waves

• transverse wave = waves that oscillate perpendicular to the direction of energy transfer
• longitudinal wave = a wave that oscillates parallel to the direction of energy transfer
• Secondary waves (S-waves) are shear waves that are transverse in nature. Following an earthquake event, S-waves arrive at seismographstations after the faster-moving P-waves and displace the ground perpendicular to the direction of propagation.
• seismic waves = waves that travel through the earth and are caused by earthquakes
• examples of longitudinal waves = ultrasound, p waves and sound waves,
• example of transverse waves = ripples on surface water, vibration in guitar strings, S waves and electromagnetic waves
• compression = regions of high pressure due to particles being close together
• rarefactions = regions of low pressure due to particles being spread further apart
• demonstrated by :

  longitudinal - pushing and pulling a slinky

  transverse - moving a rope up and down rapidly
• • waves transfer energy and information, not matter
• wave amplitude = max displacement of point on wave from undisturbed position
• wave length = distance from point on wave to same position on adjacent wave. commonly peaks - peak or trough - trough
• frequency wave is no. waves which pass a given point each second
• frequency = hertz (Hz)
• wave speed 


  speed at which energy is transferred through medium
• wave velocity


  equal to product of wavelength and frequency of the wave
• wave speed = frequency x wave length
• period of wave


  length of time it takes for one full wave to pass through a point
• normal (reflection/refraction)


  vertical imaginary line which is perpendicular to the boundary
• when light reflects off a boundary it bounces off the smooth flat surface creating the angle of incidence (angle entering)which is the same as the angle of reflection (angle leaving)
• refraction


  change in speed of wave, it reached boundary between two media, usually resulting in change of direction
• when light refracted at boundary :

  • light changes speed in new medium
  • if new medium more dense, light travels slower and bend towards normal
  • if new medium less dense, light will travel faster and bend away from normal
• sound wave particles travel through solids by vibrating and transferring kinetic energy through the material
• how human ear works :

  1. outer ear collects sound which travels to ear
  2. sound wave causes eardrum to vibrate at same frequency
  3. this is amplifies by 3 ossicles by small bones in ear
  4. caused the hair in cochlea to vibrate
  5. cochlea converts the vibration into electrical signals which are passed to brain through auditory nerves
  6. brain converts electrical signals into sound
• human hearing frequency range = 20Hz - 20kHz
• ultrasound wave = 20, 000 Hz
• infrasound = 20Hz
• seismic waves produced by eathquakes, makes P waves (longitudinal) and S waves (transverse)
• • P waves travel through both solids and liquids
  • S waves only travel through solids
• P waves prove/ are evidence that the earth's core is liquid. The waves are detected on the other side indicating they're able to travel through the liquid within the earth's core
• detecting objects in deep water by using echo sound

  • high frequency sound waves are emitted, reflected and detected
  • time difference between emissions, detections and wave speed used to calculate distance of water depth
• sonar :

  • ultrasound waves emitted, reflect boundary and their echo is detected
  • speed of ultrasound known and also time it takes to detect the echoes
  • distance = speed x time
  • distance travelled is halved to give distance between emitter and boundary (wave has to travel there and back)
• foetal scanning :

  • ultrasound wave sent into body, passes through it and reflects off organs and tissues
  • device uses reflected ultrasound waves to product image of the foetus
  • ultrasound is safe and doesn't damage cells