Describe how the resistance of a thermistor changes as its temperature decreases, and explain how this change affects the current through it when it is connected to a fixed potential difference.

AQA GCSE Physics (8463) — 4.2.1 Current, potential difference and resistance · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

The resistance of a thermistor rises as its temperature falls.
The higher resistance means a smaller current for the same applied potential difference.
The applied potential difference is fixed.
Therefore, as the temperature decreases, the current through the thermistor decreases.

Examiner tips

  • Use the term "thermistor" and "resistance" correctly. Show the relationship R↑ → I↓ using Ohm’s law. Mention that the applied voltage is unchanged. Keep the answer concise to fit the 4‑mark limit.

Common mistakes

  • Saying the resistance decreases instead of increases. Confusing the thermistor with a normal resistor. Forgetting that the applied potential difference is fixed.

Mark scheme (4 marks)

  1. The resistance of a thermistor increases as its temperature decreases.
  2. The greater the resistance, the smaller the current for a given potential difference.
  3. The potential difference across the thermistor remains fixed / unchanged.
  4. So as temperature decreases, the current through the thermistor decreases.

Key terms in this question

thermistor · resistance · potential difference · current

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