nodes/ antinodes

[Jiller1994]

TPR FL practice test question (chem section) gives a question asking what happens at the end of an open air column in an instrument.

Without any background knowledge from the passage, I assume that closed ends have nodes because air is not moving at that point and antinodes at open ends because the wave can expand at that point.

Apparently this is backwards and upon rereading the appropriate part of the passage I see that they do mention this. Any input on whether I'm totally wrong or maybe there are different ways that waves behave?

Thanks in advance

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[Cawolf]

A picture is very illustrative if you do not know the formulas.

See how a closed column (or a string tied to a pole) has the wavelength go to zero at the fixed point (node).

The open column has a node at half the length of the tube (first harmonic or fundamental frequency) and an anti-node at the ends.

 

[hypericum]

No, you are right that nodes are at closed ends and antinodes are at open ends. I'm confused about what is "backwards" about that.

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/funhar.html#c3

 

[NextStepTutor_3]

Yes, nothing is backwards from the way you explained it. You were right originally - nodes fall at the closed ends of pipes, while antinodes are found at open ends. Is it possible that you misread the passage?

 

[pjericho]

When considering nodes and antinodes of waves in a tube, we have two types of waves: either displacement or pressure.
Displacement will be maximum (antinode) at the open end and a minimum at the closed end. Make sense if you think about it.
Pressure otherwise, will be maximum (antinode) at the closed end and minimum, or node at the open end (equal atmospheric P).
Here is an image for illustration. Hope it help! (source: hyperphysics.gsu.edu)