Question

Two identical coaxial circular loops carry a current( I) each circulating in the same direction. If the loops approach each other, you will observe that the current in
A. Each increase
B. Each decrease
C. Each remains the same
D. One increased whereas that in the other decreases

Answer 1

Hint: When a charge moves in an electric field, work is done on it by the electric field lines. Due to this force charge gains some momentum and velocity. Therefore, this gained velocity/speed produces a magnetic field. Further, what happens when magnetic flux changes, is explained by Lenz law, which we will discuss here.

Complete step by step solution:
According to the Lenz law, when magnetic flux changes in a conductor an induced emf is generated which in turn creates induced current which opposes the change in the initial magnetic flux of the conductor.
Let us now apply the Lenz law in our question. We have two identical coaxial circular loops carrying I current each in the same direction. Now when we bring the circular loop closer to the other, the magnetic flux through each loop increases due to the other loop. So, to oppose this change in flux induced current will be generated in the opposite direction. Therefore, the net current in the loops decreases.
Hence, the correct option is (B) each decrease.

Note:
It is important to keep in mind that the induced current will be in the opposite direction of the initial current.
Lenz law makes it easy to find the direction of many electromagnetic effects.
The strength of this magnetic field depends on the velocity gained by the charge.