# Phase difference

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#1
I don't understand the second part of the question regarding X and Z:

I understand why X and Y have a phase relationship of being in 'antiphase', but I don't understand why X and Z have a phase relationship of being 'in phase' according to the mark scheme. The phase difference between the two is 315o w/hich is not a whole number of wavelengths... could someone please clear this up for me

Thanks!
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6 years ago
#2
(Original post by park1996)
I don't understand the second part of the question regarding X and Z:

I understand why X and Y have a phase relationship of being in 'antiphase', but I don't understand why X and Z have a phase relationship of being 'in phase' according to the mark scheme. The phase difference between the two is 315o w/hich is not a whole number of wavelengths... could someone please clear this up for me

Thanks!
This is a stationary wave, so the phase difference equation d = (2 x pi x lambda)/lambda is invalid.

The equation you should be using is phase difference d = m x pi, where m is the number of nodes between the two points. There are 2 nodes between X and Z so the phase difference = 2pi radians, or 360 degrees 0
6 years ago
#3
(Original post by park1996)
I don't understand the second part of the question regarding X and Z:

I understand why X and Y have a phase relationship of being in 'antiphase', but I don't understand why X and Z have a phase relationship of being 'in phase' according to the mark scheme. The phase difference between the two is 315o w/hich is not a whole number of wavelengths... could someone please clear this up for me

Thanks!

On a stationary wave, all points between any two nodes are in phase. They all move up and down together. If you then move along to the next section of string, again all the points are going up and down together, but they are in antiphase to the adjacent group.

If you can see the animation at the bottom of my post you will see a stationary wave. (the 3rd, blue wave.) Notice all the points going up and down together between two nodes, and doing the same but out of phase in the next space between the next two nodes.
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#4
(Original post by jf1994)
This is a stationary wave, so the phase difference equation d = (2 x pi x lambda)/lambda is invalid.

The equation you should be using is phase difference d = m x pi, where m is the number of nodes between the two points. There are 2 nodes between X and Z so the phase difference = 2pi radians, or 360 degrees Ahh right thanks I get it!

So, if there are a even number of nodes after the point X, a point in the antinode would be in phase, but a point located after an odd number of nodes after the point X, the point would be in antiphase?
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#5
(Original post by Stonebridge)
On a stationary wave, all points between any two nodes are in phase. They all move up and down together. If you then move along to the next section of string, again all the points are going up and down together, but they are in antiphase to the adjacent group.

If you can see the animation at the bottom of my post you will see a stationary wave. (the 3rd, blue wave.) Notice all the points going up and down together between two nodes, and doing the same but out of phase in the next space between the next two nodes.

Thank you.

So for the point X and Z, because the point Z is 2 group ahead, it's in phase. So am I right in thinking that the group adjacent to the one Z is in (on the right) would be in antiphase?
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6 years ago
#6
(Original post by park1996)
Thank you.

So for the point X and Z, because the point Z is 2 group ahead, it's in phase. So am I right in thinking that the group adjacent to the one Z is in (on the right) would be in antiphase?

Yes that's exactly right.
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#7
(Original post by Stonebridge)
Yes that's exactly right.
Also, is the phase difference value between X and Z zero if the wave is a stationary wave, but if its a progressive wave would the phase difference be 315 degrees?
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6 years ago
#8
(Original post by park1996)
Also, is the phase difference value between X and Z zero if the wave is a stationary wave, but if its a progressive wave would the phase difference be 315 degrees?

Yes. It's a guess that the actual value is 315 but it looks about right. It doesn't say in the question but it looks like X is about a quarter of a cycle past the crest. That would be 45 degs and put it 360 - 45 out of phase with Z on a progressive wave.
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#9
(Original post by Stonebridge)
Yes. It's a guess that the actual value is 315 but it looks about right. It doesn't say in the question but it looks like X is about a quarter of a cycle past the crest. That would be 45 degs and put it 360 - 45 out of phase with Z on a progressive wave.
So essentially the point Z, if the wave was stationary would be in phase, and if the wave was progressive then the point would be antiphase right?
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6 years ago
#10
(Original post by park1996)
So essentially the point Z, if the wave was stationary would be in phase, and if the wave was progressive then the point would be antiphase right?
Yes if stationary the points would be in phase.
No, if progressive they would be, as you have guessed, 315 degs out of phase. That is not what is called anti phase. Anti phase is 180 degs out of phase.
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#11
(Original post by Stonebridge)
Yes if stationary the points would be in phase.
No, if progressive they would be, as you have guessed, 315 degs out of phase. That is not what is called anti phase. Anti phase is 180 degs out of phase.

Ah right. Thank you so much!
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