Question

Light of wavelength $488 \,nm$ produced by an Agron laser is used in the photoelectric effect. When light from this spectral line is incident on the cathode, the stopping potential of the photoelectrons is $0.38 \,V$. The Work function of the cathode material is

• A. 2.16 eV
• B. 216 eV
• C. 21.6 eV
• D. 0.216 eV

Answer 1

Answer: (A)

Given, light of wavelength, $\lambda=488 \,nm$ and stopping potential, of photoelectrons, $V=0.38 \,V$
As, energy of photon
$E =\frac{h c}{\lambda}=\frac{1250}{488} \,eV$
So, $ E =2 \cdot 56\, eV$
$\because$ Maximum kinetic energy of a photo-electron
$KE _{\max }=e V_{0}$
Where, $V_{0}=$ stopping potential
$\therefore \, KE _{\max }=e V_{0}=0.38\, eV$
From Einstein's photoelectric equation,
$ E= KE _{\max }+W_{0} $
$\Rightarrow \, W_{0} =E- KE _{\max }$
$=2.56-0.38=2.18 \approx 2.16 \,eV$
Hence, the work function of cathode material is $2.16 \,eV$