Question

A square coil $ACDE$ with it's plane vertical is released from rest in a horizontal uniform magnetic field $\overrightarrow{B}$ of length $2L$ ( as shown in figure). The acceleration of the coil is

• A. less than $g$ for all time till the loop crosses the magnetic field completely
• B. less than $g$ when it enters the field and greater than $g$ when it comes out of the field
• C. $g$ all the time
• D. less than $g$ when it enters and comes out of the field but equal to $g$ when it is within the field

Answer 1

The correct option is D less than $g$ when it enters and comes out of the field but equal to $g$ when it is within the field

Flux through the loop only changes when it enters and when it leaves the field. When it is fully inside the field or fully outside the field, the flux doesnt change.
When the flux changes, there is a current induced that opposes the cause according to Lenz's law. Therefore only when enetering and when leaving the field, the acceleration of the loop will be less than $g$. Other times, when it is fully inside the field or fully outside the field, the acceleration will be $g$.