Q. If $e/m$ of electron is $1.76 \times 10^{11}$ C ${kg}^{- 1}$ and stopping potential is 0.71 V, then the maximum velocity of the photoelectron is

A) 150 km/s
B) 200 km/s
C) 500 km/s
D) 250 km/s
Explanation

(c) $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \frac{1}{2}mv^{2} = eV$
$v\ = \sqrt{\frac{2eV}{m}} = \sqrt{2V \times \frac{e}{m}}$
$v = \ \sqrt{2 \times 0.91 \times 1.76 \times 10^{11}}$
$\ \ = 5 \times 10^{5}m/s$
= 500Km/s

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.