Question

A square coil ACDE with its plane vertical I released from rest in a horizontal uniform magnetic field $\overrightarrow{B}$ of length 2L. The acceleration of the coil is.
a) g all the time
b) less than g when it enters the field and greater than g when it comes out of the field
c) less than g when it enters and comes out of the field but equal to g when it is within the field
d) Less than g for all the time till the loop crosses the magnetic field completely

Answer 1

Hint: This question is a problem of electromagnetic induction phenomenon. For solving this question, we will be using the Lenz Law. This law states “the direction of the electric current which is induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.”

Complete step by step answer:
Now, according to the Lenz Law,
The flux passing through a loop changes only when it enters and leaves the magnetic field. When it is completely inside the magnetic field or completely outside the magnetic field, the flux does not change.
When there is a current induced which opposes the cause, the flux changes in accordance with Lenz's law. Therefore, the acceleration of the loop will be less than g only while entering the field and while leaving the field. And, the acceleration will be g when it is completely inside the field or completely outside the field.

So, the correct answer is “Option C”.

Note: Lenz Law was named after the Russian physicist Heinrich Friedrich Emil Lenz, who found this law in 1834. He was born on 12 February 1804 in Tartu, Estonia. He was of German Descent and died on 10 February 1865 in Rome, Italy.