$A$ and $B$ are two concentric circular conductors of centre $O$ and carrying currents ${i_1}$ and ${i_2}$ as shown in the adjacent figure. If ratio of their radii is $1 : 2$ and ratio of the flux densities at $O$ due to $A$ and $B$ is $1 : 3$, then the value of ${i_1}/{i_2}$ is

128-69

  • A

    $\frac{1}{6}$

  • B

    $\frac{1}{4}$

  • C

    $\frac{1}{3}$

  • D

    $\frac{1}{2}$

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