TUTORIAL ANSWERS 110-125

 

 

Your answer to Q110:  Sorry, your answer is not correct.  The term "dynamic parameters" refers to things like tension of a string, for example, or the force of gravity on water, when there are waves on those media. An "inertial parameter" is the density or mass of the medium.

Help: Fundamentals of Sound, Secs. 1-G, 1-H.

Or, would you like a HINT?

You should really try to work out the answer on your own, but if you insist on reading it, the correct answer is HERE.
 
Return to Question 110.

Hint for Q110:  How would you change the wave velocity of a wave on a string? How would you go about changing the frequency of a sinusoidal wave?

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Your answer to Q110:  Congratulations, your answer is correct!

If you like, you can compare your answer to the "official" correct answer.

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Correct answer to Q110:   The wave velocity depends on the properties of the medium such as the tension of a string or its density (the dynamical and inertial properties mentioned). However a wave of any frequency can be placed on the string just by jiggling your hand up and down more or less often. When you change the frequency you change the wavelength such that the formula in a) holds; the higher the frequency the smaller the wave length — with the wave velocity staying constant unless you change the medium. Thus g) is correct.

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Your answer to Q115:  Sorry, your answer is not correct. What are the differences between standing waves and traveling waves?

Help: Fundamentals of Sound, Sec. 2-C.

Or, would you like a HINT?

You should really try to work out the answer on your own, but if you insist on reading it, the correct answer is here.

Return to Question 115.
 

Hint for Q115:  One makes a standing wave by enforcing boundaries on the medium so that there is reflection at the boundaries. For a string tied at both ends, the ends are fixed. What condition does that put on the wavelength?

    Return to Question 115.

 

Your answer to Q115:  Congratulations, your answer is correct!

If you like, you can compare your answer to the "official" correct answer.
 
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Correct answer to Q115:  When you tie the ends of a string down the wavelength must be such that there are zeros (nodes) of the wave at the ends. This means that we cannot have just any wavelength; the wavelength must be adjusted to fit into the space properly. Thus only certain wavelengths, and hence frequencies, are allowed and b) becomes true. As in Question 110 c) and d) are also true. Thus the correct answer is f).

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Your answer to Q120:  If you got 6ft you are correct;  if not, you have made an error. You measure wavelength of a standing wave just like any other wave. Note that the wave velocity information given is irrelevant. Try again.

Help: Fundamentals of Sound, Sec. 2-C.

You should really try to work out the answer on your own, but if you insist on reading it, the correct answer is HERE.

Return to Question 120.
 


 


 

Correct answer to Q120:  The wavelength is the peak-to-peak distance, but can also be measured in the following way: start at the left end, a node, move past the first crest to the next node (1/3 of the way along), move past the trough to the third node (2/3 of the length). You have moved a wavelength and it is 2/3 of the entire string length of 2/3 of 9 = 6ft

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Your answer to Q125:  Sorry, your answer is not correct.  Recall that the fundamental = first harmonic; first overtone = 2nd harmonic; second overtone = 3rd harmonic, etc.
 
Help: Fundamentals of Sound, Sec. 2-C.

Or, would you like a HINT?

You should really try to work out the answer on your own, but if you insist on reading it, the correct answer is here.

Return to Question 125.

Hint for Q125:  You can determine the harmonic or overtone by counting the number of antinodes. The fundamental has one antinode.
 
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Your answer to Q125:  Congratulations, your answer is correct!

If you like, you can compare your answer to the "official" correct answer.

Return to Question 125.

Correct answer to Q125:  This is the 3rd harmonic or the 2nd overtone. The fundamental (or 1st harmonic) has just one antinode fitting between the two walls (and two nodes—at the ends). The first overtone (2nd harmonic) has two antinodes (or three nodes); and the second overtone (3rd harmonic) has three antinodes (four nodes). This problem's figure shows three antinodes and so g) is the correct answer.

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