# Photoelectric Effect and Einstein's Photoelectric Equation

Photoelectric Effect
=Electromagnet radiation can push electron free from the surface of a solid.
*This process is called the photoelectric effect .
*A material that can exhibit the photoelectric effect is said to be photomassive  .
*Electron ejected by the photoelectric effect are called Photo-electrons.

=The Photoelectric effect will not occur when the frequency of the incidents light is less than the threshold frequency.
*Different materials have different threshold frequency .
*Most elements have threshold frequency in the ultraviolet region of the electromagnet spectrum.

=The maximum kinetic energy of a stream of photo-electrons.....
*is determined by measuring the stooping potential .
*increase linearly with the frequency of the incident light above the threshold frequency.
*is independent of the intensity of the incident light.

=The rate at which photo-electrons are emitted from a Photoemissive  surface.
*is determined by measuring the electric current .
* is directly proportional to the intensity of the incident light when frequency is constant .

=On graph of maximum kinetic energy vs frequency.....
*all curves are linear with slope equal to the plank's constant.
*the intercept on the energy axis is the threshold frequency of the material .

=Classical physics cannot explain why .....
*no photo-electrons are emitted when the incident light has a frequency below the threshold .
*the maximum kinetic energy of the photo-electrons is independent of the intensity of the incident light and ,
*there is essential no delay between absorption of the radiant energy and the emission of photo-electrons .

=Modern Physics states that....
*electromagnetic radiation is composed of discrete entities called photons .
*the energy of a photon is proportional to its frequency .
*the work function of a material of a material is energy needed per photon to extract an electron from its surface.

Equations
* Photoelectric effect
Kmax = h(f - f o)

*Photon energy
E= hf =hc/λ

*Work function
hfo=hc/λo

* Stopping potential
Kmax =evo

Note:-  The term photoelectric effect in science is a phenomenon in which a ray/rays of light /lights fall on a pool of electron gets energized and leves the surface of that metal.

Einstein's Photoelectric Equation

=Einstein argued that light was a wave that interats with matter in the form of  a packets of energy or a quantum of energy. This quantum of radiation was a photon and the equation was called Einstein 's Photoelectric equation .
=He assumed that kinetic energy of the ejected electron was equal to the energy of the incidents photon minus the energy required to remove the electron from the materials , which is called work function .
=the energy of photon is given by E= hg= hc/I where g is the frequency of the photon
where,
h=Plank's constant
c =velocity of light
I= wavelength