1 / 30

Interference and Diffraction

Light's Nature. Wave nature (electromagnetic wave)Particle nature (bundles of energy called photons). Past- Separate Theories of Either Wave or Particle Nature. Corpuscular theory of Newton (1670) Light corpuscles have mass and travel at extremely high speeds in straight lines Huygens (1680) W

norm
Download Presentation

Interference and Diffraction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. Interference and Diffraction Physics Mrs. Coyle

    2. Light’s Nature Wave nature (electromagnetic wave) Particle nature (bundles of energy called photons)

    3. Past- Separate Theories of Either Wave or Particle Nature Corpuscular theory of Newton (1670) Light corpuscles have mass and travel at extremely high speeds in straight lines Huygens (1680) Wavelets-each point on a wavefront acts as a source for the next wavefront   

    4. Why was it difficult to prove the wave part of the nature of light?

    5. Proofs of Wave Nature Thomas Young's Double Slit Experiment (1807) bright (constructive) and dark (destructive) fringes seen on screen Thin Film Interference Patterns Poisson/Arago Spot (1820) Diffraction fringes seen within and around a small obstacle or through a narrow opening

    6. Proof of Particle Nature: The Photoelectric Effect Albert Einstein 1905 Light energy is quantized Photon is a quantum or packet of energy

    7. The Photoelectric Effect Heinrich Hertz first observed the photoelectric effect in 1887 Einstein explained it in 1905 and won the Nobel prize for this.

    8. Thomas Young’s Double Slit Interference Experiment Showed an interference pattern Measured the wavelength of the light

    9. Two Waves Interfering

    10. Young’s Double Slit Interference Pattern

    12. Interference of Waves From Two Sources Simulation “Ripple Tank” http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320005/simulations6e/index.htm?newwindow=true

    13. Interference Young’s Double Slit Interference http://galileo.phys.virginia.edu/classes/109N/more_stuff/flashlets/youngexpt4.htm

    14. For Constructive Interference: The waves must arrive to the point of study in phase. So their path difference must be integral multiples of the wavelength: DL= nl n=0,1,2,3,………

    15. For destructive interference: , the waves must arrive to the point of study out of phase. So the path difference must be an odd multiple of l/2: DL= n l m=1/2,3/2,5/2,….

    16. Typical Question Where is the first location of constructive or destructive interference?

    17. Fo Constructive Interference of Waves from Two Sources

    18. Double Slit Interference dsinq=nl nl = dx L Constructive (brights) n=0,1,2,3,….. Destructive (darks) n=1/2, 3/2, 5/2,….. Note: To find maximum # of fringes set q to 90o for n.

    19. Question How does x change with wavelength? How does x change with slit distance?

    20. Problem Two slits are 0.05 m apart. A laser of wavelength 633nm is incident to the slits. A screen is placed 2m from the slits. a) Calculate the position of the first and second bright fringe. b) What is the maximum number of destructive interference spots there can be on either side of the central maximum?

    21. Diffraction Grating

    22. Diffraction Grating Large number of equally spaced parallel slits. Equations are same as for double slit interference but first calculate the d (slit separation) from the grating density, N. d=1/N , N slits per unit length dsinq=nl nl = dx L Constructive (brights) n=0,1,2,3,….. Destructive (darks) n=1/2, 3/2, 5/2,…..

    23. Problem A neon laser of wavelength 633nm is pointed at a diffraction grating of 3000lines/cm. Find the angle where the first bright occurs. (Hint: slit separation d is inverse of grating density)

    24. Diffraction Wave bends as it passes an obstacle.

    25. Diffraction through a Narrow Slit Each part of the slit acts as a point source that interferes with the others. (Based on Huygens Principle)

    26. Pattern of Diffraction of Light through a Narrow Slit

    27. Intensity of the Diffraction Interference Patterns Simulation “Interference of Light” http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320005/simulations6e/index.htm?newwindow=true

    28. Diffraction from Narrow Slit wsinq=nl l= nw y L w: is the width of the slit Destructive (dark fringes): m=0,1,2,3,….

    29. Questions How does x change with the width? How does x change with the wavelength

    30. Diffraction around a Penny and Poison Spot

    31. Example of Diffraction

More Related