Lecture 7- Sound Waves Chapter 17

Transcription

1 Admin Wave Speed Questions 1 / 10 Lecture 7- Sound Waves Chapter 17 Prof. Noronha-Hostler PHY-124H HONORS ANALYTICAL PHYSICS IB Phys- 124H March 2 nd, 2018

2 Admin Wave Speed Questions 2 / 10 Housekeeping Homework 8 due 3/19/18 (because of lab) Projected grades on GradeBook. Have not yet dropped lowest homeworks/labs (only at the end) Shortened office hours (until 10:20am today).

3 Admin Wave Speed Questions 3 / 10 Recall the velocity of a string

4 Admin Wave Speed Questions 4 / 10 Derivation of speed of sound

5 Admin Wave Speed Questions 5 / 10 Sound through a tube

6 Admin Wave Speed Questions 6 / 10 Instrument size

7 Admin Wave Speed Questions 7 / 10 Beats

8 Admin Wave Speed Questions 8 / 10 Doppler Effect Train Whistle

9 Admin Wave Speed Questions 9 / 10 Beats

10 Admin Wave Speed Questions 10 / 10 Mach Cone

11 You are observing a thunderstorm. In the distance, you see a flash of lightning. Five seconds later, you hear thunder. How far away was the lightning flash? a) 1 mile (1.6 km) b) 0.5 mile (0.8 km) c) 2 miles (3.2 km) d) 0.25 mile (0.4 km) e) 5 miles (8.0 km)

12 You are observing a thunderstorm. In the distance, you see a flash of lightning. Five seconds later, you hear thunder. How far away was the lightning flash? a) 1 mile (1.6 km) b) 0.5 mile (0.8 km) c) 2 miles (3.2 km) d) 0.25 mile (0.4 km) e) 5 miles (8.0 km)

13 In a classroom demonstration, a physics professor breathes in a small amount of helium and begins to talk. The result is that the professor s normally low, baritone voice sounds quite high pitched. Which one of the following statements best describes this phenomena? a) The presence of helium changes the speed of sound in the air in the room, causing all sounds to have higher frequencies. b) The professor played a trick on the class by tightening his vocal cords to produces higher frequencies in his throat and mouth than normal. The helium was only a distraction and had nothing to do with it. c) The helium significantly alters the vocal chords causing the wavelength of the sounds generated to decrease and thus the frequencies increase. d) The wavelength of the sound generated in the professor s throat and mouth is only changed slightly, but since the speed of sound in helium is approximately 2.5 times larger than in air, therefore the frequencies generated are about 2.5 times higher.

14 In a classroom demonstration, a physics professor breathes in a small amount of helium and begins to talk. The result is that the professor s normally low, baritone voice sounds quite high pitched. Which one of the following statements best describes this phenomena? a) The presence of helium changes the speed of sound in the air in the room, causing all sounds to have higher frequencies. b) The professor played a trick on the class by tightening his vocal cords to produces higher frequencies in his throat and mouth than normal. The helium was only a distraction and had nothing to do with it. c) The helium significantly alters the vocal chords causing the wavelength of the sounds generated to decrease and thus the frequencies increase. d) The wavelength of the sound generated in the professor s throat and mouth is only changed slightly, but since the speed of sound in helium is approximately 2.5 times larger than in air, therefore the frequencies generated are about 2.5 times higher.

15 A particle of dust is floating in the air approximately one half meter in front of a speaker. The speaker is then turned on produces a constant pure tone of 226 Hz, as shown. The sound waves produced by the speaker travel horizontally. Which one of the following statements correctly describes the subsequent motion of the dust particle, if any? a) The particle of dust will oscillate left and right with a frequency of 226 Hz. b) The particle of dust will oscillate up and down with a frequency of 226 Hz. c) The particle of dust will be accelerated toward the right and continue moving in that direction. d) The particle of dust will move toward the right at constant velocity. e) The dust particle will remain motionless as it cannot be affected by sound waves.

16 A particle of dust is floating in the air approximately one half meter in front of a speaker. The speaker is then turned on produces a constant pure tone of 226 Hz, as shown. The sound waves produced by the speaker travel horizontally. Which one of the following statements correctly describes the subsequent motion of the dust particle, if any? a) The particle of dust will oscillate left and right with a frequency of 226 Hz. b) The particle of dust will oscillate up and down with a frequency of 226 Hz. c) The particle of dust will be accelerated toward the right and continue moving in that direction. d) The particle of dust will move toward the right at constant velocity. e) The dust particle will remain motionless as it cannot be affected by sound waves.

17 Two identical speakers are emitting a constant tone that has a wavelength of 0.50 m. Speaker A is located to the left of speaker B. At which of the following locations would complete destructive interference occur? a) 2.15 m from speaker A and 3.00 m from speaker B b) 3.75 m from speaker A and 2.50 m from speaker B c) 2.50 m from speaker A and 1.00 m from speaker B d) 1.35 m from speaker A and 3.75 m from speaker B e) 2.00 m from speaker A and 3.00 m from speaker B

18 Two identical speakers are emitting a constant tone that has a wavelength of 0.50 m. Speaker A is located to the left of speaker B. At which of the following locations would complete destructive interference occur? a) 2.15 m from speaker A and 3.00 m from speaker B b) 3.75 m from speaker A and 2.50 m from speaker B c) 2.50 m from speaker A and 1.00 m from speaker B d) 1.35 m from speaker A and 3.75 m from speaker B e) 2.00 m from speaker A and 3.00 m from speaker B

19 Natalie is a distance d in front of a speaker emitting sound waves. She then moves to a position that is a distance 2d in front of the speaker. By what percentage does the sound intensity decrease for Natalie between the two positions? a) 10 % b) 25 % c) 50 % d) 75% e) The sound intensity remains constant because it is not dependent on the distance.

20 Natalie is a distance d in front of a speaker emitting sound waves. She then moves to a position that is a distance 2d in front of the speaker. By what percentage does the sound intensity decrease for Natalie between the two positions? a) 10 % b) 25 % c) 50 % d) 75% e) The sound intensity remains constant because it is not dependent on the distance.

21 A girl is playing a trumpet. The sound waves produced are traveling through air to your ear. Which one of the following statements is false concerning this situation? a) A high-frequency sound that the trumpet produces is interpreted as a highpitched sound. b) Air molecules between the trumpet and your ear vibrate back and forth parallel to the direction the waves are traveling. c) The loudness of the sound wave involves the size of the oscillations in air pressure. d) The sounds from the trumpet are longitudinal waves. e) The sound travels at the speed of light to your ear.

22 A girl is playing a trumpet. The sound waves produced are traveling through air to your ear. Which one of the following statements is false concerning this situation? a) A high-frequency sound that the trumpet produces is interpreted as a highpitched sound. b) Air molecules between the trumpet and your ear vibrate back and forth parallel to the direction the waves are traveling. c) The loudness of the sound wave involves the size of the oscillations in air pressure. d) The sounds from the trumpet are longitudinal waves. e) The sound travels at the speed of light to your ear.

23 A soft drink bottle is 15 cm tall. Joey blows across that top of the bottle just after drinking the last of his drink. What is the approximate fundamental frequency of the tone that Joey generates? a) 230 Hz b) 570 Hz c) 680 Hz d) 810 Hz e) 1100 Hz

24 A soft drink bottle is 15 cm tall. Joey blows across that top of the bottle just after drinking the last of his drink. What is the approximate fundamental frequency of the tone that Joey generates? a) 230 Hz b) 570 Hz c) 680 Hz d) 810 Hz e) 1100 Hz

25 A child is swinging back and forth with a constant period and amplitude. Somewhere in front of the child, a stationary horn is emitting a constant tone of frequency f S. Five points are labeled in the drawing to indicate positions along the arc as the child swings. At which position(s) will the child hear the lowest frequency for the sound from the whistle? a) at B when moving toward A b) at B when moving toward C c) at C when moving toward B d) at C when moving toward D e) at both A and D

26 A child is swinging back and forth with a constant period and amplitude. Somewhere in front of the child, a stationary horn is emitting a constant tone of frequency f S. Five points are labeled in the drawing to indicate positions along the arc as the child swings. At which position(s) will the child hear the lowest frequency for the sound from the whistle? a) at B when moving toward A b) at B when moving toward C c) at C when moving toward B d) at C when moving toward D e) at both A and D