# G482 Waves

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## 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. 3 of 11

## intensity spectrum

• Continuous spectrum contains all the wavelengths.
• Area= total energy emitted by the source 4 of 11

## 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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## polarisation

• 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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## Reflection

• 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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## Refraction

• 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

• 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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