Contradiction in Phase of reflected sound

[Vivek98phyboy]

Homework Statement

While studying the fundamentals of sound waves in organ pipe, I noted that the fact about phase of reflected waves is contradicting while referring multiple sources

Relevant Equations

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While studying the fundamentals of sound waves in organ pipe, I noted that the fact about phase of reflected waves is contradicting while referring multiple sources

This book of mine describes the reflection from a rigid surface/closed end to be in phase

Whereas this one describes the reflection from a closed end to be 180° out of phase

Yet, both the books says that, "compression returns as compression and rarefaction returns as rerefaction, from a hard surface" and I found it to be true in all the sources i referred. But this phase change described by them is completely contradicting with each other. I found the same issue while referring some online portals on this topic.

Why are these books contradicting each other?

Initially I thought that one of them might be discussing about pressure wave and another one about displacement wave, as they have a 90° phase difference at any point of time. But even in such case, a phase of difference of 180° shouldn't be produced, right?

 

[haruspex]

one of them might be discussing about pressure wave and another one about displacement wave, as they have a 90° phase difference at any point of time.

Quite so.
The pressure and displacement functions can be a quarter cycle out of phase in opposite directions, so the two waves can be in phase for pressure but half a cycle out of phase for displacement.