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Explain the photoelectric effect . |
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Answer» Solution :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 oneelectron ) and`hupsilon_(0)` i.e., `hupsilon=hupsilon_(0)+(1)/(2)mv^(2)` |
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