# Phase difference in progressive waves

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#1
Could somebody please explain to me phase difference in a standing wave? Apparently at the nodes the phase difference is always 180 but i don't understand that, as is phase difference talking about individual points on the two standing waves or the standing waves as a whole? Surely the two waves can't always be 180 out of phase as when the stationary waves superimpose and the antinode is at a maximum they are in phase? I just can't visualise the phase difference at all? Thanks
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3 years ago
#2
(Original post by mayjb)
Could somebody please explain to me phase difference in a standing wave? Apparently at the nodes the phase difference is always 180 but i don't understand that, as is phase difference talking about individual points on the two standing waves or the standing waves as a whole? Surely the two waves can't always be 180 out of phase as when the stationary waves superimpose and the antinode is at a maximum they are in phase? I just can't visualise the phase difference at all? Thanks
The wave propagates along the string and returns back in the opposite direction.

Where the two opposing direction waves meet, the waves cancel when they are 180 out if phase. i,e, there will be no apparent motion.

Where the waves are in phase, the wave appears as double the maximum amplitude of the two individual waves.

The key thing is to recognise that a continuous sinusoidal wave reflected back on itself, will create constructive and destructive interference which makes the wave appear as if it was standing in one position but in reality it's the reflection travelling in the opposite direction creating nodes and anti-nodes.

Have a look at thus youtube video from 9'30" which shows the principle very well. The whole video is good revision by the way.

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#3
(Original post by uberteknik)
The wave propagates along the string and returns back in the opposite direction.

Where the two opposing direction waves meet, the waves cancel when they are 180 out if phase. i,e, there will be no apparent motion.

Where the waves are in phase, the wave appears as double the maximum amplitude of the two individual waves.

The key thing is to recognise that a continuous sinusoidal wave reflected back on itself, will create constructive and destructive interference which makes the wave appear as if it was standing in one position but in reality it's the reflection travelling in the opposite direction creating nodes and anti-nodes.

Have a look at thus youtube video from 9'30" which shows the principle very well. The whole video is good revision by the way.

Thanks for the help ill check it out!
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