Waves

• Transverse wave


  A wave where vibrations occur perpendicular to the direction the wave is travelling
• Longitudinal wave


  A wave where vibrations occur parallel to the direction the wave is travelling
• Amplitude


  The maximum distance between the peak or trough of a wave and its equilibrium point
• Wavefront


  A horizontal line drawn linking all the peaks in a set of waves
• Wavelength


  The distance from point on a wave to the same point on the next wave
• Frequency


  Number of waves per second
• Period of a wave


  Time taken to complete one wave cycle
• Properties common to all waves


  • They can be reflected
  • They can be refracted
• Doppler effect


  The change in frequency and wavelength caused by relative movement of the source of wave or observer
• Doppler effect in sound waves

  • When an ambulance goes past you the siren decreases in pitch
  • This is because the wavelength of the sound waves increases
• Doppler effect in light waves


  • Light from distant planets looks red (it's red-shifted)
  • Because planets are moving away from us so wavelength becomes longer and therefore moves to the red spectrum
• EM waves used in cooking


  • Microwaves
  • Infrared radiation
• Infra-red radiation


  Causes burns
• UV


  Causes skin cancer
• X- rays and gamma rays danger

  • Ionising radiation
  • Mutation leading to cancer
• Properties common to all EM waves


  • All transfer energy
  • All travel at the same speed in a vacuum
  • Can be reflected
  • Can be refracted
  • Can be diffracted
  • All transverse waves
• Optic fibres advantages


  • Carry more information per second
  • More secure
• x-rays and gamma rays similar

  • Both short wavelength EM waves
  • Carry lots of energy per second
• X-rays and gamma rays differ


  • X-rays are made when electrons moving at high speeds are stopped
  • Gamma rays are released from unstable nuclei
  • Gamma is more penetrative
  • Gamma has shorter wave length
• Light waves


  • Transverse wave
  • Transfer energy
  • Can be reflected
  • Can be refracted
  • Can be diffracted
  • A wave where vibrations occur perpendicular to the direction the wave is travelling
• Normal line


  A line drawn perpendicular to the mirror
• Law of reflection


  Angle of incidence = angle of reflection
• Refraction


  A change in direction of waves when they travel across a boundary from one medium to another
• Light ray entering and leaving a glass block


  1. Bends towards the normal as it enters the block

  2. Bends away from the normal as it leaves the block
• Critical angle


  Angle of incidence beyond which rays of light are totally internally reflected
• Total internal reflection

  • When the angle of incidence is greater than the critical angle
  • All light is reflected, none is refracted
• How optical fibres work


  1. Total internal reflection

  2. Core of fibre made out of glass with high refractive index

  3. Cladding is made out of glass with lower refractive index

  4. Light entering core is at an angle greater than the critical angle so light is TIR
• Uses of optical fibres

  • Endoscope - used in keyhole surgery
  • Communication as less energy is lost when compared to using copper wiring
• Sound waves


  • Longitudinal waves
  • Transfer energy
  • Can be reflected
  • Can be refracted
  • Can be diffracted
• Pitch and frequency


  The higher the pitch, the higher the frequency of a sound wave
• Loudness and amplitude


  The louder the sound, the higher the amplitude
• Oscilloscope


  A machine used to view sound waves
• Radiowaves uses


  Used for broadcasting and communications
• Microwave uses


  Used for cooking and satellite communication
• Microwaves dangers


  Danger is internal heating of body tissues
• Infrared uses


  Used for heaters, cooking remote controls, and night vision
• Infrared danger


  Danger is skin burns
• Visible light uses


  Used for optical fibres and photography
• Ultraviolet uses


  Used for detecting forged banknotes and fluorescent lamps in sun beds
• Ultraviolet dangers


  Dangers are damage to surface cells which can lead to skin cancer and blindness