Waves

• Wave

  Oscillation of particles or fields
• Wave


  • Cycle - one complete vibration
  • Amplitude - magnitude of displacement
  • Wavelength - distance of one wave cycle
  • Wave speed - speed of wave propagation
• Wave

  1. Cycle

  2. Wavelength

  3. Period - time taken for one cycle

  4. Frequency - number of cycles per second

  5. Phase - position along wave cycle

  6. Phase difference - amount one wave lags behind another
• Waves can be reflected and refracted
• Reflection


  Wave is bounced back when it hits a boundary
• Refraction


  Wave changes direction as it enters a different medium
• Frequency is the inverse of

  period
• Wave equation


  Wave speed = wavelength x frequency
• Transverse waves


  • Vibrate at right angles to direction of energy transfer
  • Can be polarised
• Longitudinal waves


  • Vibrate along direction of energy transfer
  • Consist of compressions and rarefactions
• Polarisation is evidence that electromagnetic waves are transverse
• Polarising filter


  1. Transmits vibrations in only one direction

  2. Blocks vibrations in other directions
• TV and radio signals are polarised
• To receive a strong signal, receiving aerial must be aligned with transmitting aerial
• Superposition


  When two or more waves pass through each other
• Superposition


  1. Displacements due to each wave combine

  2. pass through each other
• Principle of superposition


  The vector sum of the individual displacements
• Interference

  Can be constructive or destructive
• Constructive interference


  • A crest plus a crest gives a bigger crest
  • A trough plus a trough gives a bigger trough
• Destructive interference


  • A crest plus a trough of equal size gives nothing
  • The two displacements cancel each other out completely
• For the interference to be noticeable, the two amplitudes should be nearly equal</b>
• In phase


  Two points on a wave are at the same point in the wave cycle<|>Have the same displacement and velocity
• Converting between degrees and radians

  1. To convert from degrees to radians, multiply by π/180

  2. To convert from radians to degrees, multiply by 180/π
• Points in phase

  • Have a phase difference of zero or a multiple of 360
  • Have a phase difference of odd-number multiples of 180
• Two different waves being in phase happens because both waves came from the same oscillator
• Interference


  The superposition of two or more waves resulting in a new wave pattern
• Coherence

  • Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them
• interference patterns

  The two sources must be coherent
• In order to get clear interference, the waves of various amplitudes and frequency must be combined
• Constructive interference


  Occurs when the path difference is a whole number of wavelengths
• Destructive interference


  Occurs when the path difference is an odd multiple of half a wavelength
• Investigating how interference varies with position

  Use a microphone and an oscilloscope
• At any point an equal distance from two coherent and in-phase sources, you will get constructive interference
• Constructive interference occurs when the path difference is a whole number of wavelengths
• Destructive interference occurs when the path difference is an odd multiple of half a wavelength
• Stationary Waves


  Progressive Waves Reflected at a Boundary Can Create a Stationary Wa
• Third Harmonic


  The third harmonic is three times the frequency of the first hamonic.
• You can Demonstrate Stationary Waves with Microwaves and Sounds
• wave that has a node at each end and a single antinode. This is the frequency of the Second harmonic.
• You should find the following from your investigation:

  • The longer the string, the lower the resonant frequency
  • The heavier (.e. the more mass per unit length) the string, the lower the resonant frequency
  • The looser the string the lower the resonant frequency