Progressive and Stationary Waves

• phase difference and path difference interference

  A) even

  B) even

  C) odd

  D) odd

  E) path

  F) phase

  
• superposition happens when two or more waves pass through each other

  • when the waves cross, the displacements due to each wave combine
  • the principle of superposition says that when they cross, the resultant displacement = the vector sum of the individual displacements
• constructive interference

  • crest + crest = bigger crest
  • same with troughs
• destructive interference

  • crest + trough of equal size = the two displacements cancel out completely
  • if they arent the same size then destructive interference isnt total - for interference to be noticeable then the amplitudes should be nearly equal
• in phase = constructive interference
• antiphase = destructive interference
• points in phase

  • are at the same point in the wave cycle
  • have the same displacement and velocity
• points are in phase if they have a phase difference of 0 or 360 degrees
• points with a phase difference of odd number multiples of 180 degrees (pi radians or 1/2 wave cycles) are out of phase
• two sources are coherent if they have the

  • same wavelength
  • same frequency
  • a fixed phase difference between

  this must happen in order to get interference patterns