Understandings: Young’s double-slit experiment, Modulation of two-slit interference pattern by one-slit diffraction effect, Multiple slit and diffraction grating interference patterns, Thin film interference
Applications and skills: Qualitatively describing two-slit interference patterns, including modulation by one-slit diffraction effect, Investigating Young’s double-slit experimentally, Sketching and interpreting intensity graphs of double-slit interference patterns, Solving problems involving the diffraction grating equation, Describing conditions necessary for constructive and destructive interference from thin films, including phase change at interface and effect of refractive index, Solving problems involving interference from thin films
Utilization: Compact discs are a commercial example of the use of diffraction gratings, Thin films are used to produce anti-reflection coatings
Guidance: Students should be introduced to interference patterns from a variety of coherent sources such as (but not limited to) electromagnetic waves, sound and simulated demonstrations, Diffraction grating patterns are restricted to those formed at normal incidence, The treatment of thin film interference is confined to parallel-sided films at normal incidence, The constructive interference and destructive interference formulae listed below and in the data booklet apply to specific cases of phase changes at interfaces and are not generally true
When a wavefront reaches a narrow aperture (comparable to the wavelength of the wave) then the wave diffracts. The pattern it produces on a screen is called a single-slit diffraction pattern. If we have two slits then we get an interference pattern. This experiment was first performed by Thomas Young in 1803 and is know as Young's Double Slits. The actual pattern observed with monochromatic light is the interference pattern, modulated by the diffraction pattern arising from the slit width of the individual slits.
Oxford Physics: pages 367 - 373
Hamper HL (2014): pages 193 - 197, in particular see exercises 36-37, p 194 and 38-39, p 197