The effect of rise of temperature on electrical resistance is not always an increase in resistance but sometimes there is a decrease in resistance also.
The effect of temperature on different types of materials can be classified as follows:
(i) Pure Metals: With a rise in temperature, the resistance of pure metals increases and ∝, the temperature coefficient of resistance is said to be positive.
(ii) Insulators, Electrolytes, etc: In the case of insulators, semi-conductors and electrolytes the electrical resistance decreases with a rise in temperature and ∝ in such cases is said to be negative.
(iii) Alloys: The resistivity of an alloy is usually considerably greater than that of its constitute metals and its ∝ is ordinarily very small and irregular. For many purposes the temperature coefficient of resistance of alloys such as Eureka (Cu 60% + Ni 40%) and Manganincalloy of Copper + Magnganese + Nickle) and constantine is taken as negligible.
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