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When a charged particle moving with velocity $\vec v$ is subjected to a magnetic field of induction $\vec B$, the force on it is non-zero. This implies that
angle between is either zero or $180^o$
angle between is necessarily $90^o$
angle between can have any value other than $90^o$
angle between can have any value other than zero and $180^o .$
Solution
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 $180^{\circ} .$
