Diffraction Examples to Know for College Physics II

Diffraction is a fascinating phenomenon where waves, like light and sound, bend and spread when passing through openings or around obstacles. Understanding diffraction helps explain various patterns and behaviors in mechanics, sound, oscillations, and waves, enhancing our grasp of wave interactions.

1. Single slit diffraction

   • Occurs when light passes through a narrow slit, causing the light to spread out.
   • The intensity pattern on a screen shows a central maximum and several smaller maxima on either side.
   • The width of the slit affects the width of the central maximum; narrower slits produce wider patterns.

2. Double slit diffraction

   • Involves two closely spaced slits, leading to an interference pattern of bright and dark fringes.
   • The pattern results from the superposition of waves emanating from both slits.
   • The spacing between the slits and the wavelength of light determine the fringe spacing.

3. Diffraction gratings

   • Composed of many closely spaced slits or grooves, producing sharp and well-defined interference patterns.
   • Used to separate light into its component wavelengths, allowing for spectral analysis.
   • The angle of diffraction depends on the wavelength and the spacing of the grating lines.

4. Circular aperture diffraction (Airy disk)

   • Light passing through a circular aperture creates a diffraction pattern known as an Airy disk.
   • The pattern consists of a central bright spot surrounded by concentric rings of decreasing intensity.
   • The size of the Airy disk is influenced by the aperture diameter and the wavelength of light.

5. X-ray diffraction in crystals

   • Utilizes the wave nature of X-rays to study the atomic structure of crystals.
   • The diffraction pattern provides information about the arrangement of atoms within the crystal lattice.
   • Bragg's law relates the angles of diffraction to the spacing between crystal planes.

6. Diffraction of water waves

   • Water waves bend around obstacles and spread out after passing through openings, similar to light.
   • The extent of diffraction depends on the wavelength of the waves relative to the size of the obstacle or opening.
   • Observed in phenomena such as wave patterns in harbors or around piers.

7. Sound wave diffraction around obstacles

   • Sound waves can bend around obstacles and spread out in the region behind them.
   • This property allows sound to be heard even when the source is not in direct line of sight.
   • The degree of diffraction is influenced by the wavelength of the sound relative to the size of the obstacle.

8. Diffraction of light by a hair or thin wire

   • Light passing near a thin object, like a hair, creates a diffraction pattern that can be observed.
   • The pattern consists of alternating bright and dark fringes due to the interference of light waves.
   • This phenomenon demonstrates the wave nature of light and can be used in optical experiments.

9. Fresnel and Fraunhofer diffraction

   • Fresnel diffraction occurs when the source or observation point is at a finite distance from the aperture, leading to complex patterns.
   • Fraunhofer diffraction assumes that both the source and observation point are at infinity, simplifying calculations.
   • Both types are essential for understanding how light behaves when encountering obstacles or apertures.

10. Diffraction in optical instruments (telescopes, microscopes)

    • Diffraction limits the resolution of optical instruments, affecting image clarity.
    • Telescopes and microscopes must account for diffraction effects to enhance image quality.
    • Techniques such as using larger apertures or advanced optics help mitigate diffraction limitations.