Waves

• Stationary waves


  Waves that do not travel through a medium but remain at the same place on the medium
• Stationary waves

  • The disturbance produced stores energy in the medium
  • There is no net transfer of energy through the medium
• Nodes

  Points where stationary waves don't vibrate
• Anti-nodes

  Points where stationary waves vibrate with maximum amplitude
• The distance between two consecutive nodes is half the wavelength
• The distance between two consecutive anti-nodes is half the wavelength
• The distance between an anti-node and the next node is a quarter of the wavelength
• Doppler effect

  The apparent change in frequency of waves due to the motion of the source or the observer
• If the source moves towards the observer, the observed frequency is greater than the actual frequency
• If the source moves away from the observer, the observed frequency is less than the actual frequency
• Applications of Doppler effect

  • Speed traps to determine speed of oncoming cars
  • Determining speed of stars and galaxies (red shift)
• Polarisation

  Confining the vibrations of transverse waves to one plane only
• Unpolarised light

  • Light vibrations occur in all directions perpendicular to the direction of travel
• Polaroid filters

  Reduce intensity of light by confining vibrations to one plane
• Polarisation by reflection

  Light reflecting off a plane surface becomes polarised vertically or horizontally
• Applications of polarisation

  • Polaroid sunglasses reduce glare
  • Polarised TV signals prevent interference
• Constructive interference

  • Waves combine to give a wave of larger amplitude
• Destructive interference

  • Waves combine to give a wave of smaller amplitude
• Coherent sources

  • Sources with the same frequency and in phase
• If coherent waves have a path difference of half a wavelength, they will be out of phase and result in complete destructive interference
• If coherent waves have a path difference of a whole number of wavelengths, they will be in phase and result in constructive interference
• Interference pattern

  A pattern of alternate regions of constructive and destructive interference
• Transverse wave

  • Vibration is perpendicular to the direction of motion
• Longitudinal wave

  • Vibration is parallel to the direction of motion
• Wavelength

  The distance between two identical points on a wave
• Amplitude

  The maximum displacement of a point from its mean position
• Frequency

  The number of complete waves passing per second, or the number of complete oscillations per second
• Period

  The time for one complete oscillation
• A seimic wave is a mechanical wave of acoustic energy that travels through earth
• Interference

  Is when two periodic travelling waves meet and come to form a new wave
• Stationary waves definition

  Whe 2 period waves with the same frequency and amplitude travelling in opposite directions meet and interfere
• Electromagnetic waves


  Traveling waves whose speed is 3 x 10 m s¹ in a vacuum (the speed of light), less in other media
• Electromagnetic waves


  • Show the properties of waves including Interference and diffraction
• Frequency and wavelength of electromagnetic waves

  Related by the equation c=fλ
• Electromagnetic spectrum


  • All possible frequencies of electromagnetic radiation
• You must know relative positions of radiations in terms of wavelength and frequency
• Radio waves


  Used in telecommunications
• Microwaves


  Used in cooking, medical treatment and telecommunications
• Infrared waves


  Frequencies just below those of red light, emitted by hot objects, used in medical imaging and night vision
• Detecting infrared radiation


  1. Place a blackened thermometer bulb in the IR radiation

  2. Temperature will rise indicating presence of IR