JEE Advanced Model Paper 7 with solutions for online practice

A thin, uniform rod with negligible mass and length ‘l ’ is attached to the floor by africtionless hinge at a point P. A horizontal spring with force constant ‘ k ’ connects the otherend of the rod to a vertical wall. The rod is in a uniform magnetic field ‘B’ directed into theplane of the figure. There is current ‘i ’ in the rod, in the direction shown. When the rod is inequilibrium and makes an angle of 30° with the floor, the spring is stretched by x =

nBil

k

. The value of n is________