G482 Waves



Progressive Waves

  • Progressive waves transfer energy, without any net transfer of matter.
  • When a wave oscillates it transmits energy from one place to another.
  • A wavelength is the distance between two points that are in phase, e.g 2 peaks or 2 troughs.
  • With time on the x axis, it changes to period between 2 points.
  • f=1/T (Hz)
  • Only waves of the same type can interfere with eachother

Wave speed

  • Frequency is the number of waves to pass a point per unit time.
  • v=f(lambda)
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Different vibrations

  • Waves can be transverse or longitudinal
  • For transverse- vibrations are perpendicular to the direction of travel of the wave energy e.g light energy
  • For longitudinal - vibrations are parallel to the direction of travel of the wave energy e.g sound waves.
  • Where particles are compressed theyre called compressions and when spread out theyre called rarefactions
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wave instensity

Wave intensity

  • Intensity is the amound of wave energy per unit are per unit time
  • I=P/A (wm^-2)
  • I=P/4pi^2 for radial point sources
  • I =1/d^2
  • Double the distance, intensity will fall to a quarter of initial value.Image result for intensity distance graph
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intensity spectrum

  • Continuous spectrum contains all the wavelengths.
  • Area= total energy emitted by the source(http://hsc.csu.edu.au/physics/options/astrophysics/3034/blackbody.gif)
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intensity and amplitude

  • Distance is twice the amplitude
  • Doubling the amplitude with same frequency, the distance doubles, average speed doubles.
  • Kinetic energy quadruples as its proportional to v^2 and intensity quadruples.
  • Intensity is proportional to energy and therefore intensity is proportional to amplitude^2.
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  • Plane polarised: Vibrations are confined to one plane only.
  • Only transverse waves can be polarised
  • Light can be polarised, sound no, radiowaves yes
  • Unpolarised light has vibrations in all planes perpendicular to direction of travel
  • polaroids polarise light
  • If the angles of the polariser and analyser are parallel, then all the transmitted light will pass through.
  • If they're perpendicular to eachother, the analyser will absorb all the polarised light.
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polarisation pracital applications

  • Reflected light from non-metallic surfaces is partially polarised, polarised sunglasses reduce glare.
  • You can enhance reflection in photography by aligning the polaroid filter with the polarised light.
  • Radio waves and microwaves, antannae produce and receive plane polarised waves.
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  • Wavefronts represent peaks.
  • Distance between wavefronts is lambda
  • Take average e.g 6 waves divided by 6
  • Wavefronts are perpendicular to incident ray.
  • Draw the normal, all angles measured from it.
  • Incident angle equal to reflected angle
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  • Wave change in speed as it crosses from one medium to another.
  • Change in direction if there's an angle between incident wave and normal
  • Light will refract towards the normal line as it enters and wavefronts are closer since it slows down so wavelength decreases since frequency remains constant.
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Refraction types

  • Light refracts towards the normal and slows down
  • Mechanical waves(sound) if it travels into a more dense medium, it refracts away from normal and speeds up.
  • Water wave into shallower water refracts towards normal and slows down
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  • Diffraction is the spreading out of waves as they pass through a gap or around a corner.
  • When the gap = size of wavelength there's maximum diffraction.
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