Phase/polarisation

• Wavelength

  The distance between two consecutive peaks or troughs of a wave
• Phase difference

  Difference between the phase of two waves
• Radian

  The angle made by an arc equal to the radius of a circle
• Circumference of a circle

  2πr (r-radius)
• 2 pi arcs with length of the radius would fit in a circle
• There are 2 Radians in a full circle
• Waves in Pipes

  • The air that vibrates not the string
  • Standing waves - No energy transfer
  • The ends can be open or closed and this changes the pattern
• Closed end

  There will a node as the air particles cannot move
• Standing wave patterns in pipes

  1. 1st harmonic

  2. 3rd harmonic

  3. 5th harmonic
• Standing wave patterns in pipes

  • Node
  • Antinode
• Most light sources are unpolarised since electrons in atoms can move in any direction
• It is this movement that generates light
• Electrons can move in any direction
• Polarised light

  Oscillations restricted to ONE plane, usually horizontal or vertical
• Direction of polarisation

  Direction the ELECTRIC field oscillates in
• Ways of polarising light

  • Use a polariser
  • By reflection
• Polarising filters

  • Have long chain molecules aligned in the same direction
  • These molecules absorb the waves aligned in that direction
• If we have two polarising filters held at 90 all of the light is absorbed and none is transmitted
• Only transverse waves can be polarised
• Longitudinal waves oscillate parallel to the direction of travel so cannot be polarised
• Polarising by reflection

  1. Unpolarized incident light

  2. Polarized reflected light
• Reflection of light off of non-metallic surfaces results in some degree of polarization parallel to the surface
• Uses of polarisation

  • Polarising sunglasses
  • Aerial alignment
• Polarising sunglasses

  Reduce the glare of reflected light (e.g. off water or glass)
• Aerial alignment

  • Outdoor TV and radio aerials must be correctly aligned for the best reception
  • Transmitters generate plane-polarised waves which are picked up best by receivers with the same alignment