Waves

Waves

1. transverse waves

   • oscillations are perpendicular to direction of energy transfer
   • electromagnetic waves
     • eg: light

2. amplitude

   • maximum displacement of a point on the wave from its undisturbed position

3. wavelength

   • distance between the same point on two adjacent waves

4. longitudinal waves

   • oscillations are parallel to the direction of energy transfer
   • sound waves
     • ultrasound
       • when fired through a boundary, some will be partially reflected
       • distance = speed x time
       • used in indrustrial to see if there is cracks
   • shock waves

5. wave speed = frequency x wavelength

   • humans frequency = 20 to 20 000Hz
   • wavelength (m)

6. reflection

   • angle of incidence = angle of reflection
   • reflected at different boundaries
   • specular reflection
     • waves are reflected in a single direction
     • eg: mirror
     • happens on a completely smooth surface
   • diffuse reflection
     • rough surface
     • rays are scattered
     • normal is different for each ray
     • goes off in different directions
     • appears matte

7. lenses

   • convex
     • rays of light is brought together
   • concave
     • rays of light spread out
   • pricipal and lens axis
   • incident ray passing through the centre of the lens carries on in the same direction
   • virtual image
     • have to look through the lens
     • rays don't really cross
     • cannot be projected
   • magnification = image height / object height

8. small amplitude sounds quieter

   • less ripples
   • large amplitude is louder
     • more ripples

9. higher frequency sounds higher

   • taller waves
   • lower frequency sounds lower
     • smaller waves

10. visible light

    • primary colours
      • red
      • green
      • blue
    • objects absorb some wavelengths and reflect others
    • the wavelength reflected is the colour we see
    • colour filters only let some wavelengths pass
    • black absorbs all light
    • white reflects equally
    • refraction in light
      • slows down in denser materials
      • enters perpendicular, will carry on straight
      • enters more dense material, bend towards normal

11. black body radiation

    • all objects continually exchange radiation
    • object hotter than surroundings, emits more radiation
    • object colder, absorbs more
    • thermal equilibrium
      • same temp
    • best possible absorbers and emitters of radiation
    • surface that absorbs all radiant energy
      • also emits black body radiation
    • at cold temps, low intensity at all wavelengths
    • for hotter objects, the intensity for all wavelengths is higher
    • hot objects glow red (infra-red) and then very hot objects glow blue/white

12. sound

    • longitudinal
      • compressions and rarefractions
    • moves faster in more densly packet materials (solids)
    • can't travel in a vacum
    • when speed increases, wavelength increses
      • frequency doesn't change
    • can be absorbed, refracted and reflected
    • 20 to 20 000Hz
    • human hearing decreases due to wear and tear of the cochlea

13. seismic waves

    • s-waves
      • transverse
      • passes through solids
      • can't pass through liquids
    • p-waves
      • longitudinal
      • passes through liquids and solids
      • detected everywhere
    • caused by earthquakes, volcanoes and explosions
    • helped scientists to discover the internal structure of earth
    • both go through mantle
    • only p-waves go through inner core