Question

Light of wavelength $488nm$ 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 $0.38V$. 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, $\lambda =488nm$ and stopping potential, of photoelectrons, $V=0.38V$
As, energy of photon
$E=\frac{hc}{\lambda }=\frac{1250}{488}eV$
So, $E=2\cdot 56eV$
$\because$ Maximum kinetic energy of a photo-electron
$K{E}_{\max }=e{V}_0$
Where, $V_0=$ stopping potential
$\therefore K{E}_{\max }=e{V}_0=0.38eV$
From Einstein's photoelectric equation,
$E=K{E}_{\max }+W_0$
$\Rightarrow W_0=E-K{E}_{\max }$
$=2.56-0.38=2.18\approx 2.16eV$
Hence, the work function of cathode material is $2.16eV$