TUTORIAL ANSWERS 520-545

 
 
 

Your Answer to Q520.  Sorry, your answer is not correct. Don't forget to incude the use of the reference level Imin.

Help: Fundamentals of Sound, Sec. 11-F.

Or would you like a HINT?

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

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Hint for Question 520:  To convert to dB, you divide I by the reference level, 10-12W/m2 and then find the log of that number. The dB level is 10 times that log.
 
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Your Answer to Q520. Congratulations, your answer is correct.

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Correct Answer to Question 520:  I/Imin = 5x10-8/10-12 = 5x104 = 104.7. The exponent 4.7 is the log of the previous number. The decibel level is then 47 dB, that is answer c).

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Your Answer to Q530.  Sorry, your answer is not correct.  The 89 is related to the logarithm of the number you want. So you have to take an antilog.

Help: Fundamentals of Sound, Sec. 11-H.

Or would you like a HINT?

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

Return to Question 530.

 

 

Hint for Question 530: To convert to intensity, you divide the decibel level by 10 to convert to Bels. This number is the power of ten (log) of the ratio of intensities I/Imin. Find its antilog and multiply by the reference level Imin = 10-12W/m2

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Your Answer to Q530. Congratulations, your answer is correct.

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Correct Answer to Question 530:  89 dB = 8.9 Bels. Thus I/Imin = 108.9 = 100.9 x 108 = 7.9 x 108. In the last step we used the log table to find the antilog of 0.9. We multiply the result by the reference level to get the intensity: I = 7.9 x 108 x 10-12 W/m2 = 7.9 x 10-4 W/m2, which is answer b).

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Your Answer to Q540.  Sorry, your answer is not correct.  Multiply the intensity by 5 and convert normally to dB.

Help: Fundamentals of Sound, Sec. 11-K.

Or would you like a HINT?

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

Return to Question 540.

 

 

Hint for Question 540:  Multiply the intensity by 5 and convert normally to dB. To convert to dB, you divide the total intensity by the reference level, 10-12W/m2 and then find the log of that number. The dB level is 10 times that log.
 
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Your Answer to Q540. Congratulations, your answer is correct.

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

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Correct Answer to Question 540:  5 I/Imin = 5x10-2/10-12 = 5x1010 = 1010.7. The decibel level is then 107 dB, that is answer c).

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Your Answer to Q545.  Sorry, your answer is not correct.  The 40 dB sound is quite a bit more intense than the 30 dB sound. Note that you cannot just add the dB levels.

Help: Fundamentals of Sound, Sec. 11-K.

Or would you like a HINT?

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

Return to Question 545.

 

 

Hint for Question 545:  The 40 dB sound is quite a bit more intense than the 30 dB sound. Thus you know your answer is pretty close to 40 dB without doing any math. But to determine which of the remaining possible answers it is you may need to do the math. Incidentally you know the answer cannot be 44 dB because doubling the sound intensity raises the level by only 3 dB so that 40 dB + 40 dB is a total intensity of only 43 dB. So 44 dB is too much in this problem.
 
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Your Answer to Q545. Congratulations, your answer is correct.

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Correct Answer to Question 545:  The ratio of total intensity to reference level is (I1 + I2 )/Imin = 104.0 + 103.0 = 1 x 104.0 + 0.1 x 104.0 = 1.1 x 104.0 = 100.04 x 104.0 = 104.04. The exact answer is then 40.4 dB and c) is closest.

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