$A$ long conducting wire having a current $I$ flowing through it is bent into a circular coil of $N$ turns. Then it is bent into a circular coil of $n$ turns. The magnetic field is calculated at the centre of the coils in both cases. The ratio of the magnetic field in the first case to that of the second case is:

  • A
    $N : n$
  • B
    $n^2 : N^2$
  • C
    $N^2 : n^2$
  • D
    $n : N$

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