This set of Engineering Physics Interview Questions and Answers focuses on “Reverberation II”.
1. The volume o an auditorium is 12,000m3. Its reverberation time is 1.5 seconds. If the average absorption coefficient of interior surfaces is 0.4 Sabine/m2. Find the area of interior surfaces.
Explanation: Reverberation time = 0.167V/aS
Total surface area S=3340m2.
2. The intensity of sound produced by roaring of a lion at a distance of 5m is 0.01W/m2. Calculate the intensity level in decibel.
Explanation: Intensity level = 10log0.01/10-12
Intensity level = 100dB.
3. Calculate the intensity level of a plane just leaving the runway having sound intensity of about 1000W/m2.
Explanation: Intensity level = 10log1000/10-12
Intensity level = 150dB.
4. Frequency is used for tuning musical instruments.
Explanation: Musicians use the beat phenomenon in tuning their musical instruments. If an instrument is sounded against a standard frequency and tuned until the beats disappear, then the instrument is in tune with the standard frequency. Therefore beats are used for tuning musical instruments.
5. A tuning fork produces 4 beats/s when sounded with a tuning fork of frequency 512Hz. The same tuning fork, when sounded with a another tuning fork of frequency 514Hz, produces 6 beats/s. Find the frequency of the tuning fork.
Explanation: Let the frequency of tuning fork = v
The fork produces 4 beats/s with a tuning fork of frequency 512Hz
Therefore, v = 512±4 = 516Hz or 508Hz
The fork also produces 6 beats/s with a tuning fork of frequency 514Hz
Therefore, v = 514±6 = 520Hz or 508Hz
508Hz is common in both cases. Therefore, the frequency of the tuning fork is 508Hz.
6. When a train, blowing its whistle, approaches him, the pitch of the whistle appears to rise and it appears to drop as the engine moves away from him. What is the effect observed here?
a) Doppler effect
b) Frequency effect
d) Echelon effect
Explanation: Whenever there is a relative motion between the source, the observer and the medium, the frequency of sound emitted by the source as received by the observer is different from the frequency of sound emitted by the source. The apparent change in frequency when the source, the observer and the medium are in motion is called Doppler effect.
7. In which of the following is the Doppler Effect symmetric?
Explanation: Doppler effect is said to be asymmetric. However, Doppler effect in light is symmetric. This is because sound or mechanical waves in general, have a velocity relative to the medium through which they travel whereas light or electromagnetic waves travel quiet and independent of it.
8. What will be the velocity of sound in a perfectly rigid rod?
Explanation: The velocity of sound in a perfectly rigid body will be infinite because the value of Young’s modulus of elasticity is infinite for a perfectly rigid rod.
9. The speed of sound in moist air is greater than that in dry air.
Explanation: The density of water vapour is less than that of air. So the density of air mixed with water vapour is less than that of dry air. Hence the speed of sound in moist air is greater than that in dry air.
10. The sound of a bomb explosion travels faster than the sound produced by a humming bee.
Explanation: The velocity of sound in a medium does not depend upon its loudness, pitch or quality. Thus the sound of a bomb explosion and the sound produced by humming bee, even though having entirely different characteristics, travel with the same speed.
11. When can sound be heard over long distances?
a) On a sunny day
b) On a humid day
c) When snowing
d) On a rainy day
Explanation: On a rainy day, the air contains a larger amount of water vapour. This decreases the density of air. As a result, the sound travels faster in the air and can be heard over longer distances.
12. A person riding on a merry-go round emits a sound wave of a certain frequency. Will the person at centre observe Doppler Effect.
Explanation: The person does not experience the Doppler Effect because the source is moving perpendicular to the line joining the source and the observer.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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