Choose the correct statement(s)
A. In photo electric effect, the minimum negative potential to the plate A for which photocurrent is zero is called saturation potential.
B. Maximum kinetic energy of photoelectrons is directly proportional to intensity of incident radiation.
C. \( K_{max} = eV_o \).
D. Photocurrent becomes zero at stopping potential.
E. For different intensities of light, stopping potential is different.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → C & D only
The stopping potential \( V_0 \) is the negative plate potential that just stops the fastest photoelectrons. By Einstein's photoelectric equation:
\( \displaystyle K_{\max} = eV_0 = h\nu - \phi_0 \)
(A) In photo electric effect, the minimum negative potential to the plate A for which photocurrent is zero is called saturation potential. — Incorrect. This potential is the stopping (cut-off) potential. The saturation current is reached at large positive plate potentials.
(B) Maximum kinetic energy of photoelectrons is directly proportional to intensity of incident radiation. — Incorrect. \( K_{\max} = h\nu - \phi_0 \) does not contain the intensity; a higher intensity gives more photoelectrons, not faster ones.
(C) \( K_{max} = eV_o \). — Correct. At the stopping potential the work \( eV_0 \) done against the field just uses up the largest kinetic energy.
(D) Photocurrent becomes zero at stopping potential. — Correct. This is the definition of the stopping potential: even the fastest electrons can no longer reach the plate.
(E) For different intensities of light, stopping potential is different. — Incorrect. For a given frequency \( V_0 \) is the same for every intensity, because \( K_{\max} \) does not depend on intensity.
NCERT (2026-27):
Effect of Potential on Photoelectric Current – “… For a particular frequency of incident radiation, the minimum negative (retarding) potential V0 given to the plate A for which the photocurrent stops or becomes zero is called the cut-off or stopping potential. … Photoelectric current is zero when the stopping potential is sufficient to repel even the most energetic photoelectrons, with the maximum kinetic energy (Kmax), so that
\( \displaystyle K_{max} = e\,V_0 \qquad (11.1) \)”
Effect of Potential on Photoelectric Current – “… Thus, for a given frequency of the incident radiation, the stopping potential is independent of its intensity. In other words, the maximum kinetic energy of photoelectrons depends on the light source and the emitter plate material, but is independent of intensity of incident radiation.”