Waves

• Displacement: The distance and direction of a particle from the equilibrium position
• Amplitude


  Maximum displacement from equilibrium
• Wavelength


  Shortest distance between two particles in phase
• Frequency


  Number of wave cycles occuring each second
• Wave Speed


  Distance travelled by a wave each second
• Phase difference: Measured in degrees or radians, the amount by which one wave lags behind another wave
• Path difference: Measured in metres, the difference in the lengths of two waves
• Progressive Wave


  Waves whose oscillations transfer energy
• Transverse wave


  Oscillations are perpendicular to direction of propagation
• Longitudinal wave


  Oscillations are parallel to direction of propagation
• Which waves can be polarised?

  Transverse waves
• Polarisation: The restriction of a wave so that it can only oscillate in a single plane.
• Superposition


  The point where waves meet
• Total displacement: Equal to the sum of the individual displacement at that point
• Constructive interference: Where the waves are in phase with each other
• Destructive interference


  Where the waves are in antiphase
• Stationary wave


  A wave that stores energy
• How is a stationary wave formed? a wave is reflected and travels back in the opposite direction, the waves undergo superposition forming nodes and antinodes
• Antinodes


  Points of maximum amplitude on a stationary wave
• Nodes


  Points of zero amplitude on a stationary wave
• Fundamental frequency


  First harmonic
• Coherent sources: waves have the same frequency with a constant phase difference
• Young's double slit experiment: Two slits act as coherent sources, the light diffracts at the slits and the two waves superpose, forming an interference pattern
• Double slit formula


  W =λD/s
• Evidence for the wave nature of EM radiation: Diffraction and interference are wave properties
• Diffraction: The spreading out of waves when they pass through a gap or over an edge
• Intensity: A measure of the power delivered per unit area
• Increasing slit width


  Increases intensity but narrow central maximum
• Decreasing slit width


  Decreases intensity but wider central maximum
• Refraction: The changing of speed when it crosses into a new medium
• More optically dense medium: The wave will slow down and bend towards the normal
• Less optically dense medium: The wave will speed up and bend away from the normal
• Absolute refractive index: The ratio between the speed of light in a vacuum and the speed of light in a material.
• Relative refractive index: The ratio of the speed of light in one material to the speed of light in another
• Snell's law


  n1sinθ1 = n2sinθ2
• Critical angle: the minimum angle of incidence for which a light ray is totally reflected within a medium
• Conditions of total internal reflection: The light must travel from a more optically dense to a less optically dense material.

  The angle of incidence must exceed the critical angle.
• Critical angle formula


  sinθc = n2/n1
• Step-index optical fibres: Core made of a high-refractive index material

  Cladding made of a low-refractive index material
• Purpose of cladding in step-index optical fibres: Prevents the core from being damaged

  Prevents information from being transferred between cores

  Provides tensile strength to optical fibre