Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): For light of a given frequency above the threshold frequency, the photoelectric current is proportional to the intensity of the light.
Reason (R): At a given frequency, light of greater intensity has more photons falling on the surface per second, so more electrons absorb a photon and come out of the metal per second.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
Assertion (A) For light of a given frequency above the threshold frequency, the photoelectric current is proportional to the intensity of the light. — True. Keeping the frequency and the collector potential fixed, the photocurrent is found to rise linearly as the intensity is increased.
Reason (R) At a given frequency, light of greater intensity has more photons falling on the surface per second, so more electrons absorb a photon and come out of the metal per second. — True. In the photon picture, all photons of one frequency carry the same energy \( h\nu \). So a brighter beam of that light only has more of these photons arriving every second. For \( \nu\gt\nu_0 \), an electron that absorbs one photon can escape, and more photons mean more emitted electrons.
Why R explains A?
The photocurrent is proportional to the number of photoelectrons emitted per second.
R ties that number to the number of photons arriving per second, which is what the intensity measures at a fixed frequency. So the current is proportional to the intensity, as stated in A.
NCERT (2026-27):
Einstein’s Photoelectric Equation: Energy Quantum of Radiation – “… In this picture, intensity of radiation as noted above, is proportional to the number of energy quanta per unit area per unit time. The greater the number of energy quanta available, the greater is the number of electrons absorbing the energy quanta and greater, therefore, is the number of electrons coming out of the metal (for ν > ν0). This explains why, for ν > ν0, photoelectric current is proportional to intensity.”