Frequencies of the normal mode in standing waves in a string fixed

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Discussion Overview

The discussion revolves around the concepts of phase in wave mechanics, specifically in the context of standing waves in strings fixed at both ends and sound waves in open-ended tubes. Participants seek to clarify the definitions of "in phase" and "out of phase," as well as the nature of standing waves and their relationship to air displacement and pressure variation.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant asks for clarification on the concepts of "in phase" and "out of phase" in relation to waves.
  • Another participant explains that phase difference indicates how much one wave is ahead of another, with specific phase differences leading to constructive or destructive interference.
  • A participant expresses gratitude for the explanation and seeks further understanding of standing waves in open-ended tubes, particularly regarding air displacement and pressure variation.
  • Another participant confirms that sound waves in open-ended tubes are indeed caused by pressure variations in the air.
  • A participant questions the difference between wave patterns resulting from air displacement and those from pressure variation.

Areas of Agreement / Disagreement

The discussion shows a general agreement on the definitions of phase differences and their implications for wave interference. However, there remains uncertainty regarding the relationship between air displacement and pressure variation in sound waves, as one participant seeks further clarification on this aspect.

Contextual Notes

Participants have not fully resolved the differences in understanding the relationship between air displacement and pressure variation in sound waves, indicating a need for further exploration of these concepts.

noobie!
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hi,im a newbie over here,my physics quite poor so i really need help by understanding it,i jz wanted to ask could any1 please explain to me what is in phase,&out of phase?;im totally baffled.:blushingAnd what's frequencies of the normal mode in standing waves in a string fixed in both ends?i hope any1 cud help me with this..tq!:blushing:
 
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If you have two waves, let's assume of the same frequency, you can 'define' a phase difference between them. The phase difference simply tells you how much one wave is 'ahead of' the other wave, and is often given in degrees (0 to 360) or radians (0 to 2pi).

If you look at the following image:
phase.jpg

Clearly, the waves have the same frequency, but one wave is slightly ahead of the other: there is a phase difference between the two.In general, there are a few phase differences of special interest: a phase difference of 0 radians (or 0 degrees) means the waves are exactly "in phase", one is not ahead of the other. A phase difference of pi (or 180 degrees) is often called exactly "out of phase", one wave is exactly half a wavelength ahead of the other wave, which means that the peaks of one wave fall together with the troughs ('dips') of the other wave.

When the two waves are for example sound waves (it is equally valid for all other kind of waves) and when they exist in the same place, then the waves will interfere. A phase difference of 0 will then cause the interference wave to be the sum of both waves. With a phase difference of pi (180 degrees), the peaks and troughs will cancel each other out and the resulting wave is zero everywhere: there is no longer a wave.
 
THANKS a lot man..now i can really understand it completely,thx for ur help,one more thg I am nt clear abt it was the standing waves in an open end due to displacement of air and pressure variation in the air!?i wud appreciate it very much if i understand it...tq!:smile:
 
I assume you are talking about sound waves in an open ended tube? Then yes, they are caused by pressure variation in the air; as are all sound waves...
 
oh you sound waves..but what i dun really understand is the pattern of the waves..why does the waves due to displacement of air differ frm pressure variation in the air?
 

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