Standing wave, phase and antiphase

[maxelcat]

Homework Statement

The diagram shows a stationary wave on a string at one instant in time. box
P, Q and R are three points on the string.

Relevant Equations

none that I think are needed...

I think I understand that points P and R are pi radians out of phase - reaching their max/min at the same time.
But are P and Q in anti phase?

What is antiphase exactly - is it when they are 180deg out of phase - or is it when they are anything other than totally in phase? I seem to find conflicting answers

Thanks

 

[Steve4Physics]

View attachment 320750I think I understand that points P and R are pi radians out of phase - reaching their max/min at the same time.

Agreed.

But are P and Q in anti phase?

What is antiphase exactly - is it when they are 180deg out of phase - or is it when they are anything other than totally in phase? I seem to find conflicting answers

Watch the animation carefully:
https://www.cyberphysics.co.uk/graphics/animations/standing-wave.gif

Antiphase is a phase difference which is an exact odd-integer multiple of π (180º), i.e. π rad, 3π rad, 5π rad, etc.

Edit. The term 'out of phase' is often used to mean any phase difference different to 'in phase'. It is not the same as 'anti phase'.

So do you now think P and Q are in phase, antiphase, or neither?

 

[nasu]

Your homework statement is incomplete. There is no question there.

 

[Gordianus]

My eyes aren't what they used to be but I think the phase difference between P and R isn't 180 degrees. I see R is at the "bottom" of the wave whereas P isn't at the "top"

 

[Steve4Physics]

My eyes aren't what they used to be but I think the phase difference between P and R isn't 180 degrees. I see R is at the "bottom" of the wave whereas P isn't at the "top"

Remember that the question is about a stationary (standing) wave, not a progressive wave. Watching the animation in Post #2 should clarify the issue.

Edit: P and R are 180º out of phase, but with different amplitudes.

 

[maxelcat]

Your homework statement is incomplete. There is no question there.

actually it is there because the question is to identify which is antiphase

 

[maxelcat]

Agreed.Watch the animation carefully:
https://www.cyberphysics.co.uk/graphics/animations/standing-wave.gif

Antiphase is a phase difference which is an exact odd-integer multiple of π (180º), i.e. π rad, 3π rad, 5π rad, etc.

Edit. The term 'out of phase' is often used to mean any phase difference different to 'in phase'. It is not the same as 'anti phase'.

So do you now think P and Q are in phase, antiphase, or neither?

no I think P and Q are in phase (both reaching their max at the same time - thanks for the explanation - very helpful

 

[nasu]

actually it is there because the question is to identify which is antiphase

There is no question in the OP, under "Homework statement". You start by saying what you think without saying what is the actual question and how is that relevant.