Question

why does resistance of a metallic conductor increase with increase in temperature​

Answer 1

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In a conductor, the charge carriers are electrons. As the temperature is increased, the collisions of these conduction electrons with the fixed ions of the lattice of the metal increases and hence the resistance of the conductor also increases.

Answer 2

In a conductor, the charge carriers are electrons. As the temperature is increased, the collisions of these conduction electrons with the fixed ions of the lattice of the metal increases and hence the resistance of the conductor also increases.