EK Physics Exam #138

[IlyaR]

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I narrowed the question to B and C, and the logic behind B makes sense to me (it's the correct answer), but I don't understand why C isn't correct. Wouldn't less liquid in the glass cause smaller harmonic wavelengths, thus larger frequencies?

 

[milski]

I narrowed the question to B and C, and the logic behind B makes sense to me (it's the correct answer), but I don't understand why C isn't correct. Wouldn't less liquid in the glass cause smaller harmonic wavelengths, thus larger frequencies?

C talks about less air and more liquid in glass A, which is the opposite of what you describe? 😕

 

[IlyaR]

Sorry, I meant more liquid*, thus less air would be in the glass

 

[milski]

More liquid -> more inertia -> lower frequency/longer wavelength.

It's the inverse argument of B.

The whole argument hinges on more mass resulting in lower resonant frequency, the answers are just rephrasing that or the opposite statement in different ways.

 

[IlyaR]

RIght, but in a vessel in which one end is open, wouldn't the wavelength be longer in the one that has a larger L? (in this case, glass B, which has less liquid in it, thus a longer L)

 

[milski]

RIght, but in a vessel in which one end is open, wouldn't the wavelength be longer in the one that has a larger L? (in this case, glass B, which has less liquid in it, thus a longer L)

That would be true if it was the air vibrating. In the question they tell us that it is actually the wine and the glass vibrating, thus anything that we know about pipes is not directly applicable. Based on that, they make their conclusions about the resonant frequency considering only the amount of mass resonating.

Honestly, I don't feel too comfortable with the answer and think that they have somewhat oversimplified the question but a precise treatment of what the resonant frequency is going to be is rather complicated.

 

[IlyaR]

That makes a lot of sense, thank you!