Question

One conducting U tube can slide inside another as shown in figure maintaining electrical 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. $Blv$
• B. $-Blv$
• C. Zero
• D. $2Blv$

Answer 1

The correct option is D

$2Blv$

Let $v_{\text{rel}}$ be the relative velocity of one tube with respect to the other.

Then

$\xi =\text{B}\times \text{width of the tube}\times v_{\text{rel}}$

$=\text{B}\times l\times [v-(-v\left)\right]$

$=2\text{B}lv$