Waves

Waves

1. Wave properties

   • regular disturbance that carries energy
   • Direction of wave
     • Transverse
       • Light + Water
     • Longitudinal
       • Sound
   • Use of particles
     • Mechanical
       • vibrating particles through a medium
     • Electromagnetic
       • travel through a vacuum

2. Reflection

   • incidence = reflection

3. Refraction

   • Into more dense area
     • incidence > reflection
     • Bends towards the normal
   • Into less dense area
     • incidence < reflection
     • Bends away from normal

4. Describing waves

   • Amplitude
     • maximent displacement from undisturbed position
   • Wavelength
     • distance between two equivalent points on two waves
   • Frequency
     • number of waves to pass a point per second
   • Period
     • Frequency (Hz) = 1 / Period (s)
     • How long it takes for a wave to pass a single point
   • Wavespeed (m/s) = Frequency (Hz) x Wavelngth (m)

5. Electromagnetic waves

   • Visable spectrum
     • Uses
       • Film camera
         • light focused on a light sensitive film
       • Digital camera
         • Light focused on a sensor
   • Infa - red
     • Source
       • All objects
       • Hotter the object, the more infa - red is produced
     • Penetration
       • Absorbed by skin
     • Uses
       • Optical fibres
         • thin glass fibres
         • radiation can not escape the fibres
         • Transmits a signal
       • Remote control handsets
       • Medicinal scanners
       • Thermal imaging cameras
   • Microwaves
     • Uses
       • communications
         • passes through atmosphere reching satellites
       • Heating food
         • Penetrates food, absorbed by water therfore heats food
   • Radiowaves
     • 300, 000 => 3000 million Hz
     • Hazardous
     • Uses
       • Wavelength < 1m
         • TV broadcasting
       • 1< Wavelength<100m
         • Local raio
       • Wavelength > 100m
         • International radio stations
       • Mobile phones
         • Information carried between phone and nearest phone mast
   • Audio transmissions
   • Ultra-violet
     • Some chemicals emit light when they absorb UV
     • Hazards
       • Can cause blindness
       • Harmful to skin
         • Premature ageing
   • X- rays
     • Straight through most substances
     • Produced when electrons are stoppd
     • Uses
       • Detects cracks in metal objects
       • X-rays in medicine
         • X-rays for imaging have less energy for those used for therapy
   • Gamma Rays
     • Produced when unstable isotopes release energy
     • Uses
       • Killing cancr cells
       • Kills harmful bacteria
         • Prevents food from spoiling
         • Surgical instruments

6. Sound waves

   • Amplitude
     • Loudness
   • Frequency
     • Pitch
   • Ultrasound
     • Higher frequency than 20 000hz
     • Two different media between reflected
       • Time taken between reflections can determine how far away a boundary is
       • Collected and interpretated as an image
     • Medical
       • Gel is used to reduce the amount of wave reflected
         • 99.9% reflected otherwise
     • Industrial

7. Seismic waves

   • Seismograph
     • Detects movement in the Earth's crust
     • Seismogram
       • What it is recorded on
   • Primary waves
     • Longitudinal waves
     • Travels through solids and liquids
     • Travels slower
   • Secondary waves
     • Transverse
     • Travels through solids
     • Travels slower

8. Heat transfer by radiation

   • Matt Black => Silver - best => worst emmitor / absorber
   • Thermal radiation
     • Infa-red
   • Hotter object = emits more infa-red

9. Black body radiation

   • Black body
     • Absorbs all radiation
     • Sun
   • The hotter an object, the shorter the peak wavelength
     • Area under curve = energy

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