Superposition and Coherence
- Created by: Laylalink27
- Created on: 30-04-17 12:18
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- Superposition and coherence
- Constructive or destructive interference depends on path difference
- Path difference: how much farther one wave has travelled than the other
- An equal distance from both sources will cause constructive interference.
- Constructive interference occurs where path difference is whole number of wavelengths.
- If path difference is an odd number of half wavelengths, waves are out of phase and you get destructive interference
- path difference=n.lambda
- Constructive interference occurs where path difference is whole number of wavelengths.
- An equal distance from both sources will cause constructive interference.
- Path difference: how much farther one wave has travelled than the other
- Constructive or destructive interference depends on path difference
- Destructive interference: (2n+1).lambda/2=(n+1/2)lambda
- You can observe interference with sound waves
- Connect two speakers to the same oscillator (amplifier) and place them in line with each other 2) walk slowly across the room in front of them. 3) you will hear varying volumes of sound. At the point where the sound is loudest, the path difference is a whole wavelength. Where sound is quietest, path difference is an odd number of half wavelengths.
- Loud: no path difference, lambda.
- You will still hear some sound at quietest points due to sound being reflected off walls and around the room.
- Principle of superposition: when two or more waves cross, the resultant displacement = vector sum of individual displacements
- When a crest of one wave meets a slightly smaller trough of another wave, you will get destructive interference that isn't total
- Phase difference=1440 therefore in phase as a multiple of 360
- If a path difference=5.lambda and waves are in phase then interference is constructive.
- Sources must be coherent: Coherence means waves have the same frequency, wavelength and a constant phase difference between them.
- If a path difference=5.lambda and waves are in phase then interference is constructive.
- Phase difference=1440 therefore in phase as a multiple of 360
- When a crest of one wave meets a slightly smaller trough of another wave, you will get destructive interference that isn't total
- Principle of superposition: when two or more waves cross, the resultant displacement = vector sum of individual displacements
- You will still hear some sound at quietest points due to sound being reflected off walls and around the room.
- Loud: no path difference, lambda.
- Connect two speakers to the same oscillator (amplifier) and place them in line with each other 2) walk slowly across the room in front of them. 3) you will hear varying volumes of sound. At the point where the sound is loudest, the path difference is a whole wavelength. Where sound is quietest, path difference is an odd number of half wavelengths.
- Quiet: lambda/2
- You may have difficulty observing interference patterns with two waves from two sources, even if they are coherent because the pattern won't be noticeable unless the amplitudes of the waves are approximately equal.
- Phase difference=360, path difference=lambda/2, interference is constructive
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