Question

A particle moves in a region with 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
(a) a straight line
(b) a circle
(c) a helix with uniform pitch
(d) a helix with non-uniform pitch

Answer 1

(d)The path of the particle will be a helix with non-uniform pitch.

Explanation:

Here, on the particle, the total Lorentz force exerted is expressed as below:

F = qE + qVB  

• It is known that the speed of the particle’s direction does not change with the magnetic field B.
• As the electric field present accelerates the particle in the field direction, the resultant path is a non-uniform pitch and the resultant path is a helix.