A straight rod of mass m and lenth `L` is suspended from the identical spring as shwon in the figure The spring strectched by a distance of `x_(0)` due to the weight of the wire The circuit has total resistance `Romega` When the magnetic field perpendicular to the plane of the paper is switched on, springs are observed to extend further by the same distance The magnetic field strenght is

Options

A. `2(mgR)/(LV)`
B. `(mgR)/(LV)`
C. `(mgR)/(2LV)`
D. `(mgR)/(V)`

Answer

A

Explanation

`mg = kx …(1)
`mg + ILB = k. 2x…(2)`
From(I) and (2)…(2)`
`ILB = mg implies B =(mg)/(IL) o.`
`B = (mgR)/(EL)o.` .