Q.

A metallic rod of mass per unit length 0.5 kg m-1 is lying horizontally on a smooth inclined plane which makes an angle of 30° with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is   [2018]
 

1 7.14 A  
2 5.98 A  
3 14.76 A  
4 11.32 A  

Ans.

(4)

Mass per unit length of a metallic rod is ml=0.5 kg m-1.

Let I be the current flowing.

For equilibrium, mgsin30°=IlBcos30°

I=mglBtan30°=0.5×9.80.25×3=11.32A