A proton moving with a constant velocity passes through a region of space without any changing its velocity. If `E` and `B` represent the electric and magnetic fields, respectively. Then, this region of space may have

Options

A. `E=0, B=0`
B. `E=0, B!=0`
C. `E!=0, B=0`
D. `E!=0, B!=0`

Answer

A, B, D

Explanation

When `E!=0`, the velocity of proton changes as `F_e=qE` when `B!=0`, velocity of proton may be parallel or antiparallel to that of field as such `F_m=0` and velocity of proton does not change. Thus, : (a) When `E=0`, `B=0`, `F_e=F_m=0`, velocity doesn't change
(b) When `E=0`, `B!=0`, proton moves along `vecB` and velocity doesn't change.
(d) When `E!=0`, `B!=0`, `F_e` and `F_m` may balance each other.