In a conductor, if the number of conduction electrons per unit volume is $8.5 \times 10^{28}\, m^{-3}$ and mean free time is $25\,fs$ $($femto second$),$ its approximate resistivity is $\left( {{m_e} = 9.1 \times {{10}^{ - 31}}\,kg} \right)$
JEE MAIN 2019, Medium
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$\rho = \frac{{2m}}{{n{e^2}\tau }}$
$= 3.34 \times {10^{ - 8}}\,\Omega \,m$
$= 3.34 \times {10^{ - 8}}\,\Omega \,m$
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