University Physics Wolfgang Bauer Gary Westfall Chapter 16
University Physics Wolfgang Bauer Gary Westfall Chapter 16 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.
16. 1 In-Class Exercise You are in the middle of a concert hall that is 120. 0 m deep. What is the time difference between the arrival of the sound directly from the orchestra at your position and the arrival of the sound reflected from the back of the concert hall? a) 0. 010 s b) 0. 056 s c) 0. 11 s d) 0. 35 s e) 0. 77 s
16. 2 In-Class Exercise A teenager is using a new cell phone ring tone with a frequency of 17 k. Hz. The hearing threshold for a typical teenager at this frequency is 30 d. B, and that for an adult might be 100 d. B. Thus, the teenager’s cell phone ring is audible only to teenagers and not to adults at distances of several meters. How close would an adult need to be to the cell phone to hear it ring if the teenager can hear it at a distance of 10. 0 m? a) 0. 32 cm b) 4. 5 cm c) 8. 9 cm d) 25 cm e) 3. 0 m
16. 3 In-Class Exercise Consider the case of a stationary observer and a source moving with constant velocity (less than the speed of sound) and emitting a sound of frequency f. If the source moves towards the observer, equation 16. 14 predicts a higher observed frequency, f+. If the source moves away from the observer, a lower frequency f - results. Let’s call the difference between the higher frequency and the original frequency Δ+, and the difference between the original frequency and the lower frequency Δ- : Δ+ = f + - f and Δ- = f - f-. Which statement about the frequency differences is correct? a) Δ+ > Δb) Δ+ = Δc) Δ+ < Δd) It depends on the original frequency f. e) It depends on the source velocity v.
16. 4 In-Class Exercise Now consider the case of a stationary source emitting a sound of frequency f and an observer moving with constant velocity (less than the speed of sound). If the observer moves towards the source, equation 16. 15 predicts a higher observed frequency, f+. If the observer moves away from the source, a lower frequency, f -, results. Let’s call the difference between the higher frequency and the original frequency Δ+ and the difference between the original frequency and the lower frequency Δ- : Δ+ = f+ - f and Δ- = f -. Which statement about the frequency differences is correct? a) Δ+ > Δb) Δ+ = Δc) Δ+ < Δd) It depends on the original frequency f. e) It depends on the source velocity v.
16. 5 In-Class Exercise Suppose a source emitting a sound with frequency f moves to the right (in positive x-direction) with a speed of 30 m/s. An observer is located to the right of the source and also moves to the right (in the positive x-direction) with a speed of 50 m/s. The observed frequency, fo, will be ___ the original frequency, f. a) lower than b) the same as c) higher than
16. 6 In-Class Exercise Suppose a source emitting a sound with frequency f moves to the right (in the positive x -direction) with a speed of 30 m/s. An observer is located to the right of the source and also moves to the right (in the positive x direction) with a speed of 50 m/s. Which of the following is the correct expression for the observed frequency fo? a) b) c) d)
16. 7 In-Class Exercise What is the maximum cruise speed of the Concorde at 60, 000 ft? a) 665 mph b) 834 mph c) 1350 mph d) 2130 mph e) 3450 mph
16. 8 In-Class Exercise The half-liter bottle in Figure 16. 25 contains air above the liquid. How would the frequency change if the air in the bottle were replaced with krypton gas? (Hint: Table 16. 1 may help. ) a) It would be lower. b) It would stay the same. c) It would be higher.
Answer Key – Chapter 16 16. 1 d 16. 2 a 16. 3 a 16. 4 b 16. 5 a 16. 6 a 16. 7 c 16. 8 a
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