# Stationary waves

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#1
Are the transmitted and the reflected waves always in phase when they are at antinodes; and are always in antiphase when at nodes? Or is it the other way round? I don't understand why though. I don't get how standing waves can be in phase and in antiphase.
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4 years ago
#2
A stationary wave is a wave such that two waves with the same amplitude and frequency travelling in opposite directions meet and essentially counteract by kinda cancelling the other about.

By this I mean the net displacement away from the imaginary horizontal line through the centre of the resulting wave forme is 0 at all parts of the wave.
This would mean that if an antinode has a displacement (amplitude) of +3 away from the horizontal line then that would need to be counteracted by a wave with a displacement of -3 as you always add the displacements of the two waves meeting. This will result in an overall horizontal line on top of your existing imaginary line.

A node is a point in a wave where your amplitude is 0, so where it crosses your horizontal line.

An antinode is a point on a wave where the amplitude is at it's maximum.

Node:
'At these points, the two waves add with opposite phase and cancel each other out. They occur at intervals of half a wavelength (λ/2). Midway between each pair of nodes are locations where the amplitude is maximum. These are called the antinodes.'
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#3
(Original post by S.H.Rahman)
A stationary wave is a wave such that two waves with the same amplitude and frequency travelling in opposite directions meet and essentially counteract by kinda cancelling the other about.

By this I mean the net displacement away from the imaginary horizontal line through the centre of the resulting wave forme is 0 at all parts of the wave.
This would mean that if an antinode has a displacement (amplitude) of +3 away from the horizontal line then that would need to be counteracted by a wave with a displacement of -3 as you always add the displacements of the two waves meeting. This will result in an overall horizontal line on top of your existing imaginary line.

A node is a point in a wave where your amplitude is 0, so where it crosses your horizontal line.

An antinode is a point on a wave where the amplitude is at it's maximum.

Node:
'At these points, the two waves add with opposite phase and cancel each other out. They occur at intervals of half a wavelength (λ/2). Midway between each pair of nodes are locations where the amplitude is maximum. These are called the antinodes.'
So the transmitted and the reflected waves must be in phase at antinodes, and in antiphase at nodes?
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4 years ago
#4
(Original post by Kaelyn327)
So the transmitted and the reflected waves must be in phase at antinodes, and in antiphase at nodes?
Sorry if I've confused you.

They are at antiphase or completely out of phase at nodes but are in phase at antinodes.

'The two waves are not "in antiphase" (constantly, that is) and they do cancel each other out. They cancel out at the nodes (antiphase) but reinforce at the antinodes where they are in phase. You do always get a standing wave in this case if the waves have the same frequency (and thus same wavelength).'
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#5
(Original post by S.H.Rahman)
Sorry if I've confused you.

They are at antiphase or completely out of phase at nodes but are in phase at antinodes.

'The two waves are not "in antiphase" (constantly, that is) and they do cancel each other out. They cancel out at the nodes (antiphase) but reinforce at the antinodes where they are in phase. You do always get a standing wave in this case if the waves have the same frequency (and thus same wavelength).'
Nah, it's fine. So you know most stationary waves diagrams in textbooks, they have one solid and one dotted line to show the waves and nodes. Is it just a visual image of both incoming and reflected wave combined together? So it's not showing how the transmitted and reflected waves should look like separately?
So if the two waves are in phase, they interference constructively, and thus results in bigger crest and bigger trough, and so antinodes are formed in the combined visual image. (?)
And if the two waves are in antiphase, they interference destructively, which means they cancel out each other and results in nodes in the combined image. (?)
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4 years ago
#6
(Original post by Kaelyn327)
Nah, it's fine. So you know most stationary waves diagrams in textbooks, they have one solid and one dotted line to show the waves and nodes. Is it just a visual image of both incoming and reflected wave combined together? So it's not showing how the transmitted and reflected waves should look like separately?
So if the two waves are in phase, they interference constructively, and thus results in bigger crest and bigger trough, and so antinodes are formed in the combined visual image. (?)
And if the two waves are in antiphase, they interference destructively, which means they cancel out each other and results in nodes in the combined image. (?)
Could I see this picture?
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#7
(Original post by S.H.Rahman)
Could I see this picture?
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4 years ago
#8
I've confused myself now argh D: Someone else plz come help?! lol
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4 years ago
#9
http://www.walter-fendt.de/html5/phe...lection_en.htm

This website shows how standing waves work well imo
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4 years ago
#10
Basically as both waves are traveling in opposite directions there can be a moment where they are completly in phase and a moment where they are completly out of phase
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