Q. A beam of cathode rays is subjected to crossed Electric (E) and Magnetic field (B). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by
A) $\frac{E^{2}}{2VB^{2}}$
B) $\frac{B^{2}}{2VE^{2}}$
C) $\frac{2VB^{2}}{E^{2}}$
D) $\frac{2VE^{2}}{B^{2}}$
Explanation
(a) $qvB = qE \Rightarrow v = \frac{E}{B}$
But$\ \frac{1}{2}mv^{2} = qV$ so$\ \frac{q}{m} = \frac{v^{2}}{2V} = \frac{E^{2}}{2VB^{2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.