TUTORIAL ANSWERS 152-155

 
 


 
Your answer to Q152:  Sorry, your answer is not correct.  Displacement is flat or horizontal at an antinode.

Help: Fundamentals of Sound, Sec. 3-B.

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 152.
 
 


 

Hint for Q152:  When the pressure is normal there is no compression or rarefaction.

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Your answer to Q152:  Congratulations, your answer is correct!

To see the "official" correct answer click HERE.

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Correct answer to Q152:  At a compression or rarefaction the displacement must be zero—the molecule at the center of either does not know which way to go. For example, the molecule at the center of a compression is being crowded by molecules coming towards it from both the left and the right. The displacement is positive (to the right) on the left side of the compression, and negative on the right side of the compression. This is a falling displacement curve and it has a node right at the compression. Similarly the displacement curve around a rarefaction is rising and there is a node at the rarefaction. If the presure is normal, the displacement is maximal, so there is a displacement antinode there and the curve is at a peak and horizontal.

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Your answer to Q153:  Sorry, your answer is not correct.  What wave has the same boundary conditions in a tube closed at both ends as the string tied at both ends?

Help: Fundamentals of Sound, Sec. 3-B.

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 153.
 
 


 

Hint for Q153:  There is a displacement node at the closed end of an air tube.

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Your answer to Q153:  Congratulations, your answer is correct!

    To read the "official" correct answer, click HERE.

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Correct answer to Q153:  The displacement wave has the same kind of boundary conditions (node at a closed end, antinode at an open end) as the string tied or loose at an end. So, if we use the displacement waves, we can use the same boundary conditions as with strings. The correct answer is a).

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Your answer to Q154:  Sorry, your answer is not correct.  Nodes and antinodes are opposite on displacement and pressure waves.

Help: Fundamentals of Sound, Secs. 3-A, 3-C.

Or, would you like a HINT?

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

    Return to Quesiton 154.
 
 


 

Hint for Q154:  Look at the drawings of the molecular distributions and think what the displacements and pressures each should have.

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Your answer to Q154:  Congratulations, your answer is correct!

    To read the "official" correct answer click HERE.

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Correct answer to Q154:  A falling displacement curve corresponds to a compression and a rising curve to a rarefaction. The displacement curve is falling on the left and rising on the right. c) has a compression on the left (peak in the pressure curve) and a rarefaction on the right (trough in the curve) as well as the required nodes on each end. Thus c) is correct.

    Return to Question 154.
 
 


 

Your answer to Q155:  Sorry, your answer is not correct.  Any standing wave is made up of two waves traveling in opposite directions - say the original wave and the reflected wave.

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

Or, would you like a HINT?

You should work out the answer on your own, but if you insist on reading it, click HERE.

Return to Question 155.
 


 

Hint for Q155:  How do the standing wave's wavelength and frequency compare with that of the two waves making it up?

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Your answer to Q155:  Congratulations, your answer is correct!

    To see the "official" correct answer, click HERE.

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Correct answer to Q155:  The standing wave has just the same wavelength and frequency as the two waves making it up (original wave and reflected wave). Thus it has the same period as those two waves. 

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