Write three experimental observation of photoelectric effect.

Explanation

1. The photoelectric effect is instantaneous. i.e., photoelectric current flows as soon as the radiation falls on the cathode (about `10^(-9)S)`.
2. The strength of photo electric current is directly proportional to the intensity of incident radiation.
3. For a given photo emissive surface there is a minimum frequency for the incident radiation below which there is no photoelectric emission. This minimum frequency is called threshold frequency.
4. Above threshold frequency, the maximum kinetic energy of the photoelectrons increases linearly with the frequency of the incident radiation.
5. As the applied potential is increased the photoelectric current increases and attains saturation. On reversing the potential, photo current decreases and becomes zero at a particular negative potential and is called stopping potential `V_(s)`.