Ultraviolet light of wavelength 280 nm is used in an experiment on photoelectric effect with lithium whose work function is 2.5 eV as cathode. The stopping potential is (approximately)
(Take Planck's constant h and velocity of light c) and hc = 1242 eVnm
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 1.94\,\mathrm{V} \)
By Einstein's photoelectric equation, the energy of a photon minus the work function is the maximum kinetic energy of the photoelectrons, which equals \( eV_0 \).
\( \displaystyle eV_0 = \frac{hc}{\lambda} - \phi_0 \)
\( \displaystyle \frac{hc}{\lambda} = \frac{1242\,\mathrm{eV\,nm}}{280\,\mathrm{nm}} = 4.436\,\mathrm{eV} \)
\( eV_0 = 4.436 - 2.5 = 1.936\,\mathrm{eV} \)
\( V_0 \approx 1.94\,\mathrm{V} \)