Q. A uniform magnetic field acts at right angles to the direction of motion of electrons. As a result, the electron moves in a circular path of radius $2\ cm$. If the speed of the electrons is doubled, then the radius of the circular path will be
A) 2.0 $cm$
B) 0.5 $cm$
C) 4.0 $cm$
D) 1.0 $cm$
Explanation
(c) $r = \frac{mv}{qB} \Rightarrow r \propto v \Rightarrow r_{2} = 2r_{1} = 2 \times 2 = 4cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.