Difficult BR problem on speed of sound in pipes.

[hellocubed]

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I'm working on this problem and went through the answer and realized something at the end.
The problem seems to be unsolvable.

The reason is because they tell you to use the equation f=n(v/2L), but they fail to tell you anything about the frequency between the two pipes. If the frequency is not constant, I don't believe that you can relate the n and L of two completely different systems?

 

[chiddler]

that's the thing; frequency always depends on the source and never changes even when the wave crosses mediums.

 

[hellocubed]

that's the thing; frequency always depends on the source and never changes even when the wave crosses mediums.

Not quite sure what you mean... the wave is not crossing any medium.
The problem actually has nothing to do with mediums

 

[chiddler]

Not quite sure what you mean... the wave is not crossing any medium.
The problem actually has nothing to do with mediums

i was emphasizing that f doesn't change easily, even when crossing mediums.

 

[ipodtouch]

i was emphasizing that f doesn't change easily, even when crossing mediums.

Hmm, are you implying that there is a frequency of air that enters the pipes? and hence the frequency of the two pipes should be the same?

The OP seems to have a point. There is no initial frequency until it is created via the instrument through air pressure and reflection through the tubes. Two different instruments, two different frequencies.


Could you perhaps elaborate on your point?

 

[chiddler]

Hmm, are you implying that there is a frequency of air that enters the pipes? and hence the frequency of the two pipes should be the same?

The OP seems to have a point. There is no initial frequency until it is created via the instrument through air pressure and reflection through the tubes. Two different instruments, two different frequencies.


Could you perhaps elaborate on your point?

I mean in general, frequency of any given wave depends on the source. Therefore, OP's concern that frequency is not constant is unwarranted because it is in fact constant.

Do you mean that the concern is that the frequency of sound used in each pipe experiment may be different?

I don't know it never occurred to me because it seems very unlikely that a systematic experiment would do that. Plus the answers do not suggest this possibility either. I think this is what was being referred to. I misunderstood initially, sorry.

 

[hellocubed]

I mean in general, frequency of any given wave depends on the source. Therefore, OP's concern that frequency is not constant is unwarranted because it is in fact constant.

Do you mean that the concern is that the frequency of sound used in each pipe experiment may be different?

I don't know it never occurred to me because it seems very unlikely that a systematic experiment would do that. Plus the answers do not suggest this possibility either. I think this is what was being referred to. I misunderstood initially, sorry.

No prob.

If this problem involved One source, then it would be no problem.


But the illustration is this:
2 different instruments have air blown through them, and display different natural frequencies when blown into them.

The concern is that the source is two different instruments. Hence.... 2 different sources. 2 different frequencies....

 

[EnginrTheFuture]

I agree, being able to answer this question unfortunately depends on you assuming that the frequency of the waves being made in both pipes are the same.

I agree with the OP that they don't give the frequency and that is confusing BUT the equation

n = f 2L / v

indicates that the slope of this graph is the constant f/v... no they don't give you the f of the wave in either pipe BUT the key here is which is the best answer? If you look for the right answer based on what you know because you're a inquisitive smart future doctor, you'll be left scratching your head. But there is clearly an answer that could explain this better than the other answers and it is B. Totally got frustrated over this one at first too. Then I played dumb and got it right.

 

[SaintJude]

When they said that both pipes are "telescoping pipes" (no clue what those are), I just assumed that they same type of instruments with similar materials and structure.

And they are measuring the values of resonant frequencies, which, as I understand it, is an entirely separate issue from measuring frequency of sound.