Q 12-03-187JEE MainJEE Main 2021 (27 Jul, Shift 1)Easy
In the given figure, a battery of emf $E$ is connected across a conductor $PQ$ of length $l$ and different area of cross-sections having radii $r_1$ and $r_2$ $(r_2 < r_1)$.
Choose the correct option as one moves from $P$ to $Q$.
Answer: (A) Drift velocity of electron increases.
The current $I$ is the same through every cross-section (series), so the electron current does not change.
$v_d = \dfrac{I}{neA}$: as $A$ decreases from $P$ to $Q$, $v_d$ increases.
$E = \rho J = \dfrac{\rho I}{A}$ also increases. So only option (1) is correct.
Solution by Sreeraj P, M.Sc Physics