Resistance of a wire — required practical

AQA GCSE Physics

Investigate how the length of a wire affects its resistance.

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Method

  1. Set up a circuit with the wire, an ammeter (in series) and a voltmeter (across the wire).
  2. For each length, measure the current and potential difference and calculate resistance R = V ÷ I.
  3. Repeat for a range of lengths (e.g. 10–100 cm).

Variables

  • Independent variable: Length of the wire
  • Dependent variable: Resistance (calculated from V ÷ I)
  • Control variables: Material and cross-sectional area of wire, temperature

Results & analysis

Resistance is directly proportional to length — a graph of resistance against length is a straight line through the origin. Doubling the length doubles the resistance.

Risk assessment

  • The wire can get hot — switch off between readings to avoid heating (which would change resistance).

Improving accuracy & reliability

  • Take readings quickly / switch off between them so the wire does not heat up.
  • Repeat and take a mean.
Exam tip: Temperature must be controlled — a hot wire has a higher resistance, so keep the current low and switch off between readings.

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