a level physics-waves-phase difference

All particles vibrate with the same phase between adjacent nodes or if separated by an even number of nodes. If separated by an odd no of nodes the phase difference = 180° or π radians
I don't really get this
and when do you use the equation 2 x pie x d / wavelength

Original post by student144

All particles vibrate with the same phase between adjacent nodes or if separated by an even number of nodes. If separated by an odd no of nodes the phase difference = 180° or π radians
I don't really get this
and when do you use the equation 2 x pie x d / wavelength

First of all, you need to realize that you are comparing 2 different types of waves.
The phase differences in a progressive wave and standing wave are different.

\dfrac{2 \times \pi \times d }{\lambda}

is meant for progressive wave NOT standing wave.

Reply 2

Physics Enemy

19

Original post by student144

...

As a particle vibrates its phase changes, as it moves up/down through its cycle. 0 to A is pi/2, down to 0 is pi, down to -A is 3pi/2, up to 0 is 2pi - a full cycle. This happens in both stationary and propagating waves.

Stationary waves: all particles between nodes 1&2 vibrate in-phase. So do those in 2-3, but anti-phase to 1-2. Think of 1-2 as a loop above zero line, 2-3 below. So node 2 separates them. Particles in 3-4 in-phase with 1-2 ('above' loops), separated by 2 nodes (2&3). So an odd separation = anti-phase, even = in-phase.

As Eimmanuel said, we use 2dpi/lambda for phase difference between 2 points on a propagating wave. For stationary waves, find the no. nodes between 2 particles, the phase difference is 0 or pi (only).

(edited 4 years ago)

Original post by Physics Enemy

As a particle vibrates its phase changes, as it moves up/down through its cycle. 0 to A is pi/2, down to 0 is pi, down to -A is 3pi/2, up to 0 is 2pi - a full cycle. This happens in both stationary and propagating waves. …

I don’t follow what you are describing or explaining in this paragraph. As far as I know, the phase of a wave is not related to the amplitude or displacement of the particle along with the wave.

When you say “This happens in both stationary and propagating waves.”, I"m also not sure what are you referring to. For stationary or standing wave, the particles along the waves have different amplitudes which are different from the progressive waves.

Reply 4

Physics Enemy

19

Original post by Eimmanuel

I don’t follow what you are describing or explaining in this paragraph. As far as I know, the phase of a wave is not related to the amplitude or displacement of the particle along with the wave.

When you say “This happens in both stationary and propagating waves.”, I"m also not sure what are you referring to. For stationary or standing wave, the particles along the waves have different amplitudes which are different from the progressive waves.

Transverse wave, standing or progressive. As a wave completes 1 cycle, a particle does 1 cycle of vertical oscillation. For 2 particles of different amplitudes in standing waves, it occurs in/anti phase. Particles of progressive waves have amplitude A, travel 4A per wave cycle, their phase difference calc as above.

(edited 4 years ago)

Original post by Physics Enemy

Transverse wave, standing or progressive. As a wave completes 1 cycle, a particle does 1 cycle of vertical oscillation. For 2 particles of different amplitudes in standing waves, it occurs in/anti phase. Particles of progressive waves have amplitude A, travel 4A per wave cycle, their phase difference calc as above.

It seems that you have been changing or editing your reply.
IMO, this writing is very from different from the paragraph that I quoted previously.

a level physics-waves-phase difference

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