JEE Main201815 Apr 2018Evening ShiftPhysicsElectromagnetic InductionActual
A copper rod of mass m slides under gravity on two smooth parallel rails, with separation l and set at an angle of with the horizontal. At the bottom, rails are joined by a resistance R. There is a uniform magnetic field B normal to the plane of the rails, as shown in the figure. The terminal speed of the copper rod is:
Options
- AmgR B ^2 l^2
- BmgR B ^2 l^2
- CmgR B ^2 l^2
- DmgR B ^2 l^2
Correct answer
B. mgR B ^2 l^2
Step-by-step solution
From Faraday's law of electomagnetic induction, aligned e &= d d t = d(B A) l t = d(B l l) d t &= B d l l d t =B V l aligned Also, F=i l B= ( B V R ) (l^2 B )= B^2 l^2 V R At equilibrium m g = B^2 l V R V= m g R B^2 l^2