Question

Cause of helican motion of charged particle

Answer 1

Helical motion of charged particle in external magnetic field. When an electron moves in uniform external magnetic field, with velocity not perpendicular, I understand that the magnitude of force is only due to the perpendicular component of velocity and is perpendicular to both components of velocity.

Answer 2

the centripetal force produces a circular motion and the component of motion along the field converts that into a helix.
a magnetic field through which an electrically charged particle is moving will generally cause that particle to move with a helical motion .
hope it helps you