SP4

• Transverse waves


  Oscillate at right angles to the direction that they travel in
• Longitudinal waves


  have oscillations along the same line as they travel in
• Key fact about waves

  The direction they travel in is the same one they transfer energy and matter
• Examples of transverse waves


  -Light waves

  -Electromagnetic waves
• Examples of longitudinal waves 


  -Sound waves

  -Seismic P-waves
• Amplitude


  The displacement from the rest position to a crest/trough
• Wavelength


  The length of a full cycle of the wave
• Frequency


  number of complete cycles of the wave passing a certain point per second
• Period of a wave


  number of seconds its takes for a full cycle to pass a point
• Wave speed


  Frequency x wavelength

  
• When a wave meets a boundary three things can happen:

  1. Wave is absorbed
  2. Wave is transmitted
  3. Wave is reflected
• Refraction


  When a wave hits a boundary at an angle and the change of speed causes a change in direction
• Law of reflection


  angle of incidence = angle of reflection
• Investigating refraction

  1. Glass block on a piece of paper and trace it
  2. Use ray box to shine a ray on the block
  3. Trace incident line and emergent ray
  4. Remove block and join up rays to show path of reflected ray
  5. Draw normal
  6. Measure angle between incident ray and normal and angle between refracted and normal
• Total internal refraction


  Wave is reflected back into the material
• When does TIR happen?

  -Waves travels through dense materials
• Specular reflection


  Parallel waves are reflected in a single direction by a smooth surface

  e.g. light in a mirror
• Diffuse reflection


  parallel waves are reflected by a rough surface and the rays are scattered

  e.g. a piece of paper
• What are sound waves caused by?


  Vibrating objects
• Sound waves


  -Faster in liquids compared to gases

  -Faster in solids than liquids
• How does sound travel through the ear?

  1. Pinna which collects the sound
  2. Through ear canal
  3. Ear drum passes vibration to the ossicles
  4. The ossicles amplify the vibrations
  5. Cochlea
  6. Tiny hairs in cochlea detect vibrations and create electrical signals called impulses
  7. Impulses travel along neurons in the auditory nerve to the brain
• Infrasound waves


  Too low in frequency to hear

  ~Under 20 Hz
• Ultrasound waves


  Frequencies too high to hear

  ~Over 20,000 Hz
• Uses of ultrasound


  -Medical imaging

  -Echo sounding
• Echo-sounding


  Type of sonar used by boats to find out distance to seabed or locate objects
• What do earthquakes and explosions cause?


  Seismic waves
• P-waves


  -Longitudinal

  -Travel through liquids and solids

  -Faster than S-waves
• S-waves


  -Transverse

  -Only travel through solids