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SOUND WAVES
QUESTIONS FOR SHORT ANSWER
1. If you are walking on the moon, can you hear the sound of stones cracking behind you? Can you hear the sound of your own footsteps?
ANSWER: Since there is no air on the moon, there is the absence of a medium in which the cracking stones would set vibrations. The vibrations of the stones can not propagate in absence of a medium. So the sound of the stones cracking behind cannot be heard. In fact, no sound is produced. But this answer is on the assumption that our ears are open to the environment like on the earth which is not correct. In the absence of the air, there is no atmospheric pressure of which we are accustomed to. It will damage our body and ears. So we need space suits which isolates the whole body from the surrounding.
The sound of own footsteps can be heard because the vibrations produced can travel through our body to the ears.
2. Can you hear your own words if you are standing in a perfect vacuum? Can you hear your friend in the same conditions?
ANSWER: When we speak the vocal cords in our throat vibrate. These vibrations reach our ears internally. So even in a perfect vacuum, we can hear our own words.
But in the same conditions, we cannot hear our friend due to the absence of a medium which allows propagating the vibrations from one point to the other.
3. A vertical rod is hit at one end. What kind of wave propagates in the rod if (a) the hit is made vertically (b) the hit is made horizontally?
ANSWER: (a) The vertical hit will set the particles at that end to vibrate longitudinally, This longitudinal disturbance propagates as a longitudinal wave in the rod.
(b) The horizontal hit will set the particles at that end to vibrate along the perpendicular to the axis of the rod. So the disturbance will propagate as a transverse wave in the rod.
4. Two loudspeakers are arranged facing each other at some distance. Will a person standing behind one of the loudspeakers clearly hear the sound of the other loudspeaker or the clarity will be seriously damaged because of the "collision" of the two sounds in between?
ANSWER: The loudspeakers have very high intensity in the front direction but not so high in the backward direction. In the given condition let us assume that both loudspeakers are connected to the same source. The person behind the first loudspeaker will hear comparatively very low-intensity sound from it than the other one if the distance between the loudspeakers is small. Even if their sound interferes either constructively or destructively at the ears of the person, he will hear the sound clearly. But if the distance between the loudspeakers is large, the intensity of the other loudspeaker will be comparable to the first one, also due to the path difference both sources will have a phase difference and the clarity of the sound will be seriously affected.
5. The voice of a person, who has inhaled helium, has a remarkably high pitch. Explain on the basis of the resonant vibration of the vocal cord filled with air and with helium.
ANSWER: The resonant frequency of the vocal cord in the voice box is directly proportional to the speed of the sound. The voice box of a person inhaling helium has helium-filled in it. The speed of sound in helium is about three times more than in the air. Hence the resonant frequency is higher in this case. Therefore his voice will be of high pitch.
6. Draw a diagram to show the standing pressure wave and standing displacement wave for the 3rd overtone mode of vibration of an open organ pipe.
ANSWER: Frequencies for a standing wave in an open organ pipe is given by, ν = nV/2L, where n = 1, 2, 3, .....
n = 1 is for the fundamental mode of vibration. For the 3rd overtone mode of vibration n = 4, and the corresponding frequency
ν = 4V/2L. It will have four pressure antinodes. Corresponding to these antinodes there will be four displacement nodes. The diagram is the following:-
Diagram for Q - 6
7. Two tuning forks vibrate with the same amplitude but the frequency of the first is double the frequency of the second. Which fork produces more intense sound in air?
ANSWER: The amplitudes of both tuning forks are same hence both will produce same displacement amplitudes in the sound wave in the air say s₀. Corresponding pressure amplitudes
p₀ = B⍵s₀/V =B*2πν*s₀/V =(2πBs₀/V)ν
Since the intensity of sound is proportional to the square of the pressure amplitude p₀, but p₀ is proportional to the frequency ν hence the intensity of the sound is also proportional to the square of the frequency. Hence the first tuning fork having double frequency will produce more intense sound in air.
8. In discussing the Doppler effect, we use the word "apparent frequency". Does it mean that the frequency of the sound is still that of the source and it is some physiological phenomenon in the listener's ear that gives rise to the Doppler effect? Think for the observer approaching the source and for the source approaching the observer.
ANSWER: The frequency of the sound remains the same that of the source. The apparent frequency refers to the frequency perceived by the observer due to the relative motion of the observer and the source.
When the observer approaches the source, the time between two consecutive points of the same phase decreases, so he perceives the sound as having a higher frequency than when standing.
When the source approaches the observer again due to the relative motion the second consecutive point of the same phase is produced nearer to the observer, so the two consecutive points of the same phase reach observer in a shorter time than both were not moving. So again the observer perceives the sound as having a higher frequency. This phenomenon is named as Doppler effect.
1. If you are walking on the moon, can you hear the sound of stones cracking behind you? Can you hear the sound of your own footsteps?
ANSWER: Since there is no air on the moon, there is the absence of a medium in which the cracking stones would set vibrations. The vibrations of the stones can not propagate in absence of a medium. So the sound of the stones cracking behind cannot be heard. In fact, no sound is produced. But this answer is on the assumption that our ears are open to the environment like on the earth which is not correct. In the absence of the air, there is no atmospheric pressure of which we are accustomed to. It will damage our body and ears. So we need space suits which isolates the whole body from the surrounding.
The sound of own footsteps can be heard because the vibrations produced can travel through our body to the ears.
2. Can you hear your own words if you are standing in a perfect vacuum? Can you hear your friend in the same conditions?
ANSWER: When we speak the vocal cords in our throat vibrate. These vibrations reach our ears internally. So even in a perfect vacuum, we can hear our own words.
But in the same conditions, we cannot hear our friend due to the absence of a medium which allows propagating the vibrations from one point to the other.
3. A vertical rod is hit at one end. What kind of wave propagates in the rod if (a) the hit is made vertically (b) the hit is made horizontally?
ANSWER: (a) The vertical hit will set the particles at that end to vibrate longitudinally, This longitudinal disturbance propagates as a longitudinal wave in the rod.
(b) The horizontal hit will set the particles at that end to vibrate along the perpendicular to the axis of the rod. So the disturbance will propagate as a transverse wave in the rod.
4. Two loudspeakers are arranged facing each other at some distance. Will a person standing behind one of the loudspeakers clearly hear the sound of the other loudspeaker or the clarity will be seriously damaged because of the "collision" of the two sounds in between?
ANSWER: The loudspeakers have very high intensity in the front direction but not so high in the backward direction. In the given condition let us assume that both loudspeakers are connected to the same source. The person behind the first loudspeaker will hear comparatively very low-intensity sound from it than the other one if the distance between the loudspeakers is small. Even if their sound interferes either constructively or destructively at the ears of the person, he will hear the sound clearly. But if the distance between the loudspeakers is large, the intensity of the other loudspeaker will be comparable to the first one, also due to the path difference both sources will have a phase difference and the clarity of the sound will be seriously affected.
5. The voice of a person, who has inhaled helium, has a remarkably high pitch. Explain on the basis of the resonant vibration of the vocal cord filled with air and with helium.
ANSWER: The resonant frequency of the vocal cord in the voice box is directly proportional to the speed of the sound. The voice box of a person inhaling helium has helium-filled in it. The speed of sound in helium is about three times more than in the air. Hence the resonant frequency is higher in this case. Therefore his voice will be of high pitch.
6. Draw a diagram to show the standing pressure wave and standing displacement wave for the 3rd overtone mode of vibration of an open organ pipe.
ANSWER: Frequencies for a standing wave in an open organ pipe is given by, ν = nV/2L, where n = 1, 2, 3, .....
n = 1 is for the fundamental mode of vibration. For the 3rd overtone mode of vibration n = 4, and the corresponding frequency
ν = 4V/2L. It will have four pressure antinodes. Corresponding to these antinodes there will be four displacement nodes. The diagram is the following:-
7. Two tuning forks vibrate with the same amplitude but the frequency of the first is double the frequency of the second. Which fork produces more intense sound in air?
ANSWER: The amplitudes of both tuning forks are same hence both will produce same displacement amplitudes in the sound wave in the air say s₀. Corresponding pressure amplitudes
p₀ = B⍵s₀/V =B*2πν*s₀/V =(2πBs₀/V)ν
Since the intensity of sound is proportional to the square of the pressure amplitude p₀, but p₀ is proportional to the frequency ν hence the intensity of the sound is also proportional to the square of the frequency. Hence the first tuning fork having double frequency will produce more intense sound in air.
8. In discussing the Doppler effect, we use the word "apparent frequency". Does it mean that the frequency of the sound is still that of the source and it is some physiological phenomenon in the listener's ear that gives rise to the Doppler effect? Think for the observer approaching the source and for the source approaching the observer.
ANSWER: The frequency of the sound remains the same that of the source. The apparent frequency refers to the frequency perceived by the observer due to the relative motion of the observer and the source.
When the observer approaches the source, the time between two consecutive points of the same phase decreases, so he perceives the sound as having a higher frequency than when standing.
When the source approaches the observer again due to the relative motion the second consecutive point of the same phase is produced nearer to the observer, so the two consecutive points of the same phase reach observer in a shorter time than both were not moving. So again the observer perceives the sound as having a higher frequency. This phenomenon is named as Doppler effect.
ANSWER: Since there is no air on the moon, there is the absence of a medium in which the cracking stones would set vibrations. The vibrations of the stones can not propagate in absence of a medium. So the sound of the stones cracking behind cannot be heard. In fact, no sound is produced. But this answer is on the assumption that our ears are open to the environment like on the earth which is not correct. In the absence of the air, there is no atmospheric pressure of which we are accustomed to. It will damage our body and ears. So we need space suits which isolates the whole body from the surrounding.
The sound of own footsteps can be heard because the vibrations produced can travel through our body to the ears.
2. Can you hear your own words if you are standing in a perfect vacuum? Can you hear your friend in the same conditions?
ANSWER: When we speak the vocal cords in our throat vibrate. These vibrations reach our ears internally. So even in a perfect vacuum, we can hear our own words.
But in the same conditions, we cannot hear our friend due to the absence of a medium which allows propagating the vibrations from one point to the other.
3. A vertical rod is hit at one end. What kind of wave propagates in the rod if (a) the hit is made vertically (b) the hit is made horizontally?
ANSWER: (a) The vertical hit will set the particles at that end to vibrate longitudinally, This longitudinal disturbance propagates as a longitudinal wave in the rod.
(b) The horizontal hit will set the particles at that end to vibrate along the perpendicular to the axis of the rod. So the disturbance will propagate as a transverse wave in the rod.
4. Two loudspeakers are arranged facing each other at some distance. Will a person standing behind one of the loudspeakers clearly hear the sound of the other loudspeaker or the clarity will be seriously damaged because of the "collision" of the two sounds in between?
ANSWER: The loudspeakers have very high intensity in the front direction but not so high in the backward direction. In the given condition let us assume that both loudspeakers are connected to the same source. The person behind the first loudspeaker will hear comparatively very low-intensity sound from it than the other one if the distance between the loudspeakers is small. Even if their sound interferes either constructively or destructively at the ears of the person, he will hear the sound clearly. But if the distance between the loudspeakers is large, the intensity of the other loudspeaker will be comparable to the first one, also due to the path difference both sources will have a phase difference and the clarity of the sound will be seriously affected.
5. The voice of a person, who has inhaled helium, has a remarkably high pitch. Explain on the basis of the resonant vibration of the vocal cord filled with air and with helium.
ANSWER: The resonant frequency of the vocal cord in the voice box is directly proportional to the speed of the sound. The voice box of a person inhaling helium has helium-filled in it. The speed of sound in helium is about three times more than in the air. Hence the resonant frequency is higher in this case. Therefore his voice will be of high pitch.
6. Draw a diagram to show the standing pressure wave and standing displacement wave for the 3rd overtone mode of vibration of an open organ pipe.
ANSWER: Frequencies for a standing wave in an open organ pipe is given by, ν = nV/2L, where n = 1, 2, 3, .....
n = 1 is for the fundamental mode of vibration. For the 3rd overtone mode of vibration n = 4, and the corresponding frequency
ν = 4V/2L. It will have four pressure antinodes. Corresponding to these antinodes there will be four displacement nodes. The diagram is the following:-
|
| Diagram for Q - 6 |
7. Two tuning forks vibrate with the same amplitude but the frequency of the first is double the frequency of the second. Which fork produces more intense sound in air?
ANSWER: The amplitudes of both tuning forks are same hence both will produce same displacement amplitudes in the sound wave in the air say s₀. Corresponding pressure amplitudes
p₀ = B⍵s₀/V =B*2πν*s₀/V =(2πBs₀/V)ν
Since the intensity of sound is proportional to the square of the pressure amplitude p₀, but p₀ is proportional to the frequency ν hence the intensity of the sound is also proportional to the square of the frequency. Hence the first tuning fork having double frequency will produce more intense sound in air.
8. In discussing the Doppler effect, we use the word "apparent frequency". Does it mean that the frequency of the sound is still that of the source and it is some physiological phenomenon in the listener's ear that gives rise to the Doppler effect? Think for the observer approaching the source and for the source approaching the observer.
ANSWER: The frequency of the sound remains the same that of the source. The apparent frequency refers to the frequency perceived by the observer due to the relative motion of the observer and the source.
When the observer approaches the source, the time between two consecutive points of the same phase decreases, so he perceives the sound as having a higher frequency than when standing.
When the source approaches the observer again due to the relative motion the second consecutive point of the same phase is produced nearer to the observer, so the two consecutive points of the same phase reach observer in a shorter time than both were not moving. So again the observer perceives the sound as having a higher frequency. This phenomenon is named as Doppler effect.
===<<<O>>>===
Links to the Chapters
===<<<O>>>===
Links to the Chapters
CHAPTER- 15 - Wave Motion and Waves on a String
OBJECTIVE-II
EXERCISES - Q-1 TO Q-10
EXERCISES - Q-11 TO Q-20
EXERCISES - Q-21 TO Q-30
EXERCISES - Q-31 TO Q-40
EXERCISES - Q-41 TO Q-50
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
EXERCISES- Q1 TO Q10
EXERCISES- Q11 TO Q20
EXERCISES- Q21 TO Q30
EXERCISES- Q31 TO Q40
EXERCISES- Q41 TO Q50
EXERCISES- Q51 TO Q58 (2-Extra Questions)
CHAPTER- 11 - Gravitation
EXERCISES -Q 31 TO 39
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 15 - Wave Motion and Waves on a String
EXERCISES - Q-1 TO Q-10
EXERCISES - Q-11 TO Q-20
EXERCISES - Q-21 TO Q-30
EXERCISES - Q-31 TO Q-40
EXERCISES - Q-41 TO Q-50
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
EXERCISES- Q11 TO Q20
EXERCISES- Q21 TO Q30
EXERCISES- Q31 TO Q40
EXERCISES- Q41 TO Q50
EXERCISES- Q51 TO Q58 (2-Extra Questions)
CHAPTER- 11 - Gravitation
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 8 - Work and Energy
Click here for → Question for Short Answers
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → Exercises (1-10)
Click here for → Question for Short Answers
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → Exercises (1-10)
Click here for → Exercises (11-20)
Click here for → Exercises (21-30)
Click here for → Exercises (31-42)
Click here for → Exercise(43-54)
Click here for → Exercises (21-30)
Click here for → Exercises (31-42)
Click here for → Exercise(43-54)
Click here for → Exercises (31-42)
Click here for → Exercise(43-54)
CHAPTER- 7 - Circular Motion
Click here for → Questions for Short Answer
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → EXERCISES (11-20)
Click here for → EXERCISES (21-30)
CHAPTER- 6 - Friction
Click here for → Questions for Short Answer
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → EXERCISES (11-20)
Click here for → EXERCISES (21-30)
Click here for → OBJECTIVE-I
Click here for → OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → EXERCISES (11-20)
Click here for → EXERCISES (21-30)
CHAPTER- 6 - Friction
Click here for → Questions for Short Answer
Click here for → Questions for Short Answer
Click here for → OBJECTIVE-I
Click here for → Friction - OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → Exercises (11-20)
Click here for → EXERCISES (21-31)
For more practice on problems on friction solve these- "New Questions on Friction".
Click here for → OBJECTIVE-I
Click here for → Friction - OBJECTIVE-II
Click here for → EXERCISES (1-10)
Click here for → Exercises (11-20)
Click here for → EXERCISES (21-31)
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CHAPTER- 5 - Newton's Laws of Motion
Click here for → QUESTIONS FOR SHORT ANSWER
Click here for → QUESTIONS FOR SHORT ANSWER
Click here for→ Newton's laws of motion - Objective - I
Click here for → Newton's Laws of Motion - Objective -II
Click here for → Newton's Laws of Motion-Exercises(Q. No. 1 to 12)
Click here for→ Newton's laws of motion - Objective - I
Click here for → Newton's Laws of Motion - Objective -II
Click here for → Newton's Laws of Motion-Exercises(Q. No. 1 to 12)
Click here for→Newton's Laws of Motion,Exercises(Q.No. 13 to 27)
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CHAPTER- 4 - The Forces
The Forces-
"Questions for short Answers"
Click here for "The Forces" - OBJECTIVE-I
Click here for "The Forces" - OBJECTIVE-II
Click here for "The Forces" - Exercises
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CHAPTER- 3 - Kinematics - Rest and Motion
Click here for "Questions for short Answers"
Click here for "OBJECTIVE-I"
Click here for EXERCISES (Question number 1 to 10)
Click here for EXERCISES (Question number 11 to 20)
Click here for EXERCISES (Question number 21 to 30)
Click here for EXERCISES (Question number 31 to 40)
Click here for EXERCISES (Question number 41 to 52)
CHAPTER- 2 - "Vector related Problems"
CHAPTER- 2 - "Vector related Problems"
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