How to Answer 'Describe an Experiment' Questions

Use this guide to write clear, complete descriptions of experiments in Cambridge IGCSE Physics 0625 exams.

The five-part framework

1. Apparatus

Name the specific equipment needed. Be precise: “metre ruler” not just “ruler”; “digital balance” not just “scales”; “voltmeter connected in parallel” not just “voltmeter.”

2. Setup

Describe how the apparatus is arranged. A labelled diagram helps here. State what is connected to what and how.

3. Method (step by step)

State the measurements taken in order:

• What you measure.
• What instrument you use to measure it.
• What you vary (independent variable).
• What you keep constant (control variables).

4. Calculations

State the equation you will use to calculate the result. Show how the measurements lead to the answer.

5. Improvements

If asked, state how to improve accuracy or reliability:

• Repeat and average (reduces random error).
• Use a more precise instrument.
• Control temperature or other variables.
• Take multiple readings and plot a graph.

Worked example: “Describe an experiment to measure the density of an irregular solid.” [5 marks]

1. Measure the mass of the object using a digital balance ($m$).
2. Fill a measuring cylinder with water and record the initial volume ($V_1$).
3. Carefully lower the object into the water.
4. Record the new volume ($V_2$).
5. Calculate the volume of the object: $V = V_2 - V_1$.
6. Calculate density: $\rho = m / V$.

Common errors and how to correct them

1. Being too vague. “Measure the length” does not say with what instrument. Write “measure the length using a metre ruler.”

2. Missing the calculation. The experiment is not complete until you state how the measurements produce the answer.

3. Describing a different experiment. Read the question carefully. If it asks for density, do not describe a specific heat capacity experiment.

How to apply this in an exam

Follow the five-part framework. Name the instruments. State what you measure. Write the equation. If the question asks for improvements, give specific actions, not vague intentions.