| 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 is the width of each tube, will be: |
 |
A) \[Blv\]
B) \[-\,Blv\]
C) zero
D) \[2Blv\]
Correct Answer: D
Solution :
Induced emf due to motional emf is produced in both tube \[\vec{e}=(\vec{v}\,\,\times \,\,\vec{B}).\,\vec{L}\] Here \[\vec{v},\] \[\vec{B}\] and \[\vec{L}\] are mutually perpendicular to each other. \[\therefore e=BvL\] Equivalent circuit is shown
Equivalent emf \[e=Blv+Blv=2Blv\]
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