A thermistor is connected in series with a fixed resistor and a battery. Explain what happens to the current through the circuit as the temperature of the thermistor increases.

AQA A-Level Physics (7408) — 3.5.1 Current Electricity · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

As the temperature rises the resistance of the thermistor falls. In a series circuit the total resistance is the sum of the individual resistances, so the overall resistance of the circuit decreases. The battery’s potential difference remains constant. According to Ohm’s law, I = V/R, a lower total resistance gives a higher current. Therefore the current through the circuit increases.

Examiner tips

  • State the temperature‑resistance relationship first, then explain the series‑circuit rule, keep V constant, finish with I=V/R to show the increase.
  • Use the exact terms: resistance, total resistance, series circuit, potential difference, current, Ohm’s law.

Mark scheme (5 marks)

  1. As temperature increases, the resistance of the thermistor decreases
  2. The total resistance of the circuit decreases
  3. Because in a series circuit total resistance is the sum of the individual resistances
  4. The potential difference of the battery stays the same / is constant
  5. So the current through the circuit increases

Key terms in this question

thermistor · series · current

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