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CBSE Class 12-science Answered

Write the mathematical relation for the resistivity of material in terms of relaxation time, number density and mass and charge of charge carriers in it. Explain, using this relation, why the resistivity of a metal increases and that of semi-conductor decreases with rise in temperature.
Asked by Topperlearning User | 27 Apr, 2015, 03:24: PM
answered-by-expert Expert Answer

Resistivity,

(i) Metals: As the temperature increases, the thermal speed of electrons increases. Free electrons collide more frequently with the positive metal ions. The relaxation time decreases. Consequently, the resistivity of the metal increases.

(ii) Semiconductors: The relaxation time does not change with the temperature. But the number density (n) of free electrons increases exponentially with temperature. As result, the sensitivity of semiconductor decreases exponentially with the increase in temperature.

Answered by | 27 Apr, 2015, 05:24: PM

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