Q. An electron initially at rest, is accelerated through a potential difference of $200\ volt,$ so that it acquires a velocity $8.4 \times 10^{6}m/s.$ The value of $e/m$ of electron will be
A) $2.76 \times 10^{12}C/kg$
B) $1.76 \times 10^{11}C/kg$
C) $0.76 \times 10^{12}C/kg$
D) None of these
Explanation
(b) $\frac{1}{2}mv^{2} = eV \Rightarrow \frac{e}{m} = \frac{v^{2}}{2V} = \frac{\left( 8.4 \times 10^{6} \right)^{2}}{2 \times 200} = 1.76 \times 10^{11}\frac{C}{kg}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.