The ratio of the magnetic field at the centre of a circular ring of radius $R$ to the magnetic field at a point on its axis at a distance $2\sqrt{2}R$ from its centre is . . . . . .

  • A
    $27:1$
  • B
    $81:1$
  • C
    $1:9$
  • D
    $1:2\sqrt{2}$

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