wave behaviour

• If wave A hits peaks and troughs at the same time as B, then A and B are in phase (phase difference zero). add up to give a big resultant wave -> constructive interference

  
  

  If A hits peak when B hits trough. This means the waves are perfectly opposite and we say they are perfectly out of phase. a flat line as resultant wave -> Zero wave -> destructive interference

  
• wave lag

  
• Resultant waves are the total waves you get from adding up waves that interfere

  
• Anti-node -> constructive interference. At anti-nodes, crests meet crests and troughs meet troughs -> causes a point of maximum disturbance, with extra big crests and extra big troughs.

  Node -> destructive interference. At nodes, crests and troughs cancel out and nothing is left.
• Beats -> adding two waves with different (but similar) frequencies. E.g 59Hz and 60Hz, start at same point but higher frequency wave moves faster than lower frequency -> gap made between waves -> phase difference appears and changes over time.

  
• When waves of slightly different frequencies add up, their phase difference cycles through being 0 and 360 degrees back to 0 and so on. So their interference cycles between constructive and destructive. The resultant wave is a called a beating wave
• frequency of resultant wave for beats - fb -> difference between the two waves' frequencies -> fb = [f1 - f2]
• beats can be used to tune instruments