P6 - Waves

• Transverse wave have oscillations (vibrations) perpendicular to direction of energy transfer
• Longitudinal waves have oscillations (vibrations) parallel to the direction of energy transfer
• Examples of transverse waves:

  • all electromagnetic waves

  • ripples and waves in water

  • wave on string
• Frequency is the number of complete wavelengths passing a point every second.
• Examples of longitudinal waves:

  • sound waves - ultrasound

  • shock waves
• angle of incidence = angle of reflection
• What is the angle of incidence?

  angle between incoming wave and normal
• What is the angle of reflection?


  angle between reflected wave and normal
• What is the normal line?

  imaginary line perpendicular to surface, shown as dotted line
• What is specular reflection?

  when a wave is reflected in a single direction by a smooth surface
• What is diffuse reflection?


  when a wave is reflected in lots of directions by a rough surface
• What are electromagnetic waves?

  vibrations of electric and magnetic fields meaning they can travel through vacuum
• What is the order of the EM waves from longest wavelength?

  • radio waves

  • microwaves

  • infra-red

  • visable light

  • ultraviolet

  • x-rays

  • gamma rays
• What is refraction?

  when a wave changes direction as it passes a boundary between two materials at an angle to the normal
• What does the amount of refraction depend on?

  how much the wave speeds up or slows down - depends on the density of materials (higher density, slower it travels)
• How can you produce radio waves?

  using an alternate current in an electrical circuit
• What is a transmitter?

  object which charges oscillate to create radio waves
• What are radio waves used for?

  communication
• What waves are used for bluetooth?

  radio waves
• What can microwaves do?

  pass easily through Earth's watery atmosphere
• What waves are used for satellites?

  microwaves
• How do microwaves work in a satellite?

  • signal from transmitter is transmitted into space

  • picked up by satellite receiver dish orbiting above Earth, transmits signal back to Earth in different direction

  • received by satallite dish on ground
• How do microwaves work in microwave oven?

  • microwaves are absorbed by water molecules in food

  • microwaves penetrate few cm before being absorbed and transferring the energy to water molecules - heats water up

  • water molecules transfer energy to rest of molecules in food by heating - quickly cooks food
• What is infrared raditation used for?

  increase or monitor temperature
• How can food be cooked using infrared radiation?

  temperature increases when food absorbs IR radiation
• How do infrared cameras monitor temperature?

  camera detects IR radiation and turns it into an electrical signal, displayed on screen
• How do electric heaters work?

  emitted IR radiation is absorbed by objects and air in room - energy transferred to thermal energy stores - causing temperature to increase
• What are optical fibres?

  thin glass or plastic fibres that can carry data over long distances as pulses of visible light
• How do optical fibres work?

  light rays are reflected so bounce back and forth until they reach the end of fibre
• What is fluorescence?

  property of certain chemicals, where ultraviolet radiation is absorbed and then visible light is emitted
• What are the uses of ultraviolet?

  • fluorescent lights - generate UV radiation and re-emit as visible light, they are more energy efficient

  • security pens - mark property with name, under UV light ink will glow, helps police identify stolen property

  • suntan - UV produced by sun can be used in tanning salons where UV lamps
• How are x-rays used in medicine?

  • see broken bones - passes through flesh but not through denser material like bones

  • used along side gamma rays to treat people with cancer, high doses of rays kill all living cells - directed towards cancer cells
• How are gamma rays used in medicine?

  used as medical tracer - gamma emitting source is injected to patient and progress is followed around body
• How do some EM radiation cause damage?

  • high frequency waves like UV, x-rays and gamma all transfer lots of energy - cause lots of damage

  • UV radiation damages surface cells, can lead to sunburn and cause skin to age

  • x-rays and gamma rays are types of ionising radiation - cause gene mutation or cell destruction and cancer
• What are the 3 rules for refraction in a convex lens?

  • incident ray parallel to the axis refracts through the lens and passes through principle focus

  • incident ray passing through principle focus refracts through lens and travels parallel to axis

  • incident ray passing through centre of lens carries on in same direction
• What are the 3 rules for refraction in a concave lens?


  • incident ray parellel to axis refracts through lens, travels in line with principle focus (appears to come from principal focus)

  • incident ray passing through the lens towards the principle focus refracts through lens and travels parallel to the axis

  • incident ray passing through the centre of then lens carries on in same direction
• What is a real image?

  A real image is formed when light rays converge and can be projected onto a screen
• Whats is a virtual image?

  when rays diverge, so light from the object appears to be coming from a different place
• How do you describe an image properly?

  • how big is it compare to object

  • upright or inverted

  • real or virtual
• What are the primary light colours?

  • red

  • green

  • blue