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Explain the variation of conductivity with temperature for (i) a metallic conductor, (ii) ionic conductors and (iii) semiconductors.

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Conductivity of a metallic conductor σ = \(\frac{1}{p}=\frac{ne^2r}{m}.\)

Where m = mass of charge carrier, e = charge on each carrier

τ = relaxation time, n = number density of charge carriers

(i) With rise of temperature, the collision of electrons with fixed lattice ions/atoms increases so that relaxation time (τ) decreases. Consequently, the conductivity of metals decreases with rise of temperature.

(ii) Conductivity of ionic conductor increases with increase of temperature because with increase of temperature, the ionic bonds break releasing positive and negative ions which are charge carriers in ionic conductors.

(iii) In the case of a semiconductors, when temperature increases, covalent bonds break and charge carriers (electrons and holes) become free i.e., n increases, so conductivity increases with rise of temperature.

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