Question

The ejection of the photo electron from the silver metal in the photo electric effect experiment can be stopped by applying the voltage of 0.35 vol. When the radiation 256.7 nm is used. The work function for silver metal is?

• A. 4.48 ev
• B. 3.35 ev
• C. 44.8 ev
• D. 22.4 ev

Answer 1

The correct option is A 4.48 ev

Solution:- (A) $4.48eV$

Given:-

From the principle of conservation of energy, the energy of an incident photon $\left(E\right)$ is equal to the sum of the work function $\left(W_0\right)$ of radiation and its kinetic energy $(K.E.)$ i.e.,

$E=W_0+K.E.$

$\Rightarrow W_0=E-K.E.$

As we know that,

$E=\frac{hc}{\lambda }$

Here,

$h=$ Planck's constant $=6.62\times {10}^{-34}J-s$

$c=$ Speed of light $=3\times {10}^{8}m/s$

$\lambda =$ Wavelength $=256.7nm=2.56\times {10}^{-7}m$

$\therefore E=\frac{6.62\times {10}^{-34}\times 3\times {10}^8}{2.56\times {10}^{-7}}=7.74\times {10}^{19}J=4.83eV$

Since the potential applied gives the kinetic energy to the radiation, therefore,

K.E of the electron $=0.35eV$

Therefore,

$W_0=4.83-0.35=4.48eV$

Hence the work function is $4.48eV$.