In the wave picture of light, the intensity of light is determined by the square of the amplitude of the wave. What determines the intensity of light in the photon picture of light for a given frequency?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The number of photons crossing a unit area per unit time.
In the photon picture, light of frequency \( \nu \) is a stream of photons, each carrying energy \( h\nu \). Intensity is energy crossing unit area in unit time, so for a fixed frequency it is set by the number of photons crossing unit area per unit time (the photon flux).
\( I = (\text{photon flux})\times h\nu \)
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