Waves

• waves

  Transfer energy (no matter) from one place to another

  vibrate (oscillate) to move vibrations

  amplitude = displacement from equilibrium point

  wavelength = one entire oscillation

  time period = time for one complete oscillation

  frequency = Hz = 1/t
• Wave speed

  Wave speed = frequency x wavelength

  V = f x lambda
• Transverse waves

  Oscillations are perpendicular to energy transfer (up and down on oscilloscope)

  e.g light, radio, electromagnetic and ripples
• Longitudinal waves

  Oscillations are parallel to energy transfer (compression and rarefraction )

  e.g sound and seismic P waves
• Reflection


  Shown by ray diagrams

  normals always 90 degrees

  angle of incidence = angle of reflection

  Specular reflection = reflected off a flat surface normals are all in same direction

  diffuse/scattered reflection = reflected of a bumpy surface normals are all in diff directions
• Refraction


  When waves change direction as they pass from 1 medium to another

  light refracts as waves travel at diff speeds in diff materials as they have diff densities

  high density = slower light travels= bends towards normal

  lower density = faster light travels= bends away from normal
• EM waves 


  All transverse waves + in a vacuum all travel at 3 x10 to the 8 m/s

  wavelength an frequency are inversely related

  come from everywhere e.g radioactive decay
• Radio waves


  Longest wavelength

  lowest frequency

  use transmitter and oscilloscope to see frequency of a.c and determine frequency of wave

  detect again by receiver

  this allows us to transfer information
• Uses of radio waves


  Communications

  long wave = huge distances covered for long distance communication

  short wave = long distances, reflected of ionosphere to travel or used for Bluetooth

  Very short waves = transmitted and receiver like TV and remote
• Microwaves


  Relatively long wavelength and low frequency

  absorbed by water = used in microwave ovens to heat water molecules in food to heat it up with energy via convection/conduction

  aren’t absorbed by water = used for satellite as aren’t stopped by atmosphere
• Infrared waves


  Relatively long wavelength and low frequency

  emitted from all objects that have thermal energy

  used in infrared cameras to see in dark e.g spot living organisms

  hot =bright cold = darker

  used in cooking by heat metal to emit lots of infrared to heat food and cook it (doesn’t penetrates the food)

  or for electrical heaters which get so hot it emits infrared
• Microwaves and infrared waves

  Only dangerous in high quantities so background radiation isn’t bad but can burn in high quantities
• visible light


  We use it to see and depending on wave length determines colour so red is longest and violet shortest

  used for communication w optical fibres (thin glass or plastic that reflects pulses of lights along it = transmits data quickly

  • needs to be speculate reflection
  • optical fibres can transfer much more data than copper wires + electricity
• Ultra violet waves


  -Have shorter wavelength than visible light

  -up emitted from sun or generated like in sun-beds

  -used for fluorescence where uv light is absorbed and energy reemitted as visible light

  +fluorescent lights generate up and absorbs it in a layer of phosphorous that re emitts the energy as visible light
• Benefits of fluorescent bulbs

  Energy efficient so saves on electricity bills and environmental factors
• Security and UV


  Use special pens u can mark property and codes which are totally invisible until UV is shone on them

  used in passports and bank notes so forgeries can be detected
• X rays 


  Short wavelength but higher frequency (ionising)

  help us see internal structure of objects by firing x rays through object and recording ones that pass through on a detector plate = this is because it’s absorbed by dense material e.g bones and passes through less dense material e.g lungs + intestine

  images start white + go black when x rays are detected

  quick + cheap test + not at risk cus of low doses of radiation
• Gamma rays


  shortest wavelength and highest frequency

  Used for medical imaging and treat cancer and sterilisation: medical equipment and food, as it can kill micro organisms without causing any other damage (other option for equipment is boiling water but can’t always be used)
• x rays and gamma in medicine

  Both are ionising radiation which can damage cells and lead to cancer

  but also help treat and diagnose diseases so often have to say up pros and cons
• Lenses


  all lenses have a principle focus(focal point) on each side equal length apart

  Convex (converging) lens: refract light inwards to principle focus

  Concave lens: refract parallel rays of light outwards (disperse)

  distance between principle focus and centre of lens is focal length : shorter focal length = more powerful lens
• Real vs virtual images


  images are formed at a point where all light rays from a particular point on an object appear to come together

  Real: inverted, can be captured on a screen

  virtual: upright, can’t be captured on screen

  images can be described as magnified or diminished
• Visible light + colour 


  Objects appear certain colour depending on wavelength of light hitting it and properties of object

  Opaque = don’t transmit any light only absorb or reflect

  transparent = pass early all of light through

  translucent = pass some light through + colour depends on which wavelength transmitted most
• Colour filters


  Used so only certain wavelengths pass through so transmit some through whilst absorbing the rest

  filters for primary colours only let red green and blue through

  filters for other colours let that colour through and which ever primary make it e.g yellow also lets through green and red
• Radiation + temperature


  Hot objects = more emitted less absorbed = slowly cools

  cool objects = more absorbed less emitted = slowly heats

  if equal = stays same temp
• Intensity


  Power of radiation per unit of area
• Radiation emission graph


  Intensity on y axis

  wavelength on x axis

  As temperature of object increases so does intensity of every emitted wavelength
• Balance of absorption/emission of earth

  Absorbs radiation from sun

  emits infrared back out into atmosphere

  during day more is absorbed than emitted

  but at night less is absorbed than emitted
• Sound waves


  Vibrations passing through molecules of a medium

  longitudinal - compression and rarefaction

  in solids = cause particle to vibrate and pass on transmitting sound wave

  higher density = travels faster so travels fastest in solids

  (frequency doesn’t change only wavelength increases in high density)
• Human ear 


  Ear canal - sound waves travel along

  ear drum - hit and cause it to vibrate

  ossicles - vibrations pass along

  semicircle canals - vibrations pass along

  cochlea - converts vibrations into electrical signals

  auditory nerve -sends signals to brain for it to interpret them as sounds

  human ears can hear from 20 to 20,000 Hz but decreases due to age
• ultrasound


  Sound that vibrates at frequencies above 20,000 Hz (above human hearing) which some animals can use e.g bats

  humans produce it electrically

  when it hits a boundary between diff mediums some is refracted and some reflected = partial reflection

  completely safe
• Ultrasound - prenatal imaging


  Ultrasound machine used to scan foetuses as it transmits and receives the ultrasound waves and detects and processes when it passes through diff mediums
• Ultrasound - industrial screening

  Fire ultrasound waves at objects and should pass straight through if nothing is wrong (only partially reflected at start and end)

  if a crack the waves are reflected back and can detect the fault
• Ultrasound - sonar


  Fire waves at floor and receives them back to workout distance

  d = s x t

  but also have to halve as it is there and back
• Seismic waves


  P waves : longitudinal, travel through solids and liquids, much faster than S waves

  S waves : transverse, travel only through solids

  detected by seismometers by seismologists and work out how long it took for the waves to reach parts of earth

  The waves can be reflected and refracted when change mediums e.g between mantle (solid) and outer core (liquid) - only p waves