waves

• waves transfer energy in the direction they are travelling
• when waves travel through a medium the particles of a medium oscillate and transfer energy between each other, overall the particles stay in the same place and only energy is transferred
• what is the amplitude of a wave ?


  Maximum distance a wave varies from its rest position.
• what is wavelength ?


  distance between the same point of 2 adjacent waves
• what is frequency ?


  number of complete waves passing through a certain point per second

  measured in hertz (Hz)

  1 Hz is one wave per second
• transverse waves:

  • the oscillations (vibrations) are perpendicular (at 90 degrees) to the direction of energy transfer
  • most waves are transverse but some examples include:
  • all electromagnetic waves
  • ripples and waves in water
  • a wave on a string
• transverse waves have sideways vibrations
• longitudinal waves have parallel vibrations
• longitudinal waves:

  • the oscillations are parallel to the direction of energy transfer
  • examples are:
  • sound waves in air
  • shock waves
• when waves arrive at a boundary three things can happen :

  • absorption
  • transmission
  • reflection
• wave absorption :

  • waves are absorbed by the material the wave is trying to cross into- this transfers energy to the materials energy stores
• wave transmission:

  • the waves carry on travelling through the new material (often leads to refraction)
• ray diagrams :

  • used to show wave reflection
  • angle of incidence = angle of reflection
  • the angle of incidence is the angle between the incoming wave and the normal
  • the angle of reflection is the angle between the reflected wave and the normal
  • the normal is an imaginary line thats perpendicular to the surface at the point of incidence (where the wave hits the boundary)
• wave reflection can be specular or diffuse
• specular reflection occurs when a wave is reflected in a single direction by a smooth surface (e.g when light is reflected by a mirror you get a clear reflection)
• diffuse reflection is when a wave is reflected by a rough surface (e.g. a piece of paper) and the reflected rays are scattered in lots of different directions
• Microwaves are used by sattelites

  • communication to and from satellites uses microwaves
  • the microwaves used are able to easily pass through earths watery atmosphere
  • For satellite TV:
  • a signal from a transmitter is transmitted into space
  • where its picked up by a satellite receiver dish, this then transmits the signal back to earth in a different direction
  • where its received by a satellite dish on the ground
  • there is a slight time delay between the signal being sent and recieved due to the long distance the waves travel
• The EM wave spectrum :

  • Radio
  • Micro
  • Infra red
  • Visible
  • Ultra violet
  • X rays
  • gamma rays
• what is wave refraction?


  when a wave crosses a boundary between materials and changes direction
• EM waves are made up of oscillating electric and magnetic fields
• Whatare radio waves used for?

  radio, bluetooth, TV, mobiles
• Uses of microwaves 


  cooking, satellites, mobiles
• what are the dangers of microwaves?

  Burns
• what are the uses of infrared waves?

  fibre optic communication, photography
• what are the dangers of infrared radiation?

  cell damage, burns, damage to eyes
• what are the uses of visible light?

  photography, sight
• what are the use of UV waves ?

  sun beds, disinfecting water, sterilising medical equipment
• what are the dangers of UV radiation?

  sunburn, skin cancer, blindness
• Uses of X-rays 


  Medical imaging, cancer treatment
• dangers of X-rays 


  cell death, cancer, gene mutation
• uses of gamma rays

  cancer treatment, sterilising medical equipment, killing bacteria in food
• dangers of gamma rays

  Cell death (at high dosages), cancer, gene mutation
• convex lenses bulge outwards, it causes rays of light parallel to the axis to converge at the principle focus
• a concave lens caves inwards, its causes parallel rays of light to spread out (diverge)
• the principle focus of a convex lens is where rays hitting the lens parallel to the axis all meet
• the principle focus of a concave lens is the point where rays hitting the lens parallel to the axis appear to all come from
• the rules of refraction in a convex lens:

  1. an incident ray parallel to the axis refracts through the lens and passes through the principle focus on the other side
  2. an incident ray passing through the principle focus refracts the lens and travels parallel to the axis
  3. an incident ray passing through the centre of the lens carries on in the same direction
• the rule of refraction in a concave lens

  1. an incident ray parallel to the axis refracts through the lens and travels in line with the principle focus (so it appears to have come from the principle focus)
  2. an incident ray passing through the lens towards the principle focus refracts through the lens and travels parallel to the axis
  3. an incident ray passing through the centre of the lens carries on in the same direction
• what is a ’real image’?

  where the light from an object comes together to form an image on a ’screen’ like the image for end on the eyes retina
• what is a virtual image ?

  When the rays are diverging so the light from an object appears to be coming from a completely different place