Interference

• Define coherence

  Coherent waves have a fixed phase difference and the same frequency and wavelength
• why is a laser useful in showing interference and diffraction

  it produces monochromatic (same wavelength/colour) light so diffraction and interference patterns are more defined
• What was Young’s double-slit experiment

  A single light source is directed towards two slits which each act as a coherent light source, the light interferes constructively and destructively to create an interference pattern
• define the interference pattern created using white light

  A bright white central maximum flanked by alternating spectral fringes of decreasing intensity with violet closest to the zero order and red furthest
• why does an interference pattern form when light is passes through a single slit

  The light diffracts as it passes through the slit, where the waves are in phase, contructive interference occurs making bright fringes and where the waves are completely out of phase, destructive interference occurs making a dark fringe
• increasing the slit width increase the width of the central diffraction maximum. True or False

  False, the slit is not so close to the wavelength in size so less diffraction occurs - the central maximum becomes narrower and more intense
• Is the following a double slit pattern, single slit pattern or a diffraction grating pattern

  Single Slit

  
• What is the approximates refractive index of air

  1
• when light enters a more optically dense medium does it ben towards or away from the normal

  Towards the normal
• when does total internal reflection occur

  when light is at a boundary to a less optically dense medium and the angle of incidence is greater than the critical angle
• what is the purpose of the cladding in a step index optical fibre

  • Protects core from scratches which would allow light to escape and degrade the signal
  • Allows TIR as it has a lower refractive index than the core
• How does signal degradation by absorption in an optical fibre affect the received signal

  Part of the signal’s energy is absorbed by the fibre so its amplitude is reduced