Let `vecE and vecB` denote the electric and magnetic field in a certain region of space. A proton moving with a velocity along a straight line enters the region and is found to pass through it undeflected. Indicate which of the following statement are consistent with the observation.

Options

A. `barE=0` and `barB=0`
B. `barE ne 0` and `barB=0`
C. `vecE ne 0` and `vecB ne 0` and both `vecE` and `vecB` are parallel to `vecv`
D. `vecE` is parallel to `vecv` but `vecB` is perpendicular to `vecv`

Answer

A, B, C

Explanation

`vecV` constant in direction and may be in magnetude
`veca=0`
`qvecE+q(vecVxxvecB)=0`
`I^(st)` posibility
`vecE=0&vecB=0 to V`
`II^(nd)` posibility
`vecE=0&vecV||vecBi.e.vecBne0`
`III^(rd)` posibility
`toE=0& vecE||vecV&B=0`
`IV^(th)` posibility
`toB`
`toV vecE||vecV||vecB`
`toE vecVxxvecB=0`
`V^(th)` posibility
`qvecE=-q(vecVxxvecB)`