A current $I$ 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 $v_P$ and $v_Q$ respectively, then
  • A$v_P = v_Q$
  • B$v_P = \frac{1}{2}v_Q$
  • C$v_P = \frac{1}{4}v_Q$
  • D$v_P = 2 v_Q$
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