P2- Waves

• Waves transfer energy and information without transferring matter
• Particles of water or air 


  • Transverse
  • Vibrate and transfer energy but do not move with wave
  • Shown by placing a cork in water tank and generating ripples across surface
  • Cork will bob up and down on the oscillations of wave not travel across tank
• Frequency 


  • Number of waves passing a point per second
  • Measured in Hertz (Hz)
• Wavelength 


  • Distance from a point on one wave to a point in the same position on the next wave
  • Measured in metres
• Period


  Length of time it takes one wave to pass a given point
• Amplitude 


  Maximum distance/displacement from a point on the wave away from its rest position
• Velocity 


  Speed of the wave in the direction it is travelling
• Wave fronts


  Imaginary surface representing points of a wave that are at the same point in their cycle
• Transverse waves 


  Vibrations are at right angles to the direction of the wave
• Longitudinal waves 


  Vibrations are parallel to the direction of the wave
• Transverse waves

  • Water waves
  • Seismic s-waves
  • Electromagnetic waves
• Longitudinal waves examples

  • Sound waves
  • Seismic p-waves
• Wave speed (m/s) = frequency(Hz) x wavelength(m)
• Wave speed(m/s) = distance (m)/time (s)
• Measuring the speed of waves on water

  • Measure time it takes for a wave to travel between two fixed points
  • Speed can be calculated using s = d/t
• Calculate depth or distance from time and wave velocity
• Speed of sound waves

  Measuring time it takes for a sound to travel a certain distance

  Speed can be calculated using s=d/t
• Reflected 


  Wave bounces off
• Refracted


  Wave passes into the new material

  Changes the direction and speed it's travelling
• Transmitted


  Wave passes through the material and is not absorbed or reflected
• Absorbed


  Waves disappear as energy it's carrying is transferred to the material
• Refraction in different materials

  • Entering a high density material = Slower wave
  • Entering a low density material = Higher speed 
• Path of refracted ray


  • Wave crosses a boundary and slows down it will bend towards the normal
  • Wave crosses a boundary and speeds up it will bend away from the normal 
• Wave disturbances

  Action that causes something to sound/vibrate

  Vibrates

  • particles vibrate, hit air particles
  • air particle layer above to vibrate

  Air particles continue to vibrate until they reach bones in ear

  • vibrate to process sound

  Head on surface that vibrates

  • louder, doesn't have to travel through air
• Sound with frequencies greater than 20,000 Hz = ultrasound
• Sonar equipment

  • Carried on ships
  • Find depth of sea
  • Emit pulse of ultrasound, time how long it takes for sound to return
• Ultrasound 


  Used to make images inside the body

  • e.g. unborn babies
• Infrasound 


  • Nature produces infrasound in the form of seismic waves
  • Analysing how waves are absorbed and reflected by the inside of the planet
  • Scientists have been able to work out the internal structure of the earth.
• Mediums


  Less dense medium to a more denser medium

  • Wavelength of the sound wave increases
  • Frequency of the sound wave stays the same
  • Velocity of the sound wave also increases
• How the human ear detects sound

  Outer ear (pinna)

  • funnels sound into ear canal

  Sound waves travel along ear canal

  • cause eardrum to vibrate

  3 small bones transmit vibrations to cochlea

  • produces electrical signals which pass through auditory nerve to brain
  • Interpreted as sound
• Law of reflection

  Angle of incidence = angle of reflection
• Total internal reflection

  Angle of incidence is greater than the critical angle
• When the angle of incidence equals the critical angle the refracted light passes along the interface boundary of the glass block
• Diffuse reflection


  Rough surfaces reflect they scatter light in all direction
• When light is reflected on very smooth surfaces, the light is reflected evenly this is called specular diffusion
• Filters 


  Emit different colours of light by transmitting their colouring and absorbing all other colours
• An object looks a certain colour because it reflects light of that colour and absorbs all other colours
• A more powerful lens is more curved and bends light more
• Converging lens 


  Makes parallel rays of light converge at the focal point
• Diverging lens


  The focal point is the point which the rays seem to be coming after passing through the lens