A particle moves in a region having a uniform magnetic field and a parallel, uniform electric field. At some instant, the velocity of the particle is perpendicular to the field direction. The path of the particle will be

Options

A. a straight line
B. a circle
C. a helix with uniform pitch
D. a helix with increasing pitch.

Answer

D

Explanation

`F_(E)=q_(E),F_(m)=qvB`
`R=(mv)/(qB)`
pitch `p=V_(||)=0+(qEt)/m`