Question

A square coil $ACDE$ with its plane vertical is released from rest in a horizontal uniform magnetic field $\overset{ \rightarrow }{\text{B}}$ of length $2L$ . The acceleration of the coil is

• A. less than $g$ for all the 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 enters and comes out of the field but equal to $g$ when it is within the field.

Answer 1

Answer: (D)

When the coil is within the field, there is no change in magnetic flux passing through it. Thus, no current will be induced and the acceleration will be $g$ . But according to Lenz's law, the induced current will oppose its motion when it enters or leaves the field. Therefore, acceleration will be less than $g$ .