A current l is passing through a wire having two sections P and Q… - Vidyadip

MCQ

A current $l$ is passing through a wire having two sections $P$ and $Q$ of uniform diameters $d$ and $d / 2$ respectively. If the mean drift velocity of electrons in sections $P$ and $Q$ is denoted by $v$ and $v_4$ respectively, then

A
$v=v$
B
$v=\frac{1}{2} v$
✓
$v=\frac{1}{4} v_4$
D
$v=2 v$

✓

Answer

Correct option: C.

$v=\frac{1}{4} v_4$

$\text { Drift velocity } v_d=\frac{i}{n e A} \Rightarrow v_d \propto \frac{1}{A} \text { or } v_d \propto \frac{1}{d^2} $
$ \Rightarrow \frac{v_P}{v_Q}=\left(\frac{d_Q}{d_P}\right)^2=\left(\frac{d / 2}{d}\right)^2=\frac{1}{4} \Rightarrow v_P=\frac{1}{4} v_Q.$

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