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logearav

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## Homework Statement

Revered Members,

When we increase the temperature, resistance increases in conductors. But resistance decreases in semiconductors. Why?

Help in this regard will be highly appreciated.

## Homework Equations

## The Attempt at a Solution

Due to increase in temperature, covalent bonds gets broken and free electrons are generated in semiconductors.

In the case of conductors, when we increase the temperature free electrons collide with the lattice and for every collision they lose energy and resistance increases.

In semiconductors too, free electrons collide with the lattice, but their resistance, in contrary, decreases? Why?

Also, R = ml/ne

^{2}A[itex]\tau[/itex]

where m is the mass of electron, l is the length of the conductor, n is the number of free electrons per unit volume and e is 1.602*10

^{-19}Coulomb, A is cross sectional area of conductor and [itex]\tau[/itex] is relaxation time.

In conductors, [itex]\tau[/itex], decreases when the temperature increases, so Resistance increases, I presume. But why [itex]\tau[/itex] decreases, when temperature increases.