$A$ straight rod of mass $m$ and length $L$ is suspended from two identical springs as shown in the figure. The springs are stretched by a distance of $x_0$ due to the weight of the rod. The circuit has a total resistance $R$. When a magnetic field perpendicular to the plane of the paper is switched on,the springs are observed to extend further by the same distance $x_0$. The magnetic field strength is:

  • A
    $\frac{mgR}{\varepsilon L}$; directed outward from the plane of the paper
  • B
    $\frac{mgR}{2\varepsilon x_0}$; directed outward from the plane of the paper
  • C
    $\frac{mgR}{\varepsilon L}$; directed into the plane of the paper
  • D
    $\frac{mgR}{2\varepsilon x_0}$; directed into the plane of the paper

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