waves and optics

• transverse wave

  direction of vibration is perpendicular to direction of energy propagation. e.g EM spectrum, S-waves
• longitudinal wave

  direction of vibration is parallel to direction of energy propagation. e.g sound waves, P-waves
• polarisation

  restricting the wave so that it can only oscillate in one plane, can only be done to transverse waves
• progressive wave

  wave that transfers energy from one point to another without transferring material
• standing wave

  waves made up of two progressive waves, don't transfer energy
• superposition

  when two waves meet and their displacements combine
• constructive interference

  superposition of in phase waves, amplitude increases
• destructive interference

  superposition of out of phase waves, amplitude cancels to 0
• node

  point on a standing wave of no displacement
• anti-node

  point on a standing wave of maximum displacement
• nth harmonic

  where the frequency is the nth multiple of the fundamental, has n anti-nodes
• fundamental frequency / first harmonic / f0

  the lowest frequency of vibration of a standing wave, one half wavelength fits on the string
• 2 uses of diffraction gratings:

  line absorption spectra (analysing chemicals or stars), X ray crystallography
• two types of dispersion:

  modal, material
• modal dispersion

  when light rays enter the fibre at different angles, causing them to take different paths and arrive at different times
• material dispersion

  different wavelengths diffract by different amounts, meaning different parts of the signal may arrive at different times
• what does dispersion cause and what is the problem?

  pulse broadening - causes signals to overlap, causing information loss
• critical angle

  the angle of incidence which produces an angle of refraction of 90
• how can modal dispersion be managed?

  use single mode fibre
• how can material dispersion be managed?

  use monochromatic light
• Describe interference pattern produced from double slit arrangement

  A central maximum with lower intensity maxima either side. Central maximum is twice the width of other maxima
• how does light wave change when passing into a higher optical density material?


  wavelength and speed change. Frequency constant
• How would interference pattern change with a longer wavelength?


  Central maximum would be wider. Other maxima are further apart
• How does interference pattern change when there are varying wavelengths?

  Central maximum is unchanged in width. Broader range of angles for each maximum
• When is double slit equation valid?

  When the distance between the slits and the screen is much larger than the slit separation