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Heat, light, and sound (sound (hearing sounds (cochlear implant (bionic…

- - - - particles push apart, substance expands
        
        if enough energy, particles break free --> change state
  - - - absolute zero (-237): when particles do not move at all
    - - alcohol/mercury inside tube expands/contracts in response to temperature
  - - - e.g.
      - more water = more total energy, even though same temperature
  - - - direct flow of heat between materials in direct contact
      - vibrating particles pass on vibration --> pass on heat
      - e.g. vibration particles in soup bump into particles of spoon --> make spoon hot
      - conductors: metal, glass
      - insulators: plastic, air, cloth, cork, wood, rubber, gas
      - gas: trapped in cotton/feather/wool/polyester of coats, donnas, etc --> keeps you warm
    - - convection current: warm air less dense, pushed upwards --> cools, sinks --> heated again, rises
        
        spreads heat around area
      - liquids and gases (movable particles)
      - sea breeze (day): from the sea towards land
      - land breeze (night): from the land towards sea
    - - transmits heat as invisible waves at speed of light (300 000km/s)
      - can travel through vacuum (no particles)
      - infrared radiation transmitted this way - all objects emit some infrared
      - e.g. heat from sun
      - the hotter the object, the more heat is radiated
      - when radiation heats surface
        
        absorption: dark colours
        
        reflection: light colours
        
        transmission: clear materials
        
        e.g. dark-coloured car heats up faster than lighter car
- - - - creates sound wave (series of alternating compressions and rarefactions)
        
        travel away from source like ripples in pond
        
        solid/liquid/gas is needed for transmission
  - - - particles move perpendicular to actual wave
    - - particles move in same direction as actual wave
  - - - more closely packed particles, faster sound is transmitted
      - fastest solids, slowest gases
    - - warmer materials have faster vibrating particles
        
        the warmer the material, the faster sound travels
  - - - measures time difference between sending and receiving signals
  - - - e.g. used in concert halls
  - - - young people up to 20 000 Hz
      - 65+: up to 5000 Hz
      - ultrasound: sound waves with frequencies over human range
        
        pass easily through fluids and soft tissue, reflected from other layers within organ/foetus
        
        echoes detected and analysed to create 3D image
      - infrasound: sound waves with frequencies below human range
  - - - changing length alters frequency of sound
      - longer the string, slower the vibration, lower the frequency and pitch
    - - skin vibrates when hit
      - instrument itself vibrates when hit
    - - column of air vibrates
      - length adjusted by covering holes
      - longer column = lower pitch
  - - - causes of hearing disabilities
        
        ear canal blocked with wax
        
        middle ear filled with fluid
        
        ruptured eardrum (due to infection or loud noise)
        
        sensory cells damaged (due to loud noise)
        
        defect in auditory nerve or tiny hairs of cochlea --> sound impulses not transmitted to brain
      - Australian
      - developed in 1970s by Professor Graeme Clark
      - converts sound into electrical impulses
      - over 1 million australians have hearing disability
- - - - Travels at around 3 x 10^8
        
        Or 300 000 km/s
    - - Reflected off it
      - Transmitted through it
      - Absorbed into it
      - This depends on the material
        
        Transparent
        
        almost all light is transmitted through it
        
        A clear image can be seen through it
        
        E.g.
        
        Clear glass, shallow water
        
        Translucent
        
        Some light may be reflected
        
        Light that passes through is scattered
        
        An image seen through it is fuzzy
        
        E.g.
        
        Issue paper, frosted glass
        
        Opaque
        
        light is either reflected from or absorbed into the substance
        
        No light is transmitted
        
        No image can be seen through it
        
        E.g.
        
        Brick, football
    - - We see these because light bounces off them and into our eyes
  - - - When light bounces of a smooth object such as a mirror
      - Creates an image
    - - When light bounces of a rough surface, scattering it
      - Does not produce an image
  - - - The image is flipped sideways
    - - virtual image produced by plane mirror looks as if it is really positioned inside
      - because your brain is used to light travelling in straight lines --> automatically extends light back inside mirror
      - virtual images are:
        
        upright
        
        same size as object
        
        laterally (sideways) inverted
        
        seen in plane mirror
        
        appears same distance inside mirror as actual object
  - - - Light takes different times to travel through different substances
        
        Takes longer through denser objects
        
        Takes less through less dense objects
        
        This results in different amounts of bending, or refraction, as light passes from one substance into another
    - - light from an object under water is bent away from the normal when it leaves water and enters air
      - brain traces light back in straight line --> object appears to be closer to surface
      - actual depth vs apparent depth
    - - The measure of how easily light travels through a substance
        
        The smaller the refractive index, the ‘faster’ light will travel through it
        
        The longer the refractive index, the ‘slower’ light will travel through it
    - - when light enters substance of lower refractive index --> refracted away from normal
      - critical angle: angle of incidence where light is refracted so far away from normal that it runs along boundary of two substances
      - total internal reflection: for angles of incidence higher than this, there is no refracted ray --> light reflected from boundary like a mirror
      - e.g. diamonds sparkling
        
        diamond has high refractive index and low critical angle (23 degrees)
        
        cut so that light will strike at higher than critical angle
        
        light is reflected twice within diamond before it emerges
    - - A transparent piece of plastic, glass or jelly that is shaped to curve inwards or outwards
      - A lens refracts light and focuses it to form images in the eye and in devices such as cameras, telescopes etc.
      - Convex lenses
        
        A lens that bulges outwards
        
        Cause light rays to come together, or converge
        
        If a convex lens is held close to an object, it can be used as a magnifying glass
        
        Upright
        
        Enlarged
        
        Virtual image
      - Concave lenses
        
        A lens that curves inwards
        
        Causes light rays to diverge, or spread out
        
        Image
        
        Small
        
        Upright
        
        Virtual
        
        Focal point behind lens