Photoelectrons are emitted from a photosensitive surface for the light of wavelengths $\lambda_{1}=360…

Photoelectrons are emitted from a photosensitive surface for the light of wavelengths $\lambda_{1}=360 \mathrm{~nm}$ and $\lambda_{2}=600 \mathrm{~nm} .$ What is the ratio of work functions for lights of wavelength ${ }^{\prime} \lambda_{1}{ }^{\prime}$ to $\lambda_{2}{ }^{\prime}$?
  1. $6: 1$
  2. $1: 6$
  3. $5: 3$
  4. $3: 5$

Solution

$\frac{h c}{\lambda_{1}}-\phi_{1}=\mathrm{KE} \quad \quad \lambda_{1}=360 \mathrm{~nm}=360 \times 10^{-9} \mathrm{~m}$ $\frac{\mathrm{hc}}{\lambda_{2}}-\phi_{2}=\mathrm{KE} \quad \quad\lambda_{2}=600 \mathrm{~nm}=600 \times 10^{-9} \mathrm{~m}$ $\frac{h c}{\lambda_{1}}=\phi_{1} \quad \quad \phi \propto \frac{1}{\lambda}$ $\therefore \frac{\phi_{1}}{\phi_{2}}=\frac{\lambda_{2}}{\lambda_{1}}=\frac{600}{360}=\frac{10}{6}=\frac{5}{3}$

Asked in: MHT CET 2020 (20 Oct Shift 2)

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