A metallic plate exposed to white light emits electrons. The colour of light for which the stopping potential will be minimum is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Orange
By Einstein's photoelectric equation, the stopping potential grows linearly with the frequency of the light.
\( \displaystyle eV_0 = h\nu - \phi_0 \;\Rightarrow\; V_0 = \frac{h}{e}\,\nu - \frac{\phi_0}{e} \)
So the stopping potential is minimum for the lowest frequency, that is, the longest wavelength. In the visible spectrum the frequency increases in the order
\( \text{orange} \lt \text{green} \lt \text{blue} \lt \text{indigo} \)
Orange has the lowest frequency of the four, so it needs the smallest stopping potential. Indigo, with the highest frequency, needs the largest.
NCERT (2026-27):
Effect of Frequency of Incident Radiation on Stopping Potential – “… Above the threshold frequency, the stopping potential or equivalently the maximum kinetic energy of the emitted photoelectrons increases linearly with the frequency of the incident radiation, but is independent of its intensity (Fig. 11.5).”