EFFECT OF TEMPERATURE ON RESISTANCE

The electrical resistance generally changes with the change of temperature. The resistance does not only increase with the rise in temperature but it also decreases in some cases. In fact, the increase or decrease in resistance with the rise in temperature depends on the nature of the resistance material discussed as follows:

1. Pure metals: When the resistance is made of some pure metal (copper, aluminium, silver, etc.), its resistance increases with the increase in temperature. The increase is large and fairly uniform for normal range of temperature, and therefore, temperature–resistance graph is a straight line. Thus, pure metals have positive temperature coefficient of resistance.
2. Alloys: When the resistance is made of some alloy (e.g., Eureka, Manganin, Constantan, etc.), its resistance increases with the increase in temperature. But the increase is very small and irregular. In the case of above-mentioned alloys, the increase in resistance is almost negligible over a considerable range of temperature.
3. Semiconductors, insulators, and electrolytes: The resistance of semiconductors, insulators, and electrolytes (silicon, glass, varnish, etc.) decreases with the increase in temperature. The decrease is non-uniform. Thus, these materials have negative temperature co-efficient of resistance.