If a charged particle goes unaccelerated in a region containing electric and magnetic fields,

Options

A. `vecE` must be perpendicular to `vecB`
B. `vecv` must be perpendicular to `vecE`
C. `vecv` must be perpendicular to `vecB`
D. E must be equal to vB

Answer

(a,b)

Explanation

If a charged particle goes unaccelerated in a region containing
electric and magnetic fields,
`|qvecE|=|qvecvxxvecB| implies |vecE|=|vecvxxvecB| implies E = vB sin theta`