# Phase Difference

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#2

**in phase**. But one wave is just 2 wavelengths ahead of the other.

I hope ths is right

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(Original post by

If they are 360 degrees 'apart' or 2 pi radians they are

I hope ths is right

**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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#5

**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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(Original post by

Please post the

The answer to the question on the diagram will be different depending which it is.

**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

(Original post by

Oops sorry, i uploaded another picture, whats the difference between the two?

**Tynos**)Oops sorry, i uploaded another picture, whats the difference between the two?

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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**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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#9

(Original post by

I still dont understand why its 180 out of phase and not 135?

**Tynos**)I still dont understand why its 180 out of phase and not 135?

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.

Your answer refers to a progressive wave travelling left to right.

On a string such as this you have a stationary wave.

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(Original post by

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

Your answer refers to a progressive wave travelling left to right.

On a string such as this you have a stationary wave.

**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.Your answer refers to a progressive wave travelling left to right.

On a string such as this you have a stationary wave.

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?

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#11

(Original post by

Ahh ok for stationary waves:

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

**Tynos**)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?

2(pi)d/lambda

Is this right?

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(Original post by

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

**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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#13

(Original post by

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?

**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?

**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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(Original post by

Well yes,

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.

"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

**Stonebridge**)Well yes,

**in phase**means a phase difference of 0 or 360, 720 degs etcor 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!

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#15

(Original post by

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!

**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!

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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(Original post by

Waves add by superposition so it's not clear cut.

When they are

**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!

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#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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#18

(Original post by

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.

**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.

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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