A current $I$ flows through a uniform wire of diameter $d,$ when the mean drift velocity is $v_d.$ The same current will flow through a wire of diameter $d/2$ made of the same material, if the mean drift velocity of the electrons is
  • A$\frac {v}{4}$
  • B$\frac {v}{2}$
  • C$4v$
  • D$2v$
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