In the free-electron model, the drift velocity acquired by electrons i…

Question

In the free-electron model, the drift velocity acquired by electrons in a steady field E (with $	au$ the relaxation time, e and m the electron charge and mass) has magnitude

Accepted Answer

A. $v_d = \dfrac{eE	au}{m}$

1. An electron accelerates as $a = eE/m$ between collisions.
2. Over the average time $	au$ between collisions, $v_d = a	au$.
3. Substituting, $v_d = eE	au/m$.
4. The other forms misplace $m$, $	au$, or $E$ and give wrong dimensions.
_Source: NCERT Class 12 Physics Ch 3 "Current Electricity", p.5_

Answer

$v_d = \dfrac{mE}{e	au}$

Answer

$v_d = \dfrac{eEm}{	au}$

Answer

$v_d = \dfrac{e	au}{mE}$

In the free-electron model, the drift velocity acquired by electrons in a steady field E (with $\tau$ the relaxation time, e and m the electron charge and mass) has magnitude