If $n,\,e,\,\tau $ and $m$ respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length $l$ and area of cross-section $A$ will be
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(a) $R = \rho \frac{l}{A} = \frac{n}{{n{e^2}\tau }}.\frac{l}{A}$
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