Three materials A, B and C have electrical conductivities `sigma , 2 sigma` and `2 sigma` respectively. Their numbers densities of free electrons are 2 n, n and 2n respectively. For which material is a average collision time of free electrons maximum?

Three materials A, B and C have electrical conductivities `sigma , 2 s

1.	Three materials A, B and C have electrical conductivities `sigma , 2 sigma` and `2 sigma` respectively. Their numbers densities of free electrons are 2 n, n and 2n respectively. For which material is a average collision time of free electrons maximum?
Answer» Conductivity `sigma=1/rho = (n e^(2) tau)/m` Relaxation time, `tau = (m sigma)/(n e^(2)`. i.e., `tau prop sigma/n` `:. tau_(A) : tau_(B):tau_(C) = sigma/2n : 2sigma/n : 2sigma/2n = sigma/2n : 2sigma/n : sigma/n` Thus, `tau_(B) gt tau_(C ) gt tau_(A)`. So average collision time for material B is maximum.

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Three materials A, B and C have electrical conductivities `sigma , 2 sigma` and `2 sigma` respectively. Their numbers densities of free electrons are 2 n, n and 2n respectively. For which material is a average collision time of free electrons maximum?

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