A rectangular wire-loop of width a is suspended from the insulated pan of a spring balance as shown in figure (34 - E5). A current i exists in the anticlock wise direction in the loop. A magnetic field B exists in the lower region. Find the change in the tension of the spring if the current in the loop is reversed.
Force in the lower side of rectingular loop due to current i in magnetic field B Initially when current is flowing in anticlockwise direction
Then F = iaB in right of a.
When current is reversed the rension is
F = iaB in left a
So, change in tension
= iaB - (- iaB) = 2 iaB.