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# photo electric effect slides

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### Transcript

1. Izhar Ullah (Reg#CSEE-XF12-200)
2. OUTLINE: Introduction.  Laws of Photo Electric Effect.   EINSTEIN’S EQUATION.  APPLICATION.
3. INTRODUCTION: First observed by Heinrich Hertz in 1887, the phenomenon is also known as the Hertz effect.  Hertz observed and then showed that electrodes illuminated with ultraviolet light create electric sparks more easily. 
4. The ejection of electrons from a metallic surface when the light of suitable frequency is allowed to fall on the surface.
5. • This suitable frequency is called Threshold Frequency and the corresponding wavelength is called threshold wavelength. • 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.
6. • Photoelectric effect is directly proportional to intensity. • If the frequency of the incident light is less than the threshold frequency then no electron ejected, no matter what the intensity. • The maximum kinetic energy of the electrons depend on the frequency of the incident light. • The electrons were emitted immediately - no time lag.
7. EINSTEIN’S EQUATIONS FOR THE PHOTOELECTRIC EFFECT Einstein's interpretation of the photoelectric effect results in equations which are valid for visible and ultraviolet light: energy of photon = energy needed to remove an electron + kinetic energy of the emitted electron  hν = W + E Where  h is Planck's constant ν is the frequency of the incident photon W is the work function, which is the minimum energy required to remove an electron from the surface of a given metal: hν0 E is the maximum kinetic energy of ejected electrons: 1/2 mv2 ν0 is the threshold frequency for the photoelectric effect m is the rest mass of the ejected electron v is the speed of the ejected electron
8. EINSTEIN’S EQUATIONS FOR THE PHOTOELECTRIC EFFECT :  No electron will be emitted if the incident photon's energy is less than the work function.
9. Km:- maximum kinetic energy E :- energy of photon’s W :- work function of metal
10. WORK FUNCTIONS OF SELECTED METALS Metal Ø (eV) Na 2.46 Al 4.08 Cu 4.70 Zn 4.31 Ag 4.73 Pt 6.35 Pb 4.14 Fe 4.50
11. APPLICATION OF PHOTO ELECTRIC EFFECT:  Television Camera Tubes  Light-Activated Counters  Automatic Doors  Intrusion Alarms  Turn on Street Lights at Dawn