Chapter 13 Review Sound

1. What type of waves are sound waves?

Sound waves are longitudinal (compression) waves.

2. What is the area of a longitudinal wave where the particles are closer together than normal? Where the particles are further apart than normal?

Closer together - compressions Further apart – rarefactions

3. Doubling the distance from a sound source changes the intensity by what factor? Tripling the distance? Quadrupling the distance?

Inverse square law. Doubling the distance decreases the intensity by a factor of four. Tripling decreases it by a factor of nine. Quadrupling decreases it by a factor of sixteen.

4. What is the number of cycles per unit time? How is this property heard?

Cycles per second is frequency. Frequency is heard as pitch.

5. The frequency of a sound wave produces what property of sound?

I already told you, it’s PITCH!

6. The amplitude of a sound wave produces what property of sound?

Amplitude is heard as intensity or loudness.

7. The mixture of harmonics produces what property of sound?

Mixture of harmonics is heard as quality or timbre.

8. What three properties of the medium affect sound speed and what effect do they have?

Temperature, density and elasticity. They are all directly related to sound speed. As the property is increased, the sound speed increases.

9. If you are standing at the train station, how does the pitch of the train whistle change as the train passes you?

It changes from a higher pitch to a lower pitch due to the Doppler effect.

10. If you are on the train, how does the pitch of the train whistle change as the train moves?

The pitch doesn’t change. You are not moving relative to the train whistle.

11. What types of waves demonstrate the Doppler Effect?

All types of waves exhibit the Doppler effect.

12. A car passes you at a constant speed with the horn sounding. How does the pitch change? Is the change gradual or sudden?

The pitch suddenly drops from higher than the produced pitch to lower than the produced pitch.

13. How many beats are produced if a sound of frequency 256 Hz and 248 Hz are produced simultaneously?

256 – 248 = 8 Hz

14. If the frequency of a sound wave matches the natural frequency of an object, what condition results?

Resonance

15. What property of sound allows a singer to break a wine glass with her voice?

Resonance

16. Why are tall buildings so susceptible to earthquakes?

The natural resonant frequency of the building matches the frequency of the earthquake waves.

17. If a violin string has a fundamental frequency of 400 Hz, what are the frequencies of the second and third harmonics?

2 nd 800 Hz 3 rd 1200 Hz

18. What harmonics are produced by a pipe open at both ends?

All the harmonics of the fundamental are present in a tube open on both ends.

19. What harmonics are produced by a pipe closed at one end?

Only the ODD harmonics of the fundamental are present in a tube closed on one end.

20. Find three frequencies that will resonate in a 3 m length of pipe open at both ends. Assume the speed of sound is 340 m/s.

The fundamental wavelength of an open pipe is two times the length of the tube. = 3 x 2 = 6 m v = f  340 = f x 6 f = 57 Hz (fundamental) Since an open tube has all harmonics: 2 nd = 57 x 2 = 114 Hz 3 rd = 57 x 3 = 171 Hz, etc.

21. Find three frequencies that will resonate in a 3 m length of pipe closed at one end. Assume the speed of sound is 340 m/s.

The fundamental wavelength of a closed pipe is four times the length of the tube. = 3 x 4 = 12 m v = f  340 = f x 12 f = 28 Hz (fundamental) Since a closed tube has only the odd harmonics: 3rd = 28 x 3 = 84 Hz 5 th = 28 x 5 = 140 Hz, etc.

22. Find three frequencies that will resonate in a 50 cm length of pipe open at both ends. Assume the speed of sound is 340 m/s.

The fundamental wavelength of an open pipe is two times the length of the tube. = 0.5 x 2 = 1 m v = f  340 = f x 1 f = 340 Hz (fundamental) Since an open tube has all harmonics: 2 nd = 340 x 2 = 680 Hz 3 rd = 340 x 3 = 1020 Hz, etc.

23. Find three frequencies that will resonate in a 50 cm length of pipe closed at one end. Assume the speed of sound is 340 m/s.

The fundamental wavelength of a closed pipe is four times the length of the tube. = 0.5 x 4 = 2 m v = f  340 = f x 2 f = 170 Hz (fundamental) Since a closed tube has only the odd harmonics: 3rd = 170 x 3 = 510 Hz 5 th = 170 x 5 = 850 Hz, etc.