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

If both E and B are zero, then `F_(e)` and `F_(m)` both are zero. Hence, velocity may remain constant. Therefore, option (A) is correct.
If `E=0,B!=0` but velocity is parallel or antiparallel to magnetic field, then also `F_(e)` and `F_(m)` both are zero.
Hence, option (B) is also correct.
If but then also velocity may remain constant or option (D) is also correct. If `E!=0,B!=0` but `F_(e)+F_(m)=0` then also velocity may remain constant or option (D) is also correct.