Question

One conducting U tube can slide inside another as shown in figure, maintaining electric contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. If each tube moves towards the other at a constant speed v, then the emf induced in the circuit in terms of B, $l$ and v where $l$ is the width of each tube, will be

• A. -B$l$v
• B. B$l$v
• C. 2 B$l$v
• D. zero

Answer 1

Answer: (C)

2 B$l$v

Relative velocity $=v+v=2v$
Therefore, $emf=Bl\left(2v\right)$