Q. A electron moving with a variable linear velocity $v$ in a variable magnetic field $B$ will remain rotating in a circle of constant radius $r$ only when
A) $B$ is held constant
B) $v$ is held constant
C) Both $v$ and $B$ are constant
D) None of the above
Explanation
(c) For a charged particle in magnetic field $B,\ r = m\ v/qB$. The radius can be fixed for a charged particle if $v$ and $B$ both are fixed
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.