A positive charge moves with speed v parallel to a uniform magnetic field B. The magnetic force on the charge is:

1. Magnetic force magnitude: $F = qvB\sin\theta$. 2. When $\mathbf{v}$ is parallel to $\mathbf{B}$, the angle $\theta = 0^\circ$. 3. Then $\sin 0^\circ = 0$, so $F = 0$. 4. The vector product vanishes when velocity and field are parallel. _Source: NCERT Class 12 Physics Ch 4 "Moving Charges and Magnetism", p.135_