Write the characteristics of the photoelectric effect.

(N/A) $(i)$ For a given photosensitive substance, when the frequency of incident radiation is greater than the threshold frequency, the photoelectric current is directly proportional to the intensity of light.
$(ii)$ For a given photosensitive substance and frequency of incident radiation, the saturation current is proportional to the intensity of radiation, but the stopping potential is independent of the intensity.
$(iii)$ For a given photosensitive substance, if the frequency is less than the threshold frequency, photoelectric emission will not take place, regardless of the intensity of radiation.
$(iv)$ For a frequency greater than the threshold frequency $(v > v_{0})$, the stopping potential and maximum kinetic energy vary linearly with the frequency of the incident radiation, but they do not depend on the intensity of the radiation.
$(v)$ Photoelectric emission is an instantaneous process, occurring within a time interval of $10^{-9} \,s$ or less.