Waves

• Waves transfer energy without transferring matter
• Waves cause particles to

  oscillate or vibrate
• amplitude


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


  distance from one crest / trough to another
• frequency


  number of complete waves passing a point per second
• time period


  time it takes for a full cycle of the wave
• two types of wave

  longitudinal and transverse
• transverse waves

  oscillations are perpendicular to the direction of energy transfer
• two examples of transverse waves

  1. light waves
  2. s-waves
• longitudinal waves

  oscillations are parallel to the direction of energy transfer
• 2 examples of longitudinal waves

  1. sound waves
  2. p-waves
• wave speed equation

  wave speed = frequency x wavelength
• speed of sound

  330 m/s
• three things that can happen to waves

  absorbed, reflected or transmitted
• law of reflection

  angle of incidence = angle of reflection
• specular reflection


  reflection on a smooth surface, a produces a clear image
• diffuse reflection


  reflection on a rough or matte surface, produces an unclear reflection or no reflection
• what type of waves are em waves?

  transverse waves
• all em waves transfer energy from a source to an absorber
• order of em waves (red monkeys in vans use x ray guns)

  radio, micro, infrared, visible light, uv, x ray, gamma rays
• refraction

  when a wave enters a more dense medium its speed slows down and the direction changes towards the normal
• what is the relationship between wave speed and wavelength?

  inversely proportional
• what happens to the frequency after a change in wave speed or wavelength

  it stays the same
• optical density

  how quickly light can travel through a material - the higher the optical density, the slower light waves travel through it
• why is a thin beam of light used in the refraction practical

  so you can easily see the middle of the ray when tracing and measuring angles from it
• uses of radio waves

  bluetooth, TV, communications
• em waves are made up of

  oscillating electric and magnetic fields
• uses of microwaves

  cooking, communications, radar
• how do microwave ovens work

  microwaves are absorbed by water molecules in the food, which transfer the energy to the rest of the food, heating it
• uses of infrared waves

  thermal imaging, heating
• what are optical fibres

  thin glass fibres that carry data by reflecting light rays internally until they reach the end of the fibres
• uses of optic fibres

  telecommunication, medical imaging (endoscopy, colonoscopy)
• uses of visible light

  optic fibres telecommunications, imaging
• uses of UV rays

  tanning, attracting insects, security marking
• uses of x rays

  medical imaging, security (imaging inside objects)
• uses of gamma rays

  sterilising medical equipment, killing cancer cells
• fluorescence

  where UV radiation is absorbed and then visible light is emitted causing fluorescent colours to look bright
• why do people naturally get a sun tan

  the sun emits UV radiation, and prolonged exposure causes a tan
• how do x rays show bones

  x rays struggle to pass through denser materials like bone and metal, so the amount of radiation absorbed gives an image
• advantages of optic fibres

  information sent along can be multiplexed so more information can pass through