# Phase Difference

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#1

Are two waves in phase if they are 360 degrees apart only?

Thanks!
0
7 years ago
#2
(Original post by Tynos)

Are two waves in phase if they are 360 degrees apart only?

Thanks!
If they are 360 degrees 'apart' or 2 pi radians they are in phase. But one wave is just 2 wavelengths ahead of the other.
I hope ths is right
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7 years ago
#3
(Original post by Tynos)

Are two waves in phase if they are 360 degrees apart only?

Thanks!
Could be 360*, or any multiplesof 360* e.g.720*
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#4
(Original post by shaw16)
If they are 360 degrees 'apart' or 2 pi radians they are in phase. But one wave is just 2 wavelengths ahead of the other.
I hope ths is right

So in the diagram, it says 180 degrees out of phase, is this roughly because i doesnt look exactly 180 out of phase?

I calculated it to be 135 degrees out of phase.
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7 years ago
#5
(Original post by Tynos)

Are two waves in phase if they are 360 degrees apart only?

Thanks!
Please post the whole question with the background.
Is this a stationary wave or a progressive wave?
The answer to the question on the diagram will be different depending which it is.
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#6
(Original post by Stonebridge)
Please post the whole question with the background.
Is this a stationary wave or a progressive wave?
The answer to the question on the diagram will be different depending which it is.

Oops sorry, i uploaded another picture, whats the difference between the two?
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7 years ago
#7
(Original post by Tynos)
Oops sorry, i uploaded another picture, whats the difference between the two?
The progressive wave is moving so any point that is a whole number of wavelengths is in phase.

From what I remember about standing waves at A-level all the points on the wave between the same two nodes are in phase and the next two nodes are 180* out of phase and then 360* out of phase (in phase again) etc.
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#8
(Original post by Stonebridge)
Please post the whole question with the background.
Is this a stationary wave or a progressive wave?
The answer to the question on the diagram will be different depending which it is.

I still dont understand why its 180 out of phase and not 135?
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7 years ago
#9
(Original post by Tynos)
I still dont understand why its 180 out of phase and not 135?
Because it's a stationary wave.
Look at the wave animation at the bottom of my posts. (Possibly only my 1st post in the thread.)
The blue line is a stationary wave. Look at the black dot at the antinode going up and down.
Now look at the portion of the wave to the left. All points on that are going down up as all points on the one next to it are going up down. Alternate segments of the wire are exactly 180 degs out of phase. All points in that segment are 180 degs out of phase with all points in adjacent segments.
On a string such as this you have a stationary wave.
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#10
(Original post by Stonebridge)
Because it's a stationary wave.
Look at the wave animation at the bottom of my posts. (Possibly only my 1st post in the thread.)
The blue line is a stationary wave. Look at the black dot at the antinode going up and down.
Now look at the portion of the wave to the left. All points on that are going down up as all points on the one next to it are going up down. Alternate segments of the wire are exactly 180 degs out of phase. All points in that segment are 180 degs out of phase with all points in adjacent segments.
On a string such as this you have a stationary wave.
Ahh ok for stationary waves:

If 2 particles seperated by odd number of nodes they are 180 out of phase.

If 2 particles between adjacent nodes then they are 0 phase difference in phase?

Pogressive waves:

2(pi)d/lambda

Is this right?
0
7 years ago
#11
(Original post by Tynos)
Ahh ok for stationary waves:

If 2 particles seperated by odd number of nodes they are 180 out of phase.
yes.

If 2 particles between adjacent nodes then they are 0 phase difference in phase?
Yes, they are in the same segment.

Pogressive waves:

2(pi)d/lambda

Is this right?
Yes if you go from A to B a distance d along a progressive wave of wavelength lambda, that is the phase difference between the vibrations at A and B
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#12
(Original post by Stonebridge)
yes.

Yes, they are in the same segment.

Yes if you go from A to B a distance d along a progressive wave of wavelength lambda, that is the phase difference between the vibrations at A and B

Ok so jsut clear things up, are two particles only in phase if they are 360 / 0 apart? For progressive waves?

All other distances are out of phase?
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7 years ago
#13
(Original post by Tynos)
Ok so jsut clear things up, are two particles only in phase if they are 360 / 0 apart? For progressive waves?

All other distances are out of phase?
Well yes, in phase means a phase difference of 0 or 360, 720 degs etc
or one, two, three etc wavelengths
It requires a whole number of wavelengths or cycles. There's no mystery about this. A wave is just something that repeats for ever and ever. In phase simply means two waves are perfectly in step as they oscillate together. As waves repeat every 360 degs or one whole wavelength, it follows on quite naturally.

"Out of phase" can mean different things. It can just mean "not in phase" so then anything other than the above is out of phase.
It can also mean "antiphase" where the waves are exactly out of phase. This is the case where they are 180 degs or half a wavelength out of phase. That's when you get destructive interference. You just need to keep an eye out for what the question is asking for. It shouldn't cause a problem.
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#14
(Original post by Stonebridge)
Well yes, in phase means a phase difference of 0 or 360, 720 degs etc
or one, two, three etc wavelengths
It requires a whole number of wavelengths or cycles. There's no mystery about this. A wave is just something that repeats for ever and ever. In phase simply means two waves are perfectly in step as they oscillate together. As waves repeat every 360 degs or one whole wavelength, it follows on quite naturally.

"Out of phase" can mean different things. It can just mean "not in phase" so then anything other than the above is out of phase.
It can also mean "antiphase" where the waves are exactly out of phase. This is the case where they are 180 degs or half a wavelength out of phase. That's when you get destructive interference. You just need to keep an eye out for what the question is asking for. It shouldn't cause a problem.

Do the two particles need to be in phase to have constructive interference, because 300 degrees would be classes as out of phase but would still be constructive?

Thanks alot btw!
0
7 years ago
#15
(Original post by Tynos)
Do the two particles need to be in phase to have constructive interference, because 300 degrees would be classes as out of phase but would still be constructive?

Thanks alot btw!
Waves add by superposition so it's not clear cut.
When they are exactly out of phase they can completely cancel and produce nothing at all. This would be complete destructive interference. At all other times there is not complete destruction. That's why the dark and light interference fringes are not like a zebra road crossing which is either black or white, but change slowly from brightest (where the phase diff is exactly 0, 360 etc to darkest where it's 180.) Between the two there are many shades of grey.
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#16
(Original post by Stonebridge)
Waves add by superposition so it's not clear cut.
When they are exactly out of phase they can completely cancel and produce nothing at all. This would be complete destructive interference. At all other times there is not complete destruction. That's why the dark and light interference fringes are not like a zebra road crossing which is either black or white, but change slowly from brightest (where the phase diff is exactly 0, 360 etc to darkest where it's 180.) Between the two there are many shades of grey.

Ahh, thank you very much!
0
6 years ago
#17
(Original post by Stonebridge)
.

Hi, are the points X and Y 90 or 450 degrees out of phase?

I know this is an old thread, didn't want to make a new one for just this.
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6 years ago
#18
(Original post by ubisoft)

Hi, are the points X and Y 90 or 450 degrees out of phase?

I know this is an old thread, didn't want to make a new one for just this.
It doesn't matter.

They are equivalent.

If you wanted to be really pedantic you would have to say 450. But given that after 360 degs the cycle repeats, then what is the difference?
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5 days ago
#19
(Original post by Stonebridge)
yes.

Yes, they are in the same segment.

Yes if you go from A to B a distance d along a progressive wave of wavelength lambda, that is the phase difference between the vibrations at A and B
wait sorry if the particles are btwn adjacent nodes why is the phase difference 0??

sorry ik this is an old thread but no one is responding to my new threadsss
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