What photo electric effect?. It can be defined as the emission of electron from metalsurface when photon or electromagnetic radiation fall on it shows on it. For some surface like sodium, the wavelength photons have to be short (ultra-violent or x-ray). To ensure emission. While for other such as cesium electrons were emitted when photon of long wavelength (infra-red radiation) fall on it. The photo electric effect was first observed by Hertzin 1887.
The number of photo electrons emitted is directly proportional to the intensity of the radiation
The energy of emitted electrons depend on the frequency of the incident radiation
There exists the threshold frequency for all surface , and below the frequency no electron is emitted , no matter the intensity of the radiation, so as long as the radiation with frequency above the threshold value is used the emission is instantaneous
No electron is emitted from the positive plate, due to mutual attractive force between electrons and the plate.
Demonstration of photo electric effect.
Electrons emitted from the cathode are pushed toward the Anode by electric field force. If the direction ofelectric field is reversed, some electrons will still reach the anode. The kinetic energy of emitted electron at anode is zero, and have a potential energy of eVo ( Stopping potential).