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Wave InterferenceJ. Tobler
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What is a Wave?A disturbance that carries energy through
matter or space.They carry energy without transporting matterWaves can do work!
Most move through a medium (matter wave travels through)Mechanical Waves need a medium to transfer
the energyElectromagnetic waves do not need a medium,
they can travel through empty space
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Where do waves come from?Most waves are caused by vibrating
objectsStrings on a guitarEardrum SpringsCharged particles (in light waves)
Exist only as long as it has energy to carry
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Wave VocabularyCrest – high point of a waveTrough – low point of a waveRest position – mid point between crest
and troughAmplitude – distance from rest position to
crest or trough, depends on energyNodes – points where wave crosses rest
positionWavelength (λ) – distance between to
common points on a wave (crest to crest), depends on frequency
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Anatomy of a Transverse Wave
Wavelength
()
Nodes
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FrequencyHow oftenRepresented as fMeasured in Hertz (Hz)High frequency = short wavelength and vice versa
Inversely related to the period (f = 1/T)
f = # waves / total time
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PeriodThe time to complete one cycle or
oscillationRepresented as TMeasured in seconds (s) Inversely related to frequency
(T=1/f)With a low frequency, the time between cycles is greater because the waves don’t pass by as often.
T = total time / # waves
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Wave SpeedOr wave velocity
How fast the energy moves through the medium
Depends on the frequency and wavelength
Wave speed depends on the mediumV= f λ
λ = wavelength (m)
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Which set of waves has the highest frequency?Which set of waves has the shortest period?Which set of waves has the longest wavelength?Which set of waves has the greatest amplitude?
10 seconds
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What happens to a wave when it reaches a boundary?
It will either pass through or reflect the energy depending on the density of the mediums.
If the boundary is very dense and rigid then the wave will just reflect reversing its direction.
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When Waves CollideWaves interfere with each otherConstructive Interference
Amplitudes are in the same direction, or “in phase”
Waves add together creating a greater amplitude
Interference is temporary
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Constructive Interference
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When Waves Collide (Part 2)Destructive Interference
Amplitudes are in opposite directions or “out of phase”
Waves cancel each other out resulting in a smaller amplitude or zero amplitude
Also temporary
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Destructive Interference
Notice what happens to the blue wave as the others go in and out of phase with each other.
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Standing WavesResult of Constructive and Destructive
Interference caused from wave reflection at fixed boundaries
Video LinksConstructive vs Destructive InterferenceStanding Waves ExplainedWave InterferenceStanding Waves and Strobe LightStanding Wave Demonstration with high speed
camera
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Parts of a Longitudinal or Compression Wave
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Transverse vs. Longitudinal Waves
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Properties of Waves SummaryType of Wave Mechanical Electromagnetic
FormLongitudinal Transverse Modeled as transverse
Medium Solids, liquids, gases
Solids and liquids
None required
Travel asCompression and rarefactions in matter
Back-and-forth (or up-and-down) movement of matter
Oscillating electric and magnetic fields
Examples Sound waves, some earthquake waves
Water waves, rope waves, some earthquake waves
Visible light waves, radio waves, x-rays