Q138 / 180 · COMEDK 2018 · Physics
A metal wire is subjected to a constant potential difference. When the temperature of the metal wire increases, the drift velocity of the electron in it
- Aincreases, thermal velocity of the electron decreases
- Bdecreases, thermal velocity of the electron decreases
- Cincreases, thermal velocity of the electron increases
- Correct answerDdecreases, thermal velocity of the electron increases
Solution
Drift velocity of the electron is given as
$$
v_{d}=\frac{e E \tau}{m}
$$
where, $e=$ charge on electron,
$E=$ electric field,
$\tau=$ relaxation time
and $m=$ mass of the electron.
Since,
$$
\therefore \quad v_{d}=\frac{e V \tau}{m l}
$$
Since, $e, V, m$ and $l$ are constant .
$$
\therefore \quad v_{d} \propto \tau
$$
On increasing the temperature of metal wire, relaxation time decreases, therefore drift velocity of electrons also decreases.
But on increasing temperature of metal wire, thermal velocity of electron increases.
Hence, the correct answer is option: 'D'.