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:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → $R=\frac{mL}{e^2nAτ}$
The formula for the resistance R is,
$R=ρ\frac{L}{A}$
and
Resistivity, $ρ\frac{m}{ne^2τ}$
$⇒R=\frac{mL}{ne^2τA}$