Resistance-temperature graphs have distinct shapes for metals, thermistors, and superconductors

Resistivity & Superconductivity — AQA A-Level Physics

Metal

Straight line with a positive gradient.
ResistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohms (Ω). increases roughly linearly with temperature.
Does not reach zero at 0 K (there is always some residual resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to current. Measured in ohms (Ω). from impurities).

NTC Thermistor

Steep exponential-type decay curve.
Very high resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). at low temperature, falling rapidly and then levelling off.
The rate of change is much greater than for metals.

Superconductor

Follows the normal metal curve down to T_c.
At T_c, the resistance drops abruptly and discontinuously to exactly zero.
Below T_c, the resistance remains at zero.

Three resistance-temperature graphs side by side. (1) Metal: positive linear slope. (2) NTC thermistor: steep decay curve. (3) Superconductor: follows metal curve then drops vertically to zero at T_c.

Examiner Tips and Tricks

You may be asked to sketch any of these three graphs.
Label axes (resistance/Ω on y-axis, temperature/K or °C on x-axis), mark key features (gradient direction, T_c), and annotate the physical reason for each shape.