous readings and improvements.
Processing results (3.5): you work with results from a *more experienced* student: calculations, graphs, gradients, units and uncertainties.

Command words

Describe: say what to do or what happens. No reasons needed.
Explain: give a reason for each point (because...).
Calculate / determine: show working and give a unit. Determine often means use the graph.
Show that: every step written out, and the final answer to one more significant figure than the value given.
Deduce / compare: finish with an explicit comparison of two numbers and a conclusion that answers the question.

Examiners repeatedly report that answers lose marks for being generic. 'Repeat and take a mean' gets nothing if the question already says readings were repeated. Make every point specific to the apparatus in front of you.

Quick habits that save marks

Use the names of quantities in methods ('measure the diameter'), not just symbols.
Give units with every measured or calculated value.
Do not round in the middle of a calculation.
Give only as many safety points or reasons as asked for: extra ones are not credited.

Worked example

A cube of side 2.71 cm has a mass of 54.2 g. Show that the density of the material is about 2700 kg m^-3.

Convert to SI units first: side = 0.0271 m, mass = 0.0542 kg.
Volume = 0.0271³ = 1.99 x 10^-5 m³
Density = 0.0542 / (1.99 x 10^-5) = 2723 kg m^-3

Answer: Density = 2720 kg m^-3, given to 3 s.f., one more than the 2 s.f. in 'about 2700'

Key idea: Plan, implement, process. Read the command word, make every point specific to the apparatus, show working, give units, and give 'show that' answers to one more significant figure.

Check yourself

A question asks you to 'show that the speed is about 3 m/s'. How should you give your final answer?
- Written as 3 m/s, the value in the question
- Without working, as the answer is given
- To 1 significant figure, matching the question
- Calculated in full and given to at least 2 significant figures, such as 3.1 m/s
Show answer
Calculated in full and given to at least 2 significant figures, such as 3.1 m/s. In a 'show that' question the answer is already known, so marks are for working and for a final value with more precision than the one given.
What does the command word 'explain' require that 'describe' does not?
- A diagram
- A reason for each point
- A calculation
- A list of apparatus
Show answer
A reason for each point. Explain means give reasons; describe means say what to do or what happens.
In which part of the paper do you judge results collected by an inexperienced student?
- Planning
- Processing results
- Safety only
- Implementation and measurements
Show answer
Implementation and measurements. Specification 3.4: comment on the number and range of readings, significant figures and anomalies.
What is the minimum number of marks on the paper that assess mathematics at Level 2 or above?
- 20 of the 50 marks
- 5 of the 50 marks
- 10 of the 50 marks
- All 50 marks
Show answer
20 of the 50 marks. The specification guarantees at least 20 marks of mathematics.
A question asks you to deduce whether a wire is made of copper. Your calculation is correct. What else is needed for full marks?
- A second calculation using a different method
- A list of other metals
- An explicit comparison of your value with the copper value and a clear conclusion
- A diagram of the wire
Show answer
An explicit comparison of your value with the copper value and a clear conclusion. Examiners often withhold the last mark when the comparison and conclusion are not written out.
A cube of side 1.85 cm has a mass of 49.9 g. Calculate its density in kg m^-3, to 3 s.f., as you would in a 'show that the density is about 8000 kg m^-3' question.
Show answer
7880 kg m^-3. Volume = 0.0185³ = 6.33 x 10^-6 m³; density = 0.0499 / (6.33 x 10^-6) = 7880 kg m^-3.
A question states that readings were repeated and averaged, then asks for another way to improve the accuracy of the timing. Why would 'repeat and take a mean' score nothing?
- Repeating never improves results
- Means cannot be calculated for times
- It repeats what the question already says
- Examiners only accept answers about safety
Show answer
It repeats what the question already says. Examiners do not credit techniques already stated in the question. Give a different, specific technique.

Practise with instant feedback

Sources

Last updated 8 November 2026. Spotted a mistake? Tell us.