Question

Two identical circular loops of metal wire are lying on a table without touching each other. Loop - A carries a current that increases with time. In response, the loop - B is _____.

Answer 1

1. The curves with solid arrows show the direction of magnetic field lines. Loop- A with current flowing in it produces a magnetic flux through B as shown in the figure.
2. As the current increases, in response, Loop B will produce a current in the opposite direction to resist the increase in flux.
3. Let loop- A have an anticlockwise current through it. Thus the flux is coming out of the plane of the loop inside.
4. As the current in the loop- A increases with time, the flux it produces around is growing with time.
5. It acts as a bar magnet with a north pole outside the plane. Thus, the magnetic flux due to this loop is increasing in loop- B in the plane direction.
6. According to the Lenz Law, the current is induced in the loop - B such that the induced magnetic field opposes the change in the flux.
7. Thus the induced magnetic flux in the loop - B is also out of the plane. It also acts as a bar magnet with the north pole out of the plane of the loop- B
8. Hence, they repel each other.

Hence, two identical circular loops of metal wire are lying on a table without touching each other. Loop - A carries a current that increases with time. In response, the loop - B is repelled by Loop –A.