light and sound

light and sound

1. comparing light and sound waves

   • both travel as waves - but are not identical
     • light is transverse
       • can travel through a vacuum
       • can be reflected, refracted and diffracted
       • can be interfered
     • sound is longitudinal
       • cannot travel through a vacuum as sound can only pass through a solid, liquid or gas
       • can be reflected, refracted and diffracted
       • can be interfered
   • diffraction is the spreading out of waves when they pass through a gap. the extent to which this happens depends on the wavelength and size of the gap

2. law of reflection

   • both waves reflect from surfaces
     • angle of incidence = angle of reflection
     • both angles are measured from the normal
       • normal is an imaginary line at right angles to the plane mirror.
     • smooth surfaces produce strong echoes then sound waves hit then, and they can act as mirrors when light waves hit them.
     • rough surfaces scatter sound and light in all directions.

3. refraction

   • both waves change speed when they pass across the boundary between two substances with different densities (air and glass)
     • this causes them to change direction (refraction)
   • speed of light is determined by the material through which it travels
     • refractive index = sin i / sin r
       • i is angle of incidence
       • r is the angle of refraction