IB Physics Diffraction

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This tutorial sheet is about diffraction, a concept that is not widely understood.

  1. State the definition of diffraction.
  2. Why does diffraction occur when light passes through a single slit?
  3. Explain qualitatively the pattern that we see when light passes through a single slit if i. the slit width is much greater than the wavelength ii. the slit width is much less than the wavelength.
  4. Divide a single slit of width b into two sections. By considering a ray from the top of each section, show that destructive interference occurs when b sin๐œƒ = ๐œ†. Do this with four sections in the slit and show that destructive interference occurs when b sin๐œƒ = 2๐œ†. This can be generalized to b sin๐œƒ = n๐œ†, n=1,2,..
  5. When light is now incident normally on a diffraction grating what does the equation d sin๐œƒ = n๐œ†, n=0,1,2,3.. predict?
  6. The incident monochromatic light is not normal to the grating. Can we use the equation d sin๐œƒ = n๐œ† in this situation?
  7. In question 6 the angle of incidence of the light on the grating is ฯ•. Show that the angle ๐œƒ to the normal to the grating where intensity maxima occur are given by d ( sin(๐œƒ - ฯ•) - sinฯ• ) = n๐œ†.
  8. Describe the difference between primary maxima and secondary maxima.
  9. Describe the interference pattern when white light is incident normally on a diffraction grating.