Question

The work function of a metal surface is 2.4eV. Calculate
(i) Maximum wavelength of photon which can eject electrons from the metal.
(ii) The maximum kinetic energy of photoelectrons emitted by a photon of 3eV energy.
(iii) The retarding potential to stop the emission.

Answer 1

Work function of metal surfaces is $2.4eV$ to calculate :-

i) Maximum wavelength of photon which can eject electron from the metals. firstly we will find the kinetic energy.

Kinetic energy $=$ energy of the incident light energy $-$ work function

ii) $\therefore K.E_{\left(max\right)}=3ev-2.4ev$

$=0.6ev$

(i) $E=\frac{hc}{\lambda }$

$3=\frac{1.99\times {10}^{-25}}{\lambda }[\therefore h$ is the plank's constant and $c$ is the speed of light ]

$\lambda =\frac{1.99\times {10}^{-25}}{3}$

$\lambda =0.663\times {10}^{-25}m$.

(iii) now, retarding potential $\left(V_0\right)$ will be given by :

$V_0=\frac{k_{max}}{e}=\frac{0.6}{3}=0.2$

$V_0=0.2m/s$