Question

A particle moves in a region having a uniform magnetic field and a parallel, uniform electric field. At some instant, the velocity of the charged 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 a uniform pitch
• D. a helix with a non-uniform pitch.

Answer 1

The correct option is D a helix with a non-uniform pitch.

At the instant of starting, the path is a circle.The electric field causes the particle to accelerate perpendicular to the plane of the circle. Therefore, the path is a helix. In addition, because of the parallel electric field, v increases with time. Hence, the path will be a helix with a non-uniform pitch.