Q.

XPQY is a vertical smooth long loop having a total resistance R where PX is parallel to QY and the separation between them is l. A constant magnetic field B perpendicular to the plane of the loop exists in the entire space. A rod CD of length L (L>l) and mass m is made to slide down from rest under gravity as shown in the figure. The terminal speed acquired by the rod is _______ m/s. (g = acceleration due to gravity)                 [2026]

1 2mgRB2L2  
2 mgRB2l2  
3 8mgRB2l2  
4 2mgRB2l2  

Ans.

(2)

At equilibrium (or for terminal velocity)

mg=IB  mg=(BvR)B

V=mgRB22