Photo electric effect


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Photo electric effect

  1. 1. The Photo Electric Effects<br />By :- <br />Nikhil Merothiya<br />
  2. 2. We know that the light has dual nature.<br />The Phenomena of interference & diffraction etc. can be explained on the basis of wave theory of light.<br />Whereas the phenomena of Photoelectric Effect , compton effect can be explained on the basis of particle theory of light.<br />
  3. 3. The Photo Electric Effect<br />The ejection of electrons from a metallic surface when the light of suitable frequency is allowed to fall on the surface.<br />
  4. 4. The Photo Electric Effect<br />This suitable frequency is called Threshold Frequency and the corresponding wavelength is called threshold wavelength.<br />Work function: The work function is the energy required to remove an electron from the highest filled level in the Fermi distribution of a solid. <br />
  5. 5. Typical Experimental Setup<br />
  6. 6. • Incident light triggers the emission of (photo)electrons from the cathode.<br />• Some of them travel toward the collector (anode) with an initial kinetic energy.<br />• The applied voltage V either accelerates (if positive) or decelerates (if negative) the incoming electrons.<br />•The intensity I of the current measured by the ammeter as a function of the applied voltage V is a measurement of the photoelectron properties, and therefore a measurement of the properties of the photoelectric effect.<br />
  7. 7. How to understand the Photoelectric Effect?<br />Think about hitting a ball into outer space.<br />If you don't hit it hard enough, it will just come back down. No matter how many times you hit it.<br />If superman hit it, he could get it into space.<br />Similarly, no matter how many photons strike the metal, if none of them has sufficient energy to eject an electron from a metal atom, you won't get a current.<br />If the energy the taken up by the electron is sufficient to allow it to be released from the metal atom, you will get a current.<br />
  8. 8. Relation between energy of photon & emitted electron’s maximum kinetic energy<br />Km<br />Km :- maximum kinetic energy of emitted electron<br />W :- work function<br />E<br />W<br />
  9. 9. Relation between current & applied potential difference<br />V :- potential difference<br />Vs :- stopping potential<br />ʋ :- frequency (constant)<br />V<br />
  10. 10. Relation between current & frequency<br />The stopping potential depends on the frequency:-Higher frequencies generates higher energy electrons.<br />Ʋ1 > Ʋ2 > Ʋ3<br />Ʋ1<br />Ʋ2<br />Ʋ3<br />Vs1<br />Vs2<br />Vs3<br />
  11. 11. Laws of Photoelectric effect<br />Photoelectric effect is directly proportional to intensity.<br /> If the frequency of the incident light is less than the threshold frequency then no electron ejected, no matter what the intensity.<br /> The maximum kinetic energy of the electrons depend on the frequency of the incident light.<br />The electrons were emitted immediately - no time lag.<br />
  12. 12. Einstein’s equation<br />Km = E - W <br />Km:- maximumkinetic energy<br />E :- energy of photon’s<br />W :- work function of metal<br />
  13. 13. Einstein’s equation<br />m = tan θ<br />Km<br />E<br />W<br />
  14. 14. Use of Photoelectric effect<br />Photo cell<br />
  15. 15. THANKING YOU<br />