General Waves

• What is a progressive wave?

  A wave that transfers energy along the wave
• What does the amplitude of a wave represent?

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

  Number of complete waves passing a point per second
• What characterizes a longitudinal wave?

  Oscillations are parallel to energy transfer direction
• What are the components of a longitudinal wave?

  Compressions and rarefactions
• What is a transverse wave?

  Oscillations are perpendicular to energy transfer direction
• What is meant by polarisation in waves?

  Oscillations restricted to a single plane
• How do polaroid filters work?

  Transmit oscillations parallel to their plane of polarisation
• What happens to the intensity of an unpolarised wave passing through a polaroid filter?

  50% of the wave intensity passes through
• How can the apparatus demonstrate that microwaves are vertically polarised?

  Signal is maximum when aerial is vertical
• What forms a stationary wave?

  Two waves travelling in opposite directions
• What are nodes in a stationary wave?

  Regions of zero displacement due to destructive interference
• What are antinodes in a stationary wave?

  Regions of maximum displacement due to constructive interference
• How do progressive waves differ from stationary waves?

  Progressive waves transfer energy; stationary waves do not
• Why can only specific frequencies be produced in a standing wave?

  Each fixed end must be a node
• What is the method to investigate the fundamental frequency of a stretched string?

  • Use a signal generator and weights
  • Measure string length and adjust tension
  • Produce standing wave with largest antinode
  • Plot graph of frequency against tension
• What happens to the harmonic observed when the mass per unit length of the string increases?

  Third harmonic is observed
• What defines coherent sources in wave interference?

  Same wavelength and constant phase relationship
• What is monochromatic light?

  Light of a single frequency or wavelength
• What conditions lead to constructive interference?

  Peaks meet peaks or troughs meet troughs
• What conditions lead to destructive interference?

  Peak meets trough or waves are in antiphase
• How are bright fringes formed in interference patterns?

  Superposition of waves from two slits
• Why does intensity reduce in a double-slit diffraction pattern?

  Waves travel different distances from each slit
• How does a single slit ensure coherence in the double-slit experiment?

  It acts as a single source of light
• What is the interference pattern with white light in a double slit?

  Central white fringe with colored fringes on sides
• What happens to the interference pattern when a violet laser is replaced with a green laser?

  Fringes become further apart and wider
• When is the Young’s double-slit equation valid for determining wavelength?

  When slit-screen distance is much greater than slit separation
• What are applications of a diffraction grating?

  • Determine wavelength of laser light
  • Analyze chemical composition of samples
  • Stabilize/filter laser light
  • Provide monochromatic sources
  • Used in optical encoders for motor control
• What is the interference pattern when a filter transmits only red and green light?

  Central fringe is a mix of red and green
• How does the spacing of fringes differ between red and green light?

  Red fringes are spaced further apart than green
• What effect does decreasing slit separation have on fringe separation?

  Fringe separation increases
• How does decreasing the distance between slits and screen affect the interference pattern?

  Uncertainty in measuring fringe separation decreases
• What happens to the uncertainty in wavelength determination with changes in slit separation and distance?

  • Percentage uncertainty in slit separation is largest
  • Uncertainties combine to affect wavelength measurement
• Where are green fringes located compared to red fringes?

  Green fringes are closer to the middle
• How does the spacing of red fringes compare to green fringes?

  Red fringes are 20% greater in spacing
• What is the relationship between the 6th green fringe and the 5th red fringe?

  The 6th green fringe overlaps with the 5th red fringe
• What apparatus does the student use to determine the wavelength of red light?

  Double slit apparatus and a screen
• What changes does the student suggest to improve the experiment?

  Decrease slit separation and distance to screen
• What is the effect of decreasing slit separation on fringe separation?

  Fringe separation increases
• How does decreasing slit separation affect uncertainty in wavelength measurement?

  Uncertainty in wavelength measurement decreases