Why kinetic energy of photoelectrons rise up to a maximum?
That question does not make sense.
If you ask why it has a maximum: energy conservation. You cannot create energy.
What you have asked is what I understood but this question is from an actual advanced physics exam taken in the past. So why does it have maximum?
I doubt that what you have written was the whole of the question. There must be some context if you need a proper answer.
Energy conservation always applies.
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