Question

A charged particle moves in a uniform magnetic field. The velocity of the particle at some instant makes an acute angle with the magnetic field. 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:  

• It is understood from the figure that the particle’s velocity can be determined in two components, Vsin θ perpendicular to the magnetic field and Vcos θ parallel to the magnetic field.

• The speed of the particle cannot be changed by the magnetic field, rather the velocity’s direction can be changed.

• A magnetic force shows an effect on the particle due to the velocity’s vertical component, which attempts to transfer the unit in a circle.

• The particle is rotated in a circle by this force.