All subjects · Physics · WPH13 Practical Skills in Physics I

Writing a plan: extended-response questions

Edexcel IAL Physics · WPH13 Practical Skills in Physics I

Specification 3.3 asks you to plan an experiment set by Pearson. These answers are worth several marks and reward a clear, complete structure.

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

Practise this lesson

A checklist for any plan

1. Measurements: list every quantity to measure and the instrument for each, with its resolution where it matters.

2. Technique: how to make each measurement accurately (set square, eye level, many oscillations, micrometer at several places, zero error).

3. Independent variable: how it is changed, the range and number of values (at least six).

4. Control variables: what is kept constant and how.

5. Repeats: repeat each reading and find the mean.

6. Analysis: which graph, what its gradient or intercept equals, how the final result is calculated.

7. Uncertainty: the main source and how it is reduced.

8. Safety: a specific hazard and precaution, if asked.

Writing style

Example outline

Plan to find the spring constant k of a spring from oscillations, using T = 2π sqrt(m/k):

Worked example

In the spring plan, the graph of T2 against m has gradient 0.158 s2/kg. Find k.

  1. T2 = (4π2/k) m, so gradient = 4π2/k
  2. k = 4π2 / 0.158 = 249.9 N/m

Answer: k = 250 N/m

Key idea: List measurements and instruments, techniques, the range and number of values, controls (and how), repeats, the graph and what its gradient gives, the main uncertainty, and a specific safety point.

Check yourself

  1. A graph of T2 against m for a mass-spring system has gradient 0.098 s2/kg. Find k in N/m, to 3 s.f.
    Show answer

    403 N/m. k = 4π2 / 0.098 = 403 N/m.

  2. For T = 2π sqrt(m/k), which graph gives k most directly from its gradient?
    • T2 against m
    • T against m
    • T against m2
    • m against T
    Show answer

    T2 against m. T2 = (4π2/k) m is a straight line through the origin.

  3. Which statement about the independent variable would earn credit in a plan?
    • Use a range of masses
    • Use lots of different masses
    • Use six masses from 100 g to 600 g in 100 g steps
    • Use masses that seem sensible
    Show answer

    Use six masses from 100 g to 600 g in 100 g steps. A number of values and a range are both stated.

  4. In the spring plan, name one control variable and say how it is kept constant.
    Show answer

    Use the same spring throughout; or keep the amplitude small and the same each time by displacing the mass by the same small distance.. Name the variable and the way it is controlled.

  5. Which sentence is written in the style examiners prefer for a method?
    • Find T using t/20
    • Do 20T
    • Measure t, then T
    • Measure the time for 20 oscillations with a stopwatch and divide by 20
    Show answer

    Measure the time for 20 oscillations with a stopwatch and divide by 20. Methods should use names of quantities and instruments, not bare symbols.

  6. A plan to find k from T2 against m includes measuring the length of the spring for each mass. Why is this a weakness?
    • It makes the experiment dangerous
    • It is not needed for the analysis, so it wastes time
    • It changes the spring constant
    • It adds a systematic error
    Show answer

    It is not needed for the analysis, so it wastes time. Only quantities in the analysis need measuring.

Practise with instant feedback

Sources

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