The longest wavelength of light that can cause emission of electrons from a photosensitive material of work function 2.2 eV will be
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 564 nm
Electrons are emitted only if the photon energy is at least the work function. The longest wavelength that can do this is the threshold wavelength, for which the photon energy just equals the work function.
\( \displaystyle \frac{hc}{\lambda_0} = \phi_0 \)
\( \displaystyle \lambda_0 = \frac{hc}{\phi_0} \)
Using \( hc \approx 1240\,\mathrm{eV\,nm} \):
\( \displaystyle \lambda_0 = \frac{1240\,\mathrm{eV\,nm}}{2.2\,\mathrm{eV}} \)
\( \displaystyle \lambda_0 \approx 564\,\mathrm{nm} \)