Path Difference and Coherence

• What is the principle of superposition?

  The displacement is the sum of individual waves

  
• What happens when two or more waves overlap?

  Their amplitudes combine through superposition

  
• What are areas of zero displacement in water waves called?

  Nodes
• What does the superposition of surface water waves demonstrate?

  It shows areas of zero and increased displacement

  
• How can superposition be analyzed clearly?

  Using a vertical displacement-amplitude graph

  
• What is the effect of interference?

  It results from the superposition of waves

  
• What occurs when two waves are in antiphase?

  They cancel each other out
• What is destructive interference?

  When waves cancel each other out

  
• What is constructive interference?

  When waves combine to increase amplitude

  
• What happens at points where waves are neither in phase nor antiphase?

  The resultant amplitude is intermediate
• What must waves be to undergo constructive and destructive interference?

  They must be coherent

  
• What defines coherence in waves?

  Same frequency and constant phase difference
• What is path difference?

  The difference in distance traveled by two waves
• How does path difference relate to phase difference?

  Path difference compares distances, phase compares phases
• What determines whether there is constructive or destructive interference?

  The path difference between two coherent waves

  
• What is the condition for constructive interference?

  Path difference = $n\lambda$
• What is the condition for destructive interference?

  Path difference = $\left(n + \frac{1}{2}\right)\lambda$
• How is path difference generally expressed?

  In multiples of wavelength
• What does a wavefront diagram represent?

  Wave behavior and interference between waves
• What occurs at the blue dot in a wavefront diagram?

  Constructive interference occurs
• What occurs at the green dot in a wavefront diagram?

  Destructive interference occurs
• How can the number of wavelengths be counted in a wavefront diagram?

  To determine interference type at a point
• What is the path difference at point P if the waves from S have a path difference of $6\lambda$ and $4\lambda$?


  Path difference = $2\lambda$
• What happens when two waves are in phase?

  They cause constructive interference

  
• What happens when two waves are in antiphase?

  They cause destructive interference

  
• What are the key differences between constructive and destructive interference?

  • Constructive interference:
  • Waves in phase
  • Resultant amplitude increases
  • Destructive interference:
  • Waves in antiphase
  • Resultant amplitude cancels out

  
• What are the conditions for constructive and destructive interference?

  • Constructive interference:
  • Path difference = $n\lambda$
  • Destructive interference:
  • Path difference = $\left(n + \frac{1}{2}\right)\lambda$