A moving charged particle, experiencing a magnetic field, always experience a force.

The force is

$$\mathbf{F}=q\mathbf{v}\times\mathbf{B}$$

where

- \(q\) is the charge of the particle,

- \(\mathbf{v}\) is its velocity and

- \(\mathbf{B}\) is the magnetic field, the force

If \(\mathbf{v}\) is parallel to \(\mathbf{B}\), then the cross product \(\mathbf{v}\times\mathbf{B}=0\), and there is no force acting on a particle.