diffraction

• • When waves pass through a narrow gap, they spread out. This spreading out is called diffraction.
  • Diffraction is defined as the spreading of a wave into regions where it would not be seen if it moved only in straight lines after passing through a narrow slit or past an edge
  • When light travels through an aperture or passes the edge of an obstacle, it deviates from the straight-line direction and appears to spread out.
• Gratings

  • a flat object which has lots of equally spaced lines. These lines allow waves to go through and diffract.
  • When they diffract, the waves overlap and superpose
  • we see an interference pattern of regularly spaced bright spots and dark lines called fringes.
  • diffracted waves start to interfere with one another via constructive AND destructive interference.
• Gratings pt2

  • only form if the diffracted light waves are coherent
  • Coherent literally means ‘sticking together’ and is used to describe waves whose superposition gives a visible interference pattern.
  • Coherent waves have the same frequency and wavelength, with a constant phase difference.