Yr9 Physics - Waves (GCSE AQA P1.5.1 - P1.5.3)

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• http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/waves/

1. General Properties
   1. WAVES: a transfer of energy as a result of the vibrations/oscillations of particles
   2. Waves are either transverse or longitudinal
      1. TRANSVERSE: wave oscillations are perpendicular to direction of wave transfer
         1. electromagnetic waves are transverse
            1. infrared radiation
            2. light waves
            3. microwaves
            4. X-rays
            5. radio waves
            6. gamma rays
            7. ultraviolet/UV waves
      2. LONGITUDINAL: wave oscillations are parallel to direction of wave transfer
         1. sound waves
         2. longitudinal waves show areas of compression and rarefraction
      3. mechanical waves are either transverse or longitudinal
         1. water waves (transverse)
         2. seismic waves (transverse)
   3. Electromagnetic waves for a continuous spectrum called the Electromagnetic Spectrum
   4. Electromagnetic waves can travel through a vacuum because they don't need particles to transfer energy whereas mechanical waves can't because they need particles to transfer energy
      1. all electromagnetic waves travel at the same speed in a vacuum
   5. Waves can be reflected, refracted and diffracted
   6. Waves undergo a change of direction when they are refracted at an interface
   7. The terms frequency, wavelength and amplitude.
   8. All waves obey the wave equation: wave speed = frequency x wave length
   9. Radio waves, microwaves, infrared and visible light can be used for communication.
2. Reflection
   1. The normal is a construction line perpendicular to the reflecting surface at the point of incidence.
   2. The angle of incidence is equal to the angle of reflection.
   3. The image produced in a plane mirror is virtual.
   4. Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirrors when light waves hit them. The waves are reflected uniformly and light can form images The waves can:
      1. appear to come from a point behind the mirror, e.g. a looking glass
      2. be focused to a point, e.g. sunlight reflected off a concave telescope mirror
   5. Rough surfaces scatter sound and light in all directions. However, each tiny bit of the surface still follows the rule that the angle of incidence equals the angle of reflection.
   6. REFLECTION: the change in direction of a wave once striking the boundary between two mediums
3. Refraction
   1. REFRACTION: the change in direction of a wave once it passes across the boundary from one medium to another of varying density
   2. Refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal) - they carry straight on.
   3. PATTERN 1: The wave slows and its wavelengths decreases as it passes the boundary of the new medium. As the wave leaves the new medium and passes the boundary into the first medium, its speed and wavelengths return to their original values
   4. PATTERN 2: if the light ray hits the boundary at an angle, its speed and direction changes. The light ray is bent back into its original direction as it leaves the new medium.
   5. PATTERN 3: As the ray goes into the new medium from the air, it bends towards the normal. The angle of refraction is less than the angle of incidence.
4. Diffraction
   1. DIFFRACTION: When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap.
   2. The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap.
      1. a gap similar to the wavelength causes a lot of spreading with no sharp shadow, eg sound through a doorway
      2. a gap much larger than the wavelength causes little spreading and a sharp shadow, eg light through a doorway.
5. Ray Diagrams
   1. In a ray diagram, the mirror is drawn a straight line with thick hatchings to show which side has the reflective coating. The light rays are drawn as solid straight lines, each with an arrowhead to show the direction of travel. Light rays that appear to come from behind the mirror are shown as dashed straight lines.
   2. Make sure that the incident rays (the solid lines) obey the law of reflection: the angle of incidence equals the angle of reflection. Extend two lines behind the mirror. They cross where the image appears to come from.
   3. The image in the plane mirror is:
      1. virtual (it cannot be touched or projected onto a screen)
      2. upright (if you stand in front of a mirror, you look the right way up)
      3. laterally inverted (if you stand in front of a mirror, your left side seems to be on the right in the reflection)
6. Wavelength
   1. WAVELENGTH: the distance between a point on one wave and the same point on the next wave.
   2. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.
7. Frequency
   1. FREQUENCY: the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second.
   2. Unit of frquency
      1. Hz = Hertz
      2. kHz = Kilohertz
      3. MHz = Megahertz
      4. GHz = Gigahertz
   3. the frequency of sound waves decides whether it is high or low in pitch
   4. the frequency of light waves decides what colour we see
   5. Frequency of light:
      1. (infrared) Red Orange Yellow Green Blue Indigo Violet (ultraviolet)
      2. low frequency of light --> high frequency of light
8. Wave Speed
   1. WAVE SPEED: how far the wave travels forward (propogate)
   2. measured in metres per second = m/s
   3. speed determined by the material or medium the wave is travelling through
   4. v is the wave speed in metres per second, m/s
   5. f is the frequency in hertz, Hz
   6. λ (lambda) is the wavelength in metres, m
   7. v = f × λ
9. Amplitude
   1. As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position.
   2. AMPLITUDE: the size of the wave
   3. the amplitude of sound waves decides whether it is loud or quiet
   4. the amplitude of light waves decides whether it is bright or dim
10. Sound
    1. Sound waves are longitudinal waves that must pass through a medium
       1. Echoes are reflections of sounds
       2. Their vibrations occur in the same direction as the direction of travel
       3. Sound waves can only travel through a solid, liquid or gas
    2. When an object or substance vibrates, it produces sound:
       1. the greater the amplitude, the louder the sound
       2. the greater the frequency, the higher the pitch
    3. Human hearing
       1. Range of human hearing is between 20 Hz and 20 kHz
          1. range decreases with age
       2. Sounds with frequencies above ~20 kHz are called ultrasound
11. Light/Electromagnetic Spectrum
    1. Light and other forms of electromagnetic radiation travel as transverse waves
    2. These waves can travel through a vacuum, and they all travel at the same speed in a vacuum
    3. ELECTROMAGNETIC SPECTRUM: a continuum of all electromagnetic waves arranged according to frequency and wavelength.
    4. long wavelength + low frequency --> short wavelength + high frequency
       1. Radio waves Microwaves Infrared Visible Light Ultraviolet X-rays Gamma rays
    5. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency
    6. White light can be split up using a prism to form a spectrum. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum
    7. Visible light is just one type of electromagnetic radiation. There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light
    8. Radio waves have the lowest frequencies and longest wavelengths, while gamma waves have highest frequencies and shortest wavelengths
    9. The wavelengths vary across the electromagnetic spectrum from about 10–15m to more than 104m
12. Electromagnetic Wave Creation, Use & Dangers
    1. Radio waves
       1. DANGERS: cause cancer, leukaemia and other disorders
       2. USES: radio and television signals
       3. CREATION: types of transmitters, stars, sparks and lightning
    2. Microwaves
       1. DANGERS: cause cataracts (clouding of lens) and affects part of the brain during phone use
       2. USES: cooking, mobile phones, satellites, speed cameras and radars
       3. CREATION: types of transmitters and stars
    3. Infrared radiation
       1. USES: remote controls, heal sport injuries, alarm systems, thermal imaging and weather forecasts
       2. DANGERS: overheating
       3. CREATION: hot objects, stars, lamps, flames and bodies
    4. Visible light
       1. CREATION: anything hot enough to glow
       2. USES: seeing things, photography, compact discs, DVD players, laser printers and weapon aiming systems
       3. DANGERS: damage to the retina cause by looking at too much light
    5. Ultraviolet
       1. CREATION: special lamps and the Sun
       2. USES: getting a sun tan, detecting forged bank notes, killing microbes, sterilisiing products and bodily production of vitamin D
       3. DANGERS: damage to retina, cause sunburn and cancer
    6. X-rays
       1. CREATION: stars and X-ray machines
       2. USES: see inside people (inspect bones, etc.), airport security and astronomy
       3. DANGERS: cause cell damage and cancers
    7. Gamma rays
       1. CREATION: stars and radioactive waves
       2. USES: radiotherapy (killing of cancer cells), kill microbes, sterilise food and medical equipment
       3. DANGERS: cause cell damage and mutations in growing tissues