Write any three experimental observations of photoelectric effect

Explanation

(i) The photoelectric emission is an instantaneous process without any apparent time lag (`~10^(-9)` s or less), even when the incident radiation is made exceeding by dim.
(ii) For every photo emissive surface there is a certain minimum frequency of the incident radiation below which there is no photoelectric effect, called threshold frequency and the corresponding wavelength is called threshold wavelength no matter how intense the incident light is. Threshold frequency is different for different materials.
(iii) For a frequency greater than the threshold frequency, the strength of the photoelectric current is directly proportional to the intensity of the incident radiation.