Two parallel long wires carry currents $i_1$ and $i_2$ with ${i_1} > {i_2}$. When the currents are in the same direction, the magnetic field midway between the wires is $10\, \mu T$. When the direction of $i_2$ is reversed, it becomes $40 \,\mu T$. the ratio ${i_1}/{i_2}$ is

  • A

    $3 : 4$

  • B

    $11 : 7$

  • C

    $7 : 11$

  • D

    $5 : 3$

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  • [KVPY 2016]