Question

A vertical conducting ring of radius R falls vertically under gravity in a horizontal magnetic field of magnitude $B_0$. Direction of $B_0$ is perpendicular to the plane of ring. when speed of ring becomes $v$,

• A. Points C and D are at same potential.
• B. Points A and B are at same potential.
• C. Time to gain speed $v$ is more than $\frac{v}{g}$
• D. No current flow in ring.

Answer 1

Answer: (A), (C)

Time to gain speed $v$ is more than $\frac{v}{g}$


EMF across AB is BVl. So, there will be a charge movement and accumulation from B to A, until the electrostatic potential difference becomes equal to the EMF across A to B. Since, $v$ is increasing, the EMF is also increasing, so there will be a continuous flow of charges from B to A. Because of this current, there will be a force on the ring in the upward direction. So the acceleration of the ring is less than $g$, so the time taken is more than $\frac{v}{g}$.
The line joining C and D is along the direction of speed, so there is no induced EMF across C and D.