Q.

A proton, a deuteron and an α particle with the same KE enter in a region of uniform magnetic field, moving at right angles to magnetic field. What is the ratio of the radii of their circular paths

1 1:2:1  
2 1:2:2  
3 2:1:1  
4 2:2:1  

Ans.

(1)

rp=2mpKeB    rd=2(2mp)KeB    ra=2(4mp)K(2e)B