Question
A ray of light with wavelength $\lambda$ is incident on three different photoelectric cells namely 1, 2 and 3. The threshold wavelength of these photoelectric cells are $\lambda_{1},\lambda_{2}$, and $\lambda_{3}$, respectively and the magnitude of stopping potentials of these cells are $V_{1},V_{2}$ and $V_{3}$, respectively. The relation between $\lambda$ and threshold wavelengths are $\lambda_{1} < \lambda,\lambda_{2} > \lambda$ and $\lambda_{3} \gg \lambda$. The correct option is:
Options
Solution
Sol. [Key Concept: Photoelectric threshold and stopping potential]
For ejection of electron energy of incident photon should be greater than work function
$${\begin{matrix} \phi & \ = \frac{hc}{\lambda} \\ \phi_{1} & \ = \frac{hc}{\lambda_{1}} \\ \lambda_{1} & \ < \lambda \\ \phi_{1} & \ > \phi \end{matrix} } {No\ electron\ will\ eject } {V_{1} = 0 } {By\ Einstein\ photoelectric\ equation } {\begin{matrix} & \phi = \phi_{0} + eV \\ & \lambda_{2} > \lambda \\ & \lambda_{3} \gg \lambda \\ & \phi > \phi_{2} \\ & \phi \gg \phi_{3} \end{matrix} } {So,\ V_{3} > V_{2}}$$
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