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Old-Examination-Questions-Ch.#17 (Dr. Gondal -Phys102)
T081
Q5.A pipe has two consecutive resonance frequencies of 600 Hz and 1000 Hz. One end of the pipe is closed. What is the fundamental frequency of the pipe? (Ans: 200 Hz)
Q6.The intensity of sound emitted by a source is doubled. What is the change in intensity level of the sound? (Ans: 3.0 dB)
Q7.Two identical loudspeakers, facing eachother, are in phase and each has a frequency of 85 Hz. A man at the midpoint between the two loudspeakers moves slowly toward one of them until he hears the first minimum in sound. How far did he move? (The speed of sound in air = 340 m/s) (Ans: 1.0 m)
Q8.If it were possible for a man to move with the speed of sound directly toward a stationary whistle emitting a sound of frequency f, he wouldhear (Ans: a sound of frequency 2f)
T072
Q6.
Two speakers S1 and S2 are placed on the y-axis as shown in figure 1. The speakers are in phase and emit identical sound waves with a given frequency. An observer, standing at point A, hears a sound of maximum intensity. As the observer moves along a straight line parallel to the y-axis and reaches point B, he hears first minimum of sound intensity.The frequency of sound emitted by the speakers is? (speed of sound in air = 343 m/s). (Ans: 121 Hz)
Q7. A stationary train passenger hears a frequency of 520 Hz as a train approaches a bell on a trackside safety gate. After the train passes the gate the passenger hears a frequency of 480 Hz for the bell sound. The speed of the train is : ( speed of sound in air = 343 m/s) (Ans: 13.7 m/s)
Q8: Theintensity of a certain sound wave is 6 mW/cm2. If its sound level is raised by 10 decibels, the new intensity (in mW/cm2) is: (Ans: 60)
Q9. If the speed of sound is 340 m/s, the two lowest resonance frequencies of a 0.5 m organ pipe, closed at one end, are approximately: (Ans: 170 and 510 Hz)
T071
Q#5. In the figure below, two speakers are driven by the same generator and are a distance of 1.0m apart. The speakers emit sound waves at a frequency of 686 Hz that are in phase. A listener starts at A and moves toward B. What will be the distance from A of the first point at which he will observe constructive interference? The speed of sound in air is 343 m/s. (Ans: 0.25 m)
Q#6. A standing wave is set up in an air-filled tube that is closed at one end. The standing wave has two nodes andthe frequency of oscillation is 230 Hz. What is the length of the tube? Take the speed of sound to be 343 m/s. (Ans: 1.1 m)
Q#7. The average output power of a speaker is 550 watts. The sound level that reaches to a detector is 105 dB, how far is the detector from the source? (Take Io=10-12 W/m2) (Ans: 37 m)
Q#8. A stationary policeman sends a sound wave of frequency 550 Hz towards a carapproaching him. The reflected frequency detected by the policeman is 620 Hz. What is the speed of the car? (Ans: 20 m)
T062: Q6. A 2.5 m long tube, open at both ends, is filled with a gas. The frequency of a certain harmonic is 500 Hz and the frequency of the next harmonic is 600 Hz. What is the speed of sound in the tube? (Ans: 500 m/s)
Q7. The intensity of a sound wave of frequency 360 Hz is 1.6×10-6W/m2. .If the speed of sound in air is 343 m/s, what is the displacement amplitude of the air molecules oscillation caused by this wave? (ρair=1.21 kg.m3). (Ans: 3.88×10-8 m )
Q8. A person is listening to sounds from two different sources simultaneously. One source has sound level of 80 dB, while the other has 90 dB. What combined sound level will the person hear? (Ans: 90.4 dB)
Q9. Two trucksare heading straight toward each other with the same speed "U". The horn of one, with frequency, is blowing, and is heard to have a frequency of 3200 Hz by the people in the other truck. Find "U" if the speed of sound is 340 m/s. (Ans: 11 m/s)
T061
Q#5. Sound waves of frequency 340 Hz are sent into the top of a vertical tube containing water, as shown in the figure 1. If standing waves are...

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