You dont have javascript enabled! Please enable it! Giancoli: MCQ in Sound | ECE Board Exam

# Giancoli: MCQ in Sound | ECE Board Exam

Begin and Good luck!
1. When a sound wave passes from air into water, what properties of the wave will change?
• A)      the frequency f
• B)     the wavelength ฮป
• C)      the speed of the wave
• D)      both f and ฮป
• E)      both vwave and ฮป

2. We just determined that the wavelength of the sound wave will change when it passes from air into water.   How will the wavelength change?
• A)      wavelength will increase
• B)      wavelength will not change
• C)      wavelength will decrease
3. Do sound waves travel faster in water or in ice?
• A)      water
• B)      ice
• C)      same speed in both
• D)      sound can only travel in a gas
4. Do you expect an echo to return to you more quickly or less quickly on a hot day, as compared to a cold day?
• A)      more quickly on a hot day
• B)      equal times on both days
• C)      more quickly on a cold day
5. If you fill your lungs with helium and then try talking, you sound like Donald Duck.   What conclusion can you reach about the speed of sound in helium?
• A)      speed of sound is less in helium
• B)      speed of sound is the same in helium
• C)      speed of sound is greater in helium
• D)      this effect has nothing to do with the  speed in helium
6. You drop a rock into a well, and you hear the splash 1.5 s later.  If the depth of the well were doubled, how long after you drop the rock would you hear the splash in this case?
• A)      more than 3 s later
• B)      3 s later
• C)      between 1.5 s and 3 s later
• D)      1.5 s later
• E)      less than 1.5 s later
7. You stand a certain distance away from a speaker and you hear a certain intensity of sound.  If you double your distance from the speaker, what happens to the sound intensity at your new position?
• A)      drops to 1/2 its original value
• B)      drops to 1/4 its original value
• C)      drops to 1/8 its original value
• D)      drops to 1/16 its original value
• E)      does not change at all

8. You hear a fire truck with a certain intensity, and you are about 1 mile away.   Another person hears the same fire truck with an intensity that is about 10 times less.   Roughly how far is the other person from the fire truck?
• A)      about the same distance
9. When Mary talks, she creates an intensity level of 60 dB at your location.  Alice talks with the same volume, also giving 60 dB at your location.  If both Mary and Alice talk simultaneously from the same spot, what would be the new intensity level that you hear?
• A)      more than 120 dB
• B)     120 dB
• C)      between 60 dB and 120 dB
• D)      60 dB
• E)      less than 60 dB
10. A quiet radio has an intensity level of about 40 dB.   Busy street traffic has a level of about 70 dB.   How much greater is the intensity of the street traffic compared to the radio?
11. Intensity level is given by ฮฒ = 10 log(I/I0) with I0 = 10-12 W/m2.  The usual threshold of human hearing is defined as intensity level of ฮฒ = 0 dB.  What does this actually mean in terms of sound intensity?
• A)      intensity is undefined at that level
• B)      intensity is 100 W/m2
• C)      intensity is 0.0 W/m2
• D)      intensity is 10-12 W/m2
• E)      intensity is 1.0 W/m2
12. You have a long pipe and a short pipe.   Which one has the higher frequency?
• A)      the long pipe
• B)      the short pipe
• C)      both have the same frequency
• D)      depends on the speed of sound in the pipe
13. A wood whistle has a variable length.  You just heard the tone from the whistle at maximum length.  If the air column is made shorter by moving the end stop, what happens to the frequency?
• A)      frequency will increase
• B)      frequency will not change
• C)      frequency will decrease
14. If you blow across the opening of a partially filled soda bottle, you hear a tone.  If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change?
• A)      frequency will increase
• B)      frequency will not change
• C)      frequency will decrease
15. You blow into an open pipe and produce a tone.  What happens to the frequency of the tone if you close the end of the pipe and blow into it again?
• A)      depends on the speed of sound in the pipe
• B)      you hear the same frequency
• C)      you hear a higher frequency
• D)      you hear a lower frequency
16. When you tune a guitar string, what physical characteristic of the string are you actually changing?
• A)      the tension in the string
• B)      the mass per unit length of the string
• C)      the composition of the string
• D)      the overall length of the string
• E)      the inertia of the string
17. Speakers A and B emit sound waves of ฮป = 1 m, which interfere constructively at a donkey located far away (say, 200 m).   What happens to the sound intensity if speaker A steps back 2.5 m?
• A)      intensity increases
• B)      intensity stays the same
• C)      intensity goes to zero
• D)      impossible to tell
18. The traces below show beats that occur when two different pairs of waves interfere.  For which case is the difference in frequency of the original waves greater?
• A)      pair 1
• B)      pair 2
• C)      same for both pairs
• D)      impossible to tell by just looking
19. Observers A, B, and C listen to a moving source of sound.  The location of the wave fronts of the moving source with respect to the observers is shown below.  Which of the following is true?
• A)      frequency is highest at A
• B)      frequency is highest at B
• C)      frequency is highest at C
• D)      frequency is the same at all three points
20. You are heading toward an island in a speedboat and you see your friend standing on the shore, at the base of a cliff.  You sound the boatโs horn to alert your friend of your arrival.  If the horn has a rest frequency of f0, what frequency does your friend hear?
• A)      lower than f0
• B)      equal to f0
• C)      higher than f0
21. In the previous question, the horn had a rest frequency of f0, and we found that your friend heard a higher frequency f1 due to the Doppler shift.  The sound from the boat hits the cliff behind your friend and returns to you as an echo.  What is the frequency of the echo that you hear?
• A)      lower than f0
• B)      equal to f0
• C)      higher than f0 but lower than f1       D)      equal to f1
• E)      higher than f1
credit: Giancoli Physicsยฉ2013 www.PinoyBIX.com

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