Wavefronts & Rays (SL IB Physics)

• Waves can travel in both two and three-dimensions:
  • A surface wave propagates in two dimensions and has circular wavefronts such as the surface of water
  • A spherical wave propagates in three dimensions and has spherical wavefronts such as sound or light

• Waves can be represented graphically in two different ways:
  • Wavefronts - lines joining all the points that oscillate in phase and are perpendicular to the direction of motion (and energy transfer)
  • Rays - lines showing the direction of motion (and energy transfer) of the wave perpendicular to the wavefront

Wavefronts and rays for transverse waves travelling in a horizontal plane

• Wavefronts are viewed from above and look like a series of parallel vertical lines
  • Peaks are often represented with a darker line
  • Troughs are represented with a fainter line
  • Some diagrams use only peak wavefronts

Waves can be represented using wavefronts

• The distance between successive peak wavefronts or (trough wavefronts) is equal to the wavelength of the waves

•  Wave phenomena such as reflection can be shown both as rays and as peak wavefronts
  • The ray is always perpendicular to the wavefronts

Reflection can be shown through rays or wavefronts

• Ripple tanks are commonly used to demonstrate the diffraction of water waves

 

A ripple tank can be used to demonstrate different wave effects

 

• When the frequency of a wave increases then the wavelength gets shorter
• It is possible to see this in a ripple tank: 
  • The distance between the wavefronts (wavelength) will reduce as the frequency of the motor increases

 

Ripple tank patterns for low and high frequency vibration