P5

• Waves 


  amplitude- displacement from rest position to crest or trough

  Wavelength- length of a full cycle

  Frequency- number of complete waves or cycles passing through a certain point per second (Hz)

  Period- number of seconds for a full cycle : 1 / frequency
• Transverse

  • vibrations are perpendicular (90 °) to the direction the wave travels
  • Most waves are transverse

  > Electromagnetic waves

  > S waves

  > Ripples and waves in water

  • travel on surface of a liquid but not through it
• Longitudinal waves

  • Parallel to direction the wave travels

  > Sound waves and P waves

  • compress and rarefaction - high pressure (lots of particles), low pressure (fewer particles)
• waves speed (m/s) = frequency (Hz) x Wavelength (m)
• 1khz = 1000 hz
• 1 Mhz = 1000000 Hz
• How to measure the speed of sound

  • Oscilloscope
• Measure frequency

  • cork and stop watch

  1. Float cork in ripple tank , bob up and down as wave pass it
  2. Start stop watch when cork is at the top
  3. Count how many times the cork bobs in a time interval
  4. Divide number by time interval
• Measure wavelength

  • use of strobe light

  1. place card behind ripple tank
  2. turn on strobe light and adjust its frequency until the waves appear to freeze
  3. measure the distance that no. of waves cover
  4. Divide the distance by number of waves
• Waves are:

  • absorbed- transfer energy to materials energy store
  • transmitted- carries on travelling through the material at a different speed which could lead to refraction
  • Reflect- sent back away from second material
• Reflection of light 


  Angles of incidence = Angle of reflection

  • reflection of visible light allows us to see as light reflects back into our eyes
  • rough surfaces scatter the light
  • White light is a mixture of different colours which have different wavelengths
  • All colours in white light is reflected at the same angle so white light doesn't split into different colours
• Refraction

  • wave travels at different speed in materials with different densities
  • frequency stays the same when it crosses boundaries
  • waves hitting boundaries at an angle- changes speed, it bends
  • greater change of speed the more it bends (refraction)
  • If wave slows down it bends to the normal
  • sound travels faster in denser materials
  • EM waves travel slower in denser materials
• Colours and refraction

  • travel at different wavelengths
  • shortest to longest: violet, indigo, blue, green, yellow, orange, red
  • travel at same speed in air but short wavelength slow down in denser materials and bend more
• Specular reflection

  • waves are reflected in single direction by a smooth surface giving a clear reflection
• Scattered reflection

  • reflected on rough surface
  • reflected in different directions
  • due to the normal being different for each incident ray
  • Surface looks matte and don't give clear reflection
• investigate reflection using ray box and mirror

  1. draw solid line and dotted line (normal)
  2. Use a plane mirror and line up to solid line
  3. use ray box, shine thin beam of white light at mirror so light hits mirror where normal meets mirror
  4. trace incident and reflected light rays
  5. measure angle between incident ray and normal and the angle between the reflect ray and the normal using a protractor
  6. repeat steps, vary angle of incidence
• Ray diagrams for refraction

  1. draw normal where any ray meets a boundary
  2. light ray travelling into a more dense material will slow down making it bend towards the normal
  3. of light ray is travelling to less dense material it will speed up making it bend away from the normal
  4. if light ray is travelling through a rectangular block, the emerging ray and the incident ray will be parallel

  • Angle of incidence is between incident ray and normal
  • Angle of refraction is between the refracted ray and the normal
  • Shorter the wavelength the more it refracts
• Triangular prism

  • different wavelength (colour) of light travels at different speeds in glass so they refract at different amounts
  • when lights passes through prism you get a rainbow

  1. light bends towards the normal as it enters prism
  2. glass is denser than air
  3. different wavelength of light bend by different amounts

  Red- the least

  Violet- the most

  2. Light bends away away from the normal as it leaves the prism, due to shape different colours bend at different amounts - spreads the awareness

  3. gives off light spectrum
• Sound waves

  • caused by vibrating objects
  • passed through surroundings as a series of compressions and rarefactions
  • when a sound travels through a solid causes vibrations of the particles in the solid
  • air passes on the vibrations
  • sound waves travel at different speeds in different media- faster in solids than in liquids, and faster in liquids than in gases
  • Frequency doesn't change when it passes from one medium to another
  • Wavelength does change- It gets longer as it speeds up, and shorter as it slows down
  • sound waves are reflected by hard flat surfaces
• • Sound waves can't travel in space as its a vacuum
• Hear sound

  1. sound waves reach eardrum causing it to vibrate
  2. vibrations passed on to tiny bones in your ear (ossicles), through semicircular cancel and to the cochlea
  3. Cochlea turns vibrations into electrical signals which get sent to brain
  4. Brain interprets signals as sounds of different pitches and volumes, depending on frequency and intensity
  5. high frequency - higher pitch
  6. Human hearing is limited by the size and shape of eardrum and structures of all the parts within the ear to vibrate to transmit the sound wave

  • bad hearing due to wear and tear of cochlea or auditory nerve
• Ultrasound

  • partial reflection
  • see hidden things
  • Pass through the body and partially reflect at boundaries between different tissues
  • know the speed of ultrasound in the different tissues, calculate distance to the different boundaries
  • reflections are processed through a computer to produce an image
  • ultrasound can be used to form an image of a developing foetus and to examine soft tissues and organs
  • Completely safe
  • Can be used to find flaws
• Sonar

  • find distance to the seabed or to locate objects in deep water
• EM waves

  • transverse waves
  • travel at same speed through air and vacuum but different in different materials
  • vary in wavelength, shorter wavelength have higher frequencies
  • EM waves transfer energy from a source to an absorber
  • the higher the frequency of the EM wave, the more energy it transfers
• Radio waves 


  10$^4$ m - 1m

  • longest wave length, smallest frequency
  • generate using electricity of alternating currents
  • Oscilloscope sees frequency oh A.C of waves to transmitter
  • Receiver absorbs the energy and oscilloscope sees same frequency
  • Allows to transfer information
  • long waves- huge distance diffract around curve of earth
  • short wave- travels long distance, can't curve around earth, reflect from ionosphere
  • Very short waves- t.v and fm radio- directly from transmitter to receiver
• Microwave 


  10$^-2$m

  • long wavelength, low frequency
  • two types: absorbed/ not absorbed by water molecules

  Not absorbed:

  • satellites - pass through atmosphere and received by satellites and transmitted back to earth to satellite dish

  Absorbed

  • microwave- heat up food, water molecules vibrated and transfers energy to neighbouring molecules
• Infared 


  10$^-5$m

  • emitted from all objects that heave thermal energy
  • thermal cameras- to see in there dark
  • Cooking- heats foods by transferring the heat energy- doesn't penetrate food
  • Electric heaters- electrical energy to heat metal which emits infrared to environment
  • Harmful in high quantities
• Visible light 


  • red, orange, yellow, green, blue, indigo, violet
  • Optical fibres- thin glass/plastic, cary data over long distances as pulses of light - work by bouncing light off the side of narrow core as It enters core at certain angle at one end and is reflected again and again till it emerges

  Used for: telephone and internet cables and medical purposes to see inside the body

  10$^-7$
• ultraviolet 


  • fluorescent- ultraviolet absorbed and energy re-emitted as visible light
  • fluorescent light- generate uV radiation, absorbed by a layer of phosphorus and re-emits as visible light
  • security- mark property that are invisible until you shine uv light

  10$^-8$
• X-rays


  • short wavelength, highest frequency
  • View internal structure of objects
  • absorbed by dense materials and passes through mostly air and partially though fleshy part
  • detect broken bones - small amount that's worth to take the risk
  • Danger for staff, need to wear lead
  • mostly transmitted by tissue, absorbed by denser materials
  • Absorption happens too and can produce high resolution images

  10$^-10$
• Gamma rays

  • 10 - 15
  • Smaller wavelength, biggest frequency
  • sterilise medical equipment and food
  • kill microorganisms without causing other damages
  • keeps food fresh for longer and safe to eat
  • transmitted by skin, soft tissue and bones
  • radio tracers are radioactive isotopes that patients either swallow or injected- often part of a molecule see where the tracer ends up
• Where do EM waves come from

  Gamma - radioactive decay

  Ultraviolet, X-ray, VL - electrons drop down energy levels

  Infared- bonds holding molecules together vibrate
• Disadvantages of X-rays and gamma rays

  • ionising radiation
  • can damage cells
• Colour and transparency

  • colour- different in absorption, transmission and reflection of different wave;engths by different materials
  • white light- mixture of all colours
  • opaque- do not transmit light - absorb some wavelengths and reflect others
  • black- absorbs all wavelengths of visible light - lack of bistable light
  • Transparent- and transluscent- transmit light
• Colour filters

  • filter out different wavelengths of light - so some are transmitted and rest absorbed
  • primary colour filter only transmits that colour
  • Different filter on specific colour would turn black as all light is absorbed
  • non primary colour filters let out light wavelengths of light corresponding to the colour
• real image

  • light from an object comes together to form an image on a 'screen'
• Virtual image

  • rays are diverging- light seems to come from different place
• Concave (diverging)

  • caves inwards
  • causes parallel rays of light to diverge (spread out)
  • principal focus of a concave lens is when rays hit the lens parallel to the axis appear to come from
• Convex (converging)

  • bulges outwards
  • causes parallel rays of light to coverage (move together)
  • Principal focus- where rays hitting the lens parallel to the axis all meets
• Focus length

  • distance from centre of the lens to principal focus