IB DP Physics: HL复习笔记9.3.3 Diffraction Grating Patterns

Diffraction Grating Patterns

  • A diffraction grating is a plate consisting of a very large number of parallel, identical, close-spaced slits
    • When monochromatic light is incident on a grating, a pattern of narrow bright fringes is produced on a screen

8.2.3.1-Diffraction-grating-diagram

 

Diffraction grating with multiple slits, usually described in terms of 'slits per metre'

  • The number of slits dictates both the interference and diffraction patterns which are seen
  • On the screen a diffraction pattern is observed
    • The interference pattern is a measure of the intensity of the light at different angles of diffraction away from the central maxima
    • For a double slit arrangement this is shown in (9.3.2 Two-Slit Interference Patterns)
  • On the diffraction pattern as the number of slits increases:
    • Between the maxima, secondary maxima appear
    • The central maxima and subsequent bright fringes become narrower

9-3-3-multiple-slit-diffraction

Diffraction patterns for light interfering through different numbers of slits

  • When there are 3 slits, 1 secondary maxima can be seen between the primary maxima
  • When there are 5 slits, 3 secondary maxima can be seen between the primary maxima
    • Therefore, with N slits (when N > 2), there are (N − 2) secondary maxima
  • Once the number of slits increases to N > 20:
    • The primary maxima will become thinner and sharper (since slit width,