The resistance of all pure metallic conductors’ increases with the increase in temperature but the resistance of the inculcators and other non-metallic materials generally decrease with the increase in temperature.

Experiments have shown that resistance of any pure metal conductor increases with the increase in temperature according to straight line law, as shown in. This property of conductor is untilled in manufacturing resistance thermo-meters.

The temperature coefficient of resistance is defined as the ratio of increase in resistance per degree rise of temperature to the original resistance and is represented by ∝ (alpha).

If R₀ is the resistance at 0⁰C and ∝₀ is the temperature coefficient of resistance at 0⁰C then resistance at t⁰C is given by

R_t = Original resistance + increase in resistance = R₀ + R₀∝₀t = R₀(1+ ∝₀t)

It is to be noted that

(i)    temperature coefficient of resistance depends upon the temperature.

(ii)    temperature coefficient of resistance for all pure metallic conductors is positive, i.e. the resistance of all pure metallic conductors increases with the increase in temperature, that of non-metallic materials such as of carbon is negative i.e., the resistance of non-metallic materials such as of carbon decreases with the increase in temperature like constantan and manganin.

(iii)    As resistance the material changes with the changes with the change in temperature so it is obvious that resistively of materials depends on the temperature.

Knowledge of temperature coefficient of resistance is untilled in determining the temperature of electrical machines.

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