Dual nature of matter and radiations


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  • Dual nature of matter and radiations

    2. 2. CONCEPTS  PHOTO ELECTRIC EFFECT – discovered by Hertz 1887. It involves conversion of light energy into electrical energy.  EINSTEIN PHOTO ELECTRIC EQUATION – PARTICLE NATURE OF LIGHT. It is in accordance with Law of conservation of energy . Max. KE = photon energy – work energy
    3. 3.  MATTER WAVES- wave energy of particles. The waves associated with the moving particles are called matter waves also called De Broglie waves .  Interference , Diffraction , and Polarization theories explain the wave nature of particles.
    4. 4. Action  PHOTO CELL – It is technological application of photoelectric effect . It converts light energy into electrical energy.  DE BROGLIE RELATION – De broglie proposed the wavelength associated with a particle of momentum P is given by  wavelenght=h/mv
    5. 5.  DAVISON AND GERMER EXPERIMENT – Wave nature of electrons was experimentally verified by Davison and Germer on 1928. They observed diffraction effect with beam of electrons scattered by a crystal. Both of them shared Nobel Prize in 1937 for their experimental discovery.
    6. 6. IMPORTANT POINTS  The minimum energy needed by an electron to come out from a metal surface is called work function of the metal .Energy (greater then the work function required for electron emission from the metal surface can be supplied by suitable heating or applying strong electric field or irradiation it by light of suitable frequency.
    7. 7.  Photoelectric effect is the phenomenon of electron by metals when illuminated by light of suitable frequency. Certain metals respond to ultraviolet light while others are sensitive even to the visible light. Photoelectric effect involves conversion of energy It follows the law of conservation of energy. The photoelectric emission is an instantaneous process and possesses certain special features.
    8. 8.      Photoelectric current depends on The intensity of incident light Photoelectric current intensity of light
    9. 9.   The potential difference applied between the two electrodesI3>I2>I1 photo I2   I3 current I1  Stopping pot.  retarding pot. Collector plate pot.
    10. 10.    Effect of frequency of incident radiation on stopping potentialphoto current Vo’> Vo’’ > Vo’’’ stopping pot  (Vo)   Vo’  retarding pot. Vo’’ Vo’’’ 0 collector plate
    11. 11.     The stopping potential (Vo) depends on – The frequency of incident light. The nature of the emitter material. The stopping potential is directly related to the max. kinetic energy of emitted of electrons emitted : eVo = 1/2mv² max= kmax Below a certain frequency , characteristic of the metal, no photoelectric emission takes place .
    12. 12.  Einstein’s photoelectric equation is in accordance with the energy conservation law as applied to the photon absorption by an electron in the metal. The max. kinetic energy (½)mv²max is equal to the photon energy (hv) minus the work function of the target metal –  ½mv²max =voe =hv =h(v-vo)
    13. 13.  The classical wave theory could not explain the main features of photoelectric effect . Its picture of continuous absorption of energy from radiation could not explain the independence of KMAX on intensity, the existence of Vo and the instantaneous nature of the process. Einstein explained these features on the basis of photon picture of light . Acc. To this , light is composed of discrete packets of energy and momentum , which depend on the frequency of incident light and not on its intensity . Photoelectric emission from the metal surface occurs due to absorption of a photon by an electron.
    14. 14.  The de Broglie wavelength associated with a moving particle is related to its momentum p as /p. The dualism of matter is inherent in the de Broglie wavelength which contains a wave concept and a particle concept. The de Broglie wavelength is independent of the charge and the nature of the material particle.
    15. 15.  Electron diffraction experiments by Davisson and Germer , and by G.P . Thomson , as well as many experiments , have verified and confirmed the wave nature of electrons. The de Broglie hypothesis of matter waves supports the Bohr’s concepts of stationary orbits.