Waves and Light: Diffraction

Waves and Light: Diffraction

Concepts of Wave Diffraction

  • Diffraction refers to the process by which waves spread out as they pass through an aperture or around the edges of a barrier.
  • The amount of diffraction (spreading) increases as the size of the gap or object causing the diffraction gets closer to the wavelength of the wave.
  • If the size of the gap or object is much larger than the wavelength of the wave, significant diffraction will not occur, and the wave will continue largely unaffected.
  • Monochromatic light (single wavelength) will produce a distinct diffraction pattern, with clear bright and dark fringes, due to the constructive and destructive interference of the diffracted waves.
  • Interference: This occurs when two or more waves combine to form a new wave pattern.
  • Constructive interference: This refers to when waves combine such that the resulting wave has a larger displacement.
  • Destructive interference: This is when waves combine to produce a displacement lesser than the original wave displacement.

Single-Slit and Double-Slit Diffraction

  • When light passes through a single slit, it diffracts and forms a central bright fringe surrounded by less intense fringes on a screen placed behind the slit. This is known as single-slit diffraction.
  • Double-slit diffraction, also known as Young’s double-slit experiment, demonstrates how light behaves as a wave.
  • Double-slit diffraction produces an observable light and dark interference pattern due to the path difference between the two slits resulting in constructive and destructive interference.

Wave-Particle Duality and Diffraction

  • Light behaves as both a wave and a particle, a concept known as wave-particle duality.
  • The diffraction and interference patterns observed in experiments provide evidence of light’s wave nature.
  • The particle nature of light is exemplified through the photoelectric effect, where light is seen to transfer energy in discrete packets, or quanta, known as photons.

Diffraction Gratings

  • A diffraction grating is an optical component with a periodic structure that splits and diffracts light into several beams travelling in different directions.
  • The directions of these beams depend on the spacing of the grating and the wavelength of the light.
  • Each order of light has a different angle to the central axis. The order of light is defined by its intensity and is denoted by the symbol ‘m’.