Explain the photoelectric effect .

Explanation

Photoelectric effect : J.J Thomson and P . Lenard showed that "when a beam of light of suitable wavelength is allowed to fall on the surface of a metal , the electrons are emitted from the surface of the metal". This phenomenon is called , photoelectric effect.
Explanation of photoelectric effect by Einstein : Einstein (1905) explained photoelectric effect with the help of Planck's quantum theory of radiation.
According to quantum theory of radiation , a photon of light of frequency , `upsilon` is as-sociated with energy equal to `upsilon` . When a photon of light frequency `upsilon(upsilon` is higher than threshold frequency ) falls on a metal some of the energy associated with the photon is consumed to separate the electron from the surface and the remaining energy is imparted to the ejected electron , to given it certain velocity , say equal to v . Due to this velocity , the emitted electron gains kinetic energy to `(1)/(2)mv^(2)` . The proton of energy which is consumed to separate the electron is equal to the binding energy of the electron . This energy is called 'thresh-old energy' or ' work function ' and is equal to the product of h and threshold frequency `(upsilon_(0))` of a photon of radiation falling on the metal surface . Thus this energy is equal to `(hupsilon_(0))` . This above discussion shows that `hupsilon` is equal to the sum of `(1)/(2)mv^(2)` (K.E. of one electron ) and `hupsilon_(0)`
i.e., `hupsilon=hupsilon_(0)+(1)/(2)mv^(2)`