Two concentric circular coils $A$ and $B$ having radii $20 \ cm$ and $10 \ cm$ respectively lie in the same plane. The current in coil $A$ is $0.5 \ A$ in anticlockwise direction. The current in coil $B$,so that net magnetic field at the common centre is zero,is

  • A
    $0.5 \ A$ in anticlockwise direction.
  • B
    $0.25 \ A$ in anticlockwise direction.
  • C
    $0.25 \ A$ in clockwise direction.
  • D
    $0.125 \ A$ in clockwise direction.

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