Q. Electrons ejected from the surface of a metal, when light of certain frequency is incident on it, are stopped fully by a retarding potential of 3 V. Photoelectric effect in this metallic surface begins at a frequency $6 \times 10^{14}\ s^{- 1}$. The frequency of the incident light in $s^{- 1}$ is [Planck’s constant = $6.4 \times 10^{- 34}\ Js,$ charge on the electron = $1.6 \times 10^{- 19}$C]
A) $7.5 \times 10^{13}$
B) $13.5 \times 10^{13}$
C) $13.5 \times 10^{14}$
D) $7.5 \times 10^{15}$
Explanation
(c) Einstein’s photoelectric equation is given by
$hv = hv_{0} + \phi = hv_{0} + eV$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ v = v_{0} + \frac{eV_{0}}{h}$
$= \ (6 \times 10^{14}) + \frac{\left( 1.6 \times 10^{- 19} \right)(3)}{(6.4 \times 10^{- 34})}$
= 13.5$\times 10^{14}\ s^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.