Q. An electron is moving with a speed of $10^{8}\ ms^{- 1}$ perpendicular to a uniform magnetic field of induction B. Suddenly induction of magnetic field is reduced to B/2. The radius of the path becomes from the original value of r
A) No change
B) Reduces to r/2
C) Increases to 2r
D) Stops moving
Explanation
(c) $B\ e\ v = mv^{2}/r$ or $B \propto 1/r$ ; so, $r_{2} = r_{1}\ B_{1}/B_{2}$
$= r\ B\ /(B$/2)= 2$r$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.