Sheet 3: Ch 3
- A sound wave in air has a pressure amplitude equal to4.00 x 10-3 N/m2. Calculate the displacement amplitude of the wave at a frequency of 10.0 kHz.
2- A sinusoidal sound wave is described by the displacement wave function
(a)Find the amplitude, wavelength, and speed of this wave. (b) Determine the instantaneous displacement from equilibrium of the elements of air at the position x = 0.050 m at t = 3.00 ms. (c) Determine the maximum speed of the element’s oscillatory motion.
3- As a certain sound wave travels through the air, it produces pressure variations (above and below atmospheric pressure) given by ∆P = 1.27 sin(πx - 340πt) in SI units. Find (a) the amplitude of the pressure variations, (b) the frequency, (c) the wavelength in air, and (d) the speed of the sound wave.
4- Write an expression that describes the pressure variation asa function of position and time for a sinusoidal soundwave in air, if ( λ= 0.100 m and ∆Pmax= 0.200 N/m2.( v= 331 m/s)
5- Write the function that describes the displacement wave corresponding to the pressure wave in Problem 4.
6- An experimenter wishes to generate in air a sound wave that has a displacement amplitude of 5.50 x 10-6 m. The pressure amplitude is to be limited to 0.840 N/m2. What is the minimum wavelength the sound wave can have?
7- The intensity of a sound wave at a fixed distance from a speaker vibrating at 1.00 kHz is 0.600 W/m2. (a) Determine the intensity if the frequency is increased to 2.50 kHz while a constant displacement amplitude is maintained. (b) Calculate the intensity if the frequency is reduced to 0.500 kHz and the displacement amplitude is doubled.
8- The intensity of a sound wave at a fixed distance from aspeaker vibrating at a frequency f is I. (a) Determine theintensity if the frequency is increased to f. while a constantdisplacement amplitude is maintained. (b) Calculate theintensity if the frequency is reduced to f/2 and the displacementamplitude is doubled.
9- A train is moving parallel to a highway with a constant speed of 20.0 m/s. A car is traveling in the same direction as the train with a speed of 40.0 m/s. The car horn sounds at a frequency of 510 Hz, and the train whistle sounds at a frequency of 320 Hz. (a) When the car is behind the train, what frequency does an occupant of the car observe for the train whistle? (b) After the car passes and is in front of the train, what frequency does a train passenger observe for the car horn?
10- Standing at a crosswalk, you hear a frequency of 560 Hz from the siren of an approaching ambulance. After the ambulance passes, the observed frequency of the siren is 480 Hz. Determine the ambulance’s speed from these observations.
11- Why are sound waves characterized as longitudinal?
12- If an alarm clock is placed in a good vacuum and then activated,
no sound is heard. Explain.
13- How can an object move with respect to an observer so that the sound from it is not shifted in frequency?
14- Suppose the wind blows. Does this cause a Doppler effectfor sound propagating through the air? Is it like a movingsource or a moving observer?