Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): For a given emitter, the stopping potential becomes larger when the frequency of the incident light is increased.
Reason (R): For light of a given frequency, the stopping potential depends on the nature of the emitter material.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
Assertion (A) For a given emitter, the stopping potential becomes larger when the frequency of the incident light is increased. — True. Light of higher frequency gives photoelectrons of larger maximum kinetic energy. A larger retarding potential is then needed to stop them.
Reason (R) For light of a given frequency, the stopping potential depends on the nature of the emitter material. — True. Different metals have different work functions. So the same light gives photoelectrons of different maximum kinetic energy from different metals, and the stopping potential is different.
Why Reason (R) does not explain Assertion (A)?
R compares different emitters lit by light of one frequency. A is about one emitter when the frequency changes.
For one emitter, the work function \( \phi_0 \) is fixed. From \( eV_0=h\nu-\phi_0 \), the stopping potential grows when \( \nu \) grows, and that is the reason for (A).
NCERT (2026-27):
Effect of frequency of incident radiation on stopping potential – “… This implies that greater the frequency of incident light, greater is the maximum kinetic energy of the photoelectrons. Consequently, we need greater retarding potential to stop them completely.”
Summary – “4. The stopping potential (Vo) depends on (i) the frequency of incident light, and (ii) the nature of the emitter material. …”