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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

Asked in JEE Main 2005 · Free conductor moving in a field

Figure: Free conductor moving in a field
Answer: (2) 2Blv

Step-by-step solution

Each tube moves at v, so the width of the circuit closes at the relative rate 2v.

ε=Bℓ(2v)=2Bℓ v.

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