WAVES and AAMC 3

[crazy person]

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Hi all ! I'm having trouble looking at the different waves on a graph. On AAMC 3, for question 22, aamc says that the first harmonic is the longest wavelength, but shouldn't that be a second harmonic according to the picture ?

I have read TBR and Nova and Tpr for this chapter, and they all show the first harmonic (fundamental) with 1/2 of a wavelenth and the second harmonic exactly the same as the wave that the AAMC calls the first harmonic.


THANKS GUYS !!!

 

[benjaminl1nus]

ok, for a pipe with ends open, frequency = nv/2L

where n = 1, 2, 3...etc. 1, 2, 3 correspond to 1st, 2nd, 3rd harmonics, respectively.

notice that as n gets larger, frequency gets larger. as frequency gets larger, wavelength gets proportionally smaller. make sense?

The 2nd harmonic should not be the exact same wave as the 1st harmonic. it should have twice the frequency and therefore half the wavelength.

 

[crazy person]

I got that. But what I'm saying is that the picture shows the first harmonic as a full wavelength and according to TPR, it says that a full wavelength is a second harmonic, while a first harmonic is 1/2 of a wavelength. So I'm confused in term of why the AAMC is calling that full wavelength picture the first harmonic when its supposed to be a second harmonic for open pipes. It says the same thing from TBR and Nova. That's where I'm getting confused with the drawings.

 

[crazy person]

Do you know what I mean ??

 

[benjaminl1nus]

I'm not sure if I do. I know how this wave stuff can be confusing, though.

Just know that the passage mentions 3 consecutive harmonics. you should infer that the 1st harmonic will therefore be the one with the lowest frequency and the longest wave length.

the picture shows the first harmonic as a full wavelength

No, the picture shows one full wavelength of the first harmonic. The first harmonic is not limited to a half wavelength (this is maybe where you are getting confused?)

does this make sense? I feel like I don't understand where exactly you're confused...

 

[crazy person]

Just know that the passage mentions 3 consecutive harmonics. you should infer that the 1st harmonic will therefore be the one with the lowest frequency and the longest wave length.

I was missing that little detail ( key word: 3 consecutive harmonics ) but yes you are right, I should immediately think 1st harmonic think lowest frequency and the longest wave length . I better start making flashcards !



No, the picture shows one full wavelength of the first harmonic. The first harmonic is not limited to a half wavelength (this is maybe where you are getting confused?)

Yes, that's exaxtly where I was getting confused ! Ohhhhh..... k . I see it now. For some reason, I always thought that a half wavelength will always be the first harmonic.

Ok. now I understand it. Thanks ! 🙂

 

[Liza21]

What is AAMC.

 

[dudewheresmymd]

This should be in the AAMC 3 thread as to not spoil it for people who have not taken the test.

 

[SN2ed]

Thread closed. These types of questions belong in the appropriate AAMC Q&A thread.