A loop, carring a current i, lying in the plane of the paper, is in the field of a long straight wire with current `i_0` (inward) as shown in Fig. Find the torque acting on the loop.

Answer

`(epsilon_(0)lB)/(sigma)`

Explanation

The net electric field `E=vec(E)_(1)+vec(E)_(2)`
`impliesE=(sigma)/(2 epsilon_(0))+(sigma)/(2 epsilon_(0))+(sigma)/(epsilon_(0))`
The net force acting on the electron is zero because it move with constant
velocity `implies vec(F)_(n e t)=vec(F)_(c)_vec(F)_(m)=0`
`implies|vec(F)_(c)|=|vec(F)_(m)|implieseE=evBimpliesv=(E)/(B)=(sigma)/(epsilon_(0)B)`
`:.` The time of motion in side of the capacitor `=t=(l)/(v)=(epsilon_(0)lB)/(sigma)`