Motion of a charged particle having velocity v in a uniform magnetic field B is circular, if v is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → perpendicular to B
The magnetic force is $F = q(\vec{v} \times \vec{B})$
If $\vec{v} \perp \vec{B}$, force is maximum and acts as centripetal force → circular motion.
If $\vec{v} \parallel \vec{B}$ or $\vec{v} \; \text{anti-parallel to} \; \vec{B}$, then $F=0$ → straight motion.
If $\vec{v}$ at any other angle to $\vec{B}$, motion is helical.
Hence, motion is circular if:
${\text{perpendicular to B}}$