AAMC official guide C/P discrete question 28

[bluequestions]

Q: "Human speech is generated in the vocal cords as the lungs push air past them. What property of the vocal cords is changed so that the frequency of sound can be altered?"

A. Volume
B. Density
C. Tension
D. Number



Answer: C
"the frequency of the sound produced in vibrating cords and strings (such as vocal cords) of fixed length is proportional to the propagation speed of the sound through the cord. In turn, the propagation speed of a transverse wave (such as the wave in the vocal cords) is directly proportional to the tension applied along the cord."

So in this case, I understand we are treating the sound wave as a transverse wave like a transverse wave on a rope or string. But what I don't get is why is the speed independent of density (as stated by another part of the answer key). Because from TPR books and internet resource, it seems that the propagation speed of a transverse wave in a string is = sqr_root (tension/linear density), shouldn't B and C both affect the propagation speed of sound wave, thus the frequency?

Thanks!

---

Members don't see this ad.

 

[bluequestions]

or is the "density" in answer C referring to "mass/volume", which is not the same thing as "linear density" in the equation.......

 

[aldol16]

I believe they are talking about the physical density of matter making up the vocal cords. That's how I interpreted it. This question I don't think you really need to know much - you can just reason through it. Vocal cords don't really have a physical volume property. Sound does, but your vocal cords aren't characterized by a given volume. You also can't really change the density of your vocal cords - at least not on the time scale we're talking about here. And you can't change the number of your cords either - again, at least not on the time scale we're talking about here.

 

[bluequestions]

That makes sense! Thank you!