Progressive and Stationary

• What is a progressive wave?

  A wave that transfers energy along the wave from one point to another
• What characterizes coherent sources?

  Constant phase difference between sources
• What is a longitudinal wave?

  Direction of oscillations is parallel to energy transfer
• What is a transverse wave?

  Direction of oscillations is perpendicular to energy transfer
• How is amplitude defined?

  Maximum displacement from the equilibrium position
• How is frequency defined?

  Number of complete waves passing a point per second
• How do progressive waves differ from stationary waves?

  • Progressive waves transfer energy along the wave.
  • Stationary waves do not transfer energy.
  • Progressive waves have the same amplitude at all points.
  • Stationary waves have varying amplitudes.
  • Progressive waves have points out of phase within one wavelength.
  • Stationary waves have points in phase between nodes.
  • Progressive waves have no regions of minimum amplitude.
  • Stationary waves have regions of high displacement (antinodes) and zero displacement (nodes).
• How is a stationary wave formed?

  By two waves travelling in opposite directions
• What are the features of a stationary wave?

  Nodes and antinodes are present
• Why can only waves of specific frequencies be produced in a standing wave?

  Because standing wave shapes must be in half wavelength intervals
• What is the role of coherence in stationary waves?

  • Waves must have the same frequency or wavelength
  • They undergo superposition as they pass through each other
• What are nodes in a stationary wave?

  Regions of zero displacement due to destructive interference
• What causes nodes to form in a stationary wave?

  Positive wave peak cancels with negative wave peak
• What are antinodes in a stationary wave?

  Regions of maximum displacement due to constructive interference
• How do particles behave around a node in a stationary wave?

  Particles either side of a node are in antiphase
• How do particles behave between nodes in a stationary wave?

  Particles between nodes are in phase
• How does amplitude vary in a stationary wave?

  Amplitude varies between nodes
• What must each fixed end of a stationary wave be?

  Each fixed end must be a node
• How is the number of half wavelengths related to nodes in a stationary wave?

  The number of half wavelengths is nodes minus one
• What is meant by polarisation?

  Restriction of wave oscillations to one plane
• How do polaroid filters work?

  They transmit oscillations parallel to their polarization
• What type of waves can be polarised?

  Transverse waves
• What happens to oscillations perpendicular to the plane of polarisation?

  They are fully absorbed by the filter
• What is the effect of polarisation on the intensity of an incident wave?

  It reduces the intensity of the incident wave
• What percentage of an unpolarised wave passes through a polaroid filter?

  50%
• What characterizes unpolarised waves?

  Oscillations exist in more than one plane
• What is the relationship between the plane of polarisation and the transmitted oscillations?

  Only oscillations parallel to the plane are transmitted
• (Stationary)Particles separated by an odd number of nodes


  Are $\pi$ / 180 out of phase
• (Stationary)Particles separated by an even number of nodes

  Are in phase/ 0 phase difference
• Phase difference equation for progressive

  Radians = $2\pi\frac{d}{\lambda}$

  Degrees = $360\frac{d}{\lambda}$