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Waves Phase difference URGENT HELP PLEASE

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I've been sitting here for a very long time attempting to answer the questions but I cannot. For question 1a) I answered 'the air particles vibrate parallel to the direction of the wave propogation'. For part b) I don't know what is different...
And question 2 is hard! The phase difference between point 0 and A, I put down as 135 degrees but it doesn't seem like it's 135 degrees and I have no clue how to do it...and for part b I put down 3/8 of a wavelength which is 3cm since the question states the whole wavelength is 8cm. But is this correct?
Can someone please help me out? I have done research and I am stuck and I have no answers to these questions! Thank you soooo much...
(edited 7 years ago)
Original post by CounTolstoy
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I've been sitting here for a very long time attempting to answer the questions but I cannot. For question 1a) I answered 'the air particles vibrate parallel to the direction of the wave propogation'. For part b) I don't know what is different...
And question 2 is hard! The phase difference between point 0 and A, I put down as 135 degrees but it doesn't seem like it's 135 degrees and I have no clue how to do it...and for part b I put down 3/8 of a wavelength which is 3cm since the question states the whole wavelength is 8cm. But is this correct?
Can someone please help me out? I have done research and I am stuck and I have no answers to these questions! Thank you soooo much...


section 1 - looks like points A and B are separated by about 1/2 a wavelength... you could confirm with a ruler. since a full wavelength is 360 degrees that would mean they have a phase difference of 360/2 degrees i.e. 180 degrees and what that means is that particles at those points have the same magnitude of displacement at the same instant but in opposite directions (which you can also confirm with a ruler on the first graph)
Since they've both got the same amplitude and frequency you can also say that *at the same instant* they have the same speed (but in opposite directions) and the same magnitude of acceleration (but accelerating in opposite directions)
Original post by Joinedup
section 1 - looks like points A and B are separated by about 1/2 a wavelength... you could confirm with a ruler. since a full wavelength is 360 degrees that would mean they have a phase difference of 360/2 degrees i.e. 180 degrees and what that means is that particles at those points have the same magnitude of displacement at the same instant but in opposite directions (which you can also confirm with a ruler on the first graph)
Since they've both got the same amplitude and frequency you can also say that *at the same instant* they have the same speed (but in opposite directions) and the same magnitude of acceleration (but accelerating in opposite directions)


But how are points 0 and A 180 degrees out of phase as point A is not parallel to point 0 on the axis?
Original post by CounTolstoy
But how are points 0 and A 180 degrees out of phase as point A is not parallel to point 0 on the axis?


well at 180 they should be the same distance from the axis on opposite sides*... & that's what it looks like from here :unsure:

360 is 1 wavelength which is the distance from a peak to the next peak (or trough to trough)
180 is 1/2 a wavelength (or the distance horizontally between a peak and the next trough)
points that are 360 degrees of phase apart are the same distance and direction from the axis **

* this is also the explanation for standing wave nodes & destructive inteference
** this is also the explanation for standing wave antinodes & constructive interference.

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