How to Describe Experiments in IGCSE Physics

Describe-an-experiment questions test whether you can plan a fair investigation. The answer must include enough detail for someone to carry out the experiment and obtain valid results.

What to include

1. Equipment list: Name the apparatus. Use correct names (e.g., “newton meter” not “force measurer”).
2. Method: State the steps in order. Include what you measure and how.
3. Variables:
   • Independent variable: what you change
   • Dependent variable: what you measure
   • Control variables: what you keep the same and how
4. Measurements: State the instrument used and how you take the reading (e.g., “read the thermometer at eye level to avoid parallax error”).
5. Repeats: State that you repeat each measurement and calculate a mean to improve reliability.

Example: Investigating how length affects the resistance of a wire

Equipment: Power supply, ammeter, voltmeter, constantan wire, metre ruler, crocodile clips, connecting wires.

Method:

1. Connect the circuit: power supply in series with the ammeter and the wire. Connect the voltmeter in parallel across the wire.
2. Use crocodile clips to connect a measured length of wire (e.g., 20 cm) into the circuit.
3. Switch on and record the ammeter reading (I) and voltmeter reading (V).
4. Calculate resistance using R = V / I.
5. Repeat for lengths 40 cm, 60 cm, 80 cm and 100 cm.
6. For each length, take three readings and calculate the mean resistance.

Control variables: Same wire material (constantan), same wire diameter, same power supply voltage.