A pair of long conducting rails are held vertical at a separation `l = 50 cm`. The top ends are connected by a resistance of `R = 0.5 Omega` and a fuse (F) of negligible resistance. A conducting rod is free to slide along the rails under gravity. The whole system is in a uniform horizontal magnetic field B = 1.5 T as shown. Resistance of the rod and rails are negligible and the rod remains horizontal as it moves. The rod is released from rest. Find the minimum mass of the rod that will ensure that the fuse blows out. It is known that rating of the fuse is 4 A.

Answer

`0.3 kg`