Question

A polychromatic light is used in an experiment on photoelectric effect. The stopping potential:
A. Is related to the mean wavelength
B. Is related to the longest wavelength
C. Is related to the shortest wavelength
D. Is not related to the wavelength.

Answer 1

The stopping potential is the potential needed to stop the electrons having maximum kinetic energy in the photoelectric effect. A wave with the maximum frequency will emit the maximum kinetic energy of an electron. We know that it is inversely related to frequency and wavelength. We can arrive at the correct answer using this relationship.

Complete solution :
When light radiation falls on it the photoelectric effect is the ejection of electrons from a metal surface. For the removal of an electron from the surface, the energy of the incoming photon is used and additional energy is converted into the electron's kinetic energy.

Therefore, if a photon has greater energy, then the kinetic energy of the emitted electron will be greater. Since non-monochromatic light is used the electron with the maximum kinetic energy will generate the maximum frequency of the light component.

The stopping potential ($V_s$) in photoelectric effect related with the incident light frequency $(v)$ by the following equation:
$\mathrm{eV}_{\mathrm{s}}=\mathrm{h} v-\phi$

where $\phi$ is the work function of the material So, the stopping potential is related to the shortest wavelength or longest frequency So, the answer is option (C).

Note:
Remember that wavelength is inversely related to frequency. A higher frequency wave will have greater energy. So for the maximum frequency, the kinetic energy of the emitted electrons will be the maximum. There will be a minimum wavelength when the frequency is the maximum. The stopping potential in the photoelectric effect is the potential required to stop the electrons having the maximum kinetic energy.