A student investigates how the resistance of a thermistor changes with temperature. The student records the current in the thermistor at various temperatures, keeping the potential difference across it constant.
Table 9.1
| Temperature of thermistor / ∘C^{\circ}\text{C}∘C | 20 | 30 | 40 | 50 | 60 | 70 |
|---|---|---|---|---|---|---|
| Current in thermistor / mA\text{mA}mA | 1.2 | 2.5 | 5.0 | 9.5 | 18.0 | 32.0 |
The potential difference (p.d.) across the thermistor is 8.0 V8.0\text{ V}8.0 V at 40 ∘C40\ ^{\circ}\text{C}40 ∘C. Calculate the resistance of the thermistor at 40 ∘C40\ ^{\circ}\text{C}40 ∘C. Include the unit.
The student plots the results on a graph of current in thermistor against temperature. The resulting line is a curve that bends upwards, starting from (20 ∘C, 1.2 mA)(20\ ^{\circ}\text{C},\ 1.2\text{ mA})(20 ∘C, 1.2 mA).
The student suggests that the current in the thermistor is directly proportional to its temperature.
Explain how the graph shows that this suggestion is incorrect.
132 exam-style questions on CIE IGCSE Physics 4.2.4a Resistance. Each one has a worked solution and a mark scheme showing where the marks go.