[QUE/SM-09001] SM-SOLUTION

ANSWER :

In collision of electrons only a fraction close to the Fermi surface will undergo a change in energy. That fraction is \(\sim n\Big({\frac{kT}{\epsilon_F}}\Big)\)  of the electrons. Thus
\[ \text{Mean free path } \lambda = \frac{\epsilon_F}{n(k)\sigma^2} >> \frac{1}{n\sigma^2}.\]
Further \(\lambda \propto \frac{1}{T}\), as \(T\) increases \(\lambda\) will decrease.