Two planar concentric rings of metal wire having radii $r_1$ and $r_2$ (with $r_1 > r_2$) are placed in air. The current $I$ is flowing through the coil of larger radius. The mutual inductance between the coils is given by ($\mu_0$ = permeability of free space)

  • A
    $\frac{\mu_0 \pi r_1^2}{2 r_2}$
  • B
    $\frac{\mu_0 \pi r_2^2}{2 r_1}$
  • C
    $\frac{\mu_0 \pi (r_1 + r_2)^2}{2 r_1}$
  • D
    $\frac{\mu_0 \pi (r_1 - r_2)^2}{2 r_2}$

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