Quantum Phenomena

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  • Created by: Murray_R
  • Created on: 15-12-13 17:11

Photo Electricity

  • photoelectric emission of electrind from a metal surface does not take place below the threshold frequency which depends on the metal
  • the number of electrons emmitted per second is proportinal to the intensity of the light if the frequency is above the threshold frequency
  • photo electric emission occurs without delay (this is an assumption)
  • when light is incident in a metal surface a electron at the surface gains a singl ephoton and gains energy equal to hf
  • an electron can leave the surface if it gains more energy than the work function 0(the minimum energy needed by an electron to be liberated from the metal surface)

energy of a photon=hf
E=hf=hc/λ

EKMAX =hf-0
hf=EKMAX +0
FMIN =0/h

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More About Photoelectricity

  • the work functiton of the metal is the minimu energy needed by a conducting electron to escape from the metal surface when a metal is at zero potential

The Vacuum Photocell

  • this is a glass tube which contains a metal plate (photocathode) and a smaller metal electrode (anode)
  • nuber of photoelectrons transfered from the cathode to the anode=I/e (e=charge of the electron)
  • the current is proportinal to the intensity of the light
  • the intensity does not efect the maxium kinetic energy of an electron emmitted
  • if the measurements are plotted on a graph of y=mx+c where Y=Ek and X=f the gradient(m)=H/Plancks constant the Y intercept will be the -0 (work function and the Xintercept will equal the thresehold frequency
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Collision of Electrons With Atoms

  • any processe produceing ions is called ionising (alpha beta gamma radioation and electrons in a fluorecent tube)
  • electron volt to joules=  1.6x10-19
  • joules to electron volt=   1.6x10-19
  • when a photon or electron hits an electron in an atom it excited the electron so it move energy levels away for the ground state
  • when an elec tron de-excites it moves down energy levels towards the ground state and releases a photon 
    Emitted Photons Energy=E1-E2 
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Fluorescence

  • a Fluorescence tube is a tube with a Fluorescent coating in the inner surface it contains murcury vapour at a low pressurewhen it is on visible light is emmitted because
    1)ionisation and excitation of the murcury atoms occures as the collide with each other and elactron in the tube
    2)the mercury atoms emit ultra-violet photons aswell as visible light
    3)the ultraviolet photons are absorbed by the atoms in the coating causeing excitation in the atoms
    4)the coating de-excites and emmits visable photons
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Energy Levels And Spectra

  • Line spectrums
    each line is due to light of a certain colour and therefore o certain wavelenghts
    the photons that produce each line energy is diferent to the photon that produces any other line
    each photon is emmitted when an electron de-excites
  • the difference between a line and continuous spectrum a line spectrum shows discrete lines which correspond to descreet energy levels where as the continuos spectrum show a spread of colours
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Wave Particle Duality

Light

  • Wave Like behaviour=defraction
    Particle like behaviour=Photoelectriv effect

Matter

  • Wave like behaviour=de broglie wavelenght
    particle like behaviour=conservation of momentu laws,collision with atoms
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Wave Particle Duality

Light

  • Wave Like behaviour=defraction
    Particle like behaviour=Photoelectriv effect

Matter

  • Wave like behaviour=de broglie wavelenght
    particle like behaviour=conservation of momentu laws,collision with atoms
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