Two concentric circular coils $A$ and $B$ have radii $20 \text{ cm}$ and $10 \text{ cm}$ respectively and lie in the same plane. The current in coil $A$ is $0.5 \text{ A}$ in the anticlockwise direction. What is the current in coil $B$ such that the net magnetic field at the common centre is zero?

  • A
    $0.5 \text{ A}$ in the anticlockwise direction
  • B
    $0.25 \text{ A}$ in the anticlockwise direction
  • C
    $0.25 \text{ A}$ in the clockwise direction
  • D
    $0.125 \text{ A}$ in the clockwise direction

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