Answer:
The photoelectric effect occurs only for frequencies above the cutoff frequency, regardless of the intensity.
Explanation:
The photoelectric effect occurs when light is shined on metals such as zinc beyond a certain frequency (the threshold frequency), which causes electrons to escape from the zinc. The electrons which are fleeing are called photo electrons.
Therefore photo electric effect is
The photoelectric effect occurs only for frequencies above the cutoff frequency, regardless of the intensity.
It took so long because at the time there was no way for people to study the behavior formally. im not sure what helped it get recognized but i know wihelm wundt helped get it recongnized.
sorry i couldnt be much help