d
Force acting on a charged particle moving with velocity \(\vec{v}\) is subjected to magnetic field \(\vec{B}\) is given by

\(\vec{F}=q(\bar{v} \times \vec{B}) \quad \text { or, } \quad F=q v B \sin \theta\)

\((i)\) When \(\theta=0^{\circ}, F=q v B \sin 0^{\circ}=0\)

\((ii)\) When \(\theta=90^{\circ}, F=q v B \sin 90^{\circ}=q v B\)

\((iii)\) When \(\theta=180^{\circ}, F=q v B \sin 180^{\circ}=0\)

This implies force acting on a charged particle is non-zero, when angle between \(\bar{v}\) and \(\bar{B}\) can have any value other than zero and \(180^{\circ} .\)