Q.

A proton moving with a constant velocity passes through a region of space without any change in its velocity. If E¯ and B¯ represent the electric and magnetic fields respectively, then the region of space may have:

(A) E = 0, B = 0                                (B) E = 0, B ≠ 0

(C) E ≠ 0, B = 0                                (D) E ≠ 0, B ≠ 0

Choose the most appropriate answer from the options given below:                                   [2024]

1 (A), (B) and (C) only  
2 (A), (C) and (D) only  
3 (A), (B) and (D) only  
4 (B), (C) and (D) only  

Ans.

(3)      

          Net force on particle must be zero i.e.

           qE+qV×B=0

           Possible cases are

           (i)  E and B=0

           (ii)  V×B=0,E=0

           (iii)  qE=-qV×B

            E0 and B0