Does the intensity of light mean increase no. of photons?
For a given frequency of photons it does. A maximum of one photoelectron for each arriving photon.
Then for instance if the light carries 21 photons per second then the next second also should carry the same amount of photons
The equivalence is only there for statistically large numbers. You would not get 21 every second.
Thanks for the information
Oh, if only! The statistical fluctuation in photons per unit of time is known as "Shot Noise" and is a major source of noise in photometry, astrophotography, and other areas.
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