A conducting wire of length L, uniform area of cross-section A of a material having n free electrons per unit volume offers a resistance R to flow of current through itself. (m and e respectively denote the mass and charge of electron). If τ is mean free time of free electrons in the conductor, the correct formula for resistance R is:
1
\(R = \frac{mL}{e^2 n A \tau}\)
2
\(R = \frac{mA}{e^2 n L \tau}\)
3
\(R = \frac{m \tau}{e^2 n AL}\)
4
\(R = \frac{e^2 n A \tau}{mL}\)