Assertion (A): When the intensity of light of a fixed frequency falling on a photosensitive surface is increased, the maximum kinetic energy of the emitted photoelectrons does not change. Reason (R): The number of photoelectrons emitted per second is directly proportional to the intensity of the incident light.
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Both statements are experimental facts: the stopping potential, and hence K_max, is independent of intensity, while the photocurrent grows in proportion to intensity. A holds because K_max = hν − φ₀ depends only on the frequency of the light, which R does not mention, so R does not explain A.
- A.
R explains why the photocurrent rises with intensity, not why K_max stays the same; that follows from K_max = hν − φ₀.
- C.
R is true: the saturation current is proportional to intensity.
- D.
A is true: the stopping potential does not change with intensity.
NCERT: Class 12 Physics, Chapter 11 (Dual Nature of Radiation and Matter), Experimental study of photoelectric effect