Of sound

• The refraction of a sound wave is measured by comparing θi to θr and by describing the wave's direction change as towards or away from the normal compared to θi
• Normal: a perpendicular line on a medium's boundary
• As the sound wave travels from air to rock:

  • the rock is solid ∴v2 is greater than v1 in air
  • f1 = f2, hence time between fronts remain constant (T)
  • as v2>v1 spacing of wavelengths increase (λ2>λ1) thus causing angle of refraction to increase and bend away from the normal (θr>θi)

  
• As sound wave travels from steel to air:

  • v2 in air is less than v1 in steel (v2<v1) ∴ spacing between fronts decreases (λ2<λ1)
  • hence angle of refraction decreases, bending towards the normal (θr<θi)

  
• Snell's Law: $\sin(r) /sin(i) =$$v2/v1 =$$λ2/λ1$
• Summary:

  • when a wave speeds up, wavelength increases, bending the front away
  • when a wave slows, wavelength shortens, bending the front towards
  • frequency is unaffected
  • wave fronts reaching perpendicular are not affected and continue in the same direction
  • when refraction occurs a proportion of the wave is still reflected
• Critical angle (θc): a particular angle of incidence where the refracted angle equals 90deg, lying along the medium's interface

  -> known as TOTAL INTERNAL REFLECTION