In a conductor, if the number of conduction electrons per unit volume
Question:

In a conductor, if the number of conduction electrons per unit volume is $8.5 \times 10^{28} \mathrm{~m}^{-3}$ and mean free time is $25 \mathrm{fs}$ (femto second), it’s approximate resistivity is: $\left(\mathrm{m}_{\mathrm{e}}=9.1 \times\right.$ $10^{-31} \mathrm{~kg}$ )

1. (1) $10^{-6} \Omega m$

2. (2) $10^{-7} \Omega \mathrm{m}$

3. (3) $10^{-8} \Omega \mathrm{m}$

4. (4) $10^{-5} \Omega \mathrm{m}$

Correct Option: , 3

Solution:

(3) $\rho=\frac{m}{n e^{2} \tau}$

$=\frac{9.1 \times 10^{-31}}{8.5 \times 10^{28} \times\left(1.6 \times 10^{-19}\right)^{2} \times 25 \times 10^{-15}}$

$=10^{-8} \Omega-\mathrm{m}$

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