Photoelectric Effect

Electrons
Electrons are the sub atomic particles of an atom, which are negatively charged. According to Bohr's Atomic Model, electrons revolve around the nucleus in stationary orbits at specific energy levels. When an electron absorbs energy, its energy level increases and it jumps out of the orbit and moves away from the nucleus.

Energy
According to Planck's Quantum Theory, Energy exists in the form of discrete packets or bundles known as Quanta. Whenever an electron absorbs a quanta, its energy increases ; the electron jumps to a higher energy level and thus , it moves away from the nucleus.

Photon
Photon is a type of Quanta. Photons are discrete packets of light energy. The word "Quanta" is used for all forms of energy, while the word "Photon" is used for only light energy. Photons have the same effect on electron as Quanta has.

Photoelectric Emission
As we have learnt earlier in this chapter, electrons move away from the nucleus when electron is provided with energy. When light of a certain energy is incident on a metal surface, electrons are emitted out due to absorption of energy by it. This phenomenon is called as photoelectric emission. The surface from which electrons are emitted is said to be "photosensitive". Alkali Metals are highly photosensitive. The electrons emitted in the process are called as photoelectrons. Light of a certain frequency or wavelength is needed to produce a light of minimum energy needed to produce photoelectric effect.

Work Function
The minimum energy needed to produce photoelectric effect is called as Work Function. The work done by this energy is in breaking the bonding of the electron with its nucleus and the metal surface .It can also be defined as the bond strength of electron with its metal surface.

The work function for a substance with incident light should be close or less than 2.3 eV.

Intensity & Frequency
The number of photo electrons emitted depends upon the intensity of light incident on it. The kinetic energy of the photo electrons emitted depends upon the frequency of light incident on it.

Stopping Potential
Note :

When the distance of radiation is changed, stopping potential remains same , while current changes due to change in intensity.

Intensity is inversely proportional to the square of distance of radiation. This relation can be used to find saturation current.