Resistance and temperature

curriculum-key-fact
The resistance of a metal conductor is due to collisions between the free electrons of the electric current and the metal ions of the wire.
The resistance of a metal conductor is due to collisions between the free electrons of the electric current and the metal ions of the wire.

If the temperature of a metal conductor increases, the ions of the metal vibrate more vigorously.

This increases the number of collisions between the free electrons and the ions.

Hence, for a metal, resistance increases with increasing temperature.

Often the increase in temperature is caused by an increase in current.

An example is a filament lamp.

As current increases, the filament gets hotter and the resistance of the bulb increases.

As current increases, the filament gets hotter and the resistance of the bulb increases.

A thermistor is a device that’s resistance changes with temperature.

The resistance of an NTC thermistor decreases with increasing temperature.

A voltage-current graph for a thermistor is shown below.

A voltage-current graph for a thermistor

Voltage - Current graph for a thermistor as current and temperature rise.