Selina Concise Class 10 Physics Solution Chapter No. 7- ‘Sound’ For ICSE Board Students.
Selina Concise Class 10 Physics Chapter 7 Sound Exercise All Questions and Answers by Physics Teacher here in this post.
Exercise 7 (a)
Question: 1
What are mechanical waves?
Solution: Mechanical waves are the waves that require material medium to transfer energy.
Question: 2
Define the following terms in relation to a wave:
(a) amplitude
(b) frequency
(c) wavelength and
(d) wave velocity
Solution:
(a) Amplitude is distance between resting position to maximum displacement.
(b) Frequency is the number of waves passing through a certain point per second.
(c) The distance travelled by a wave in a one vibration is called as wavelength.
(d) The distance travelled by wave in one second is called as wave velocity.
Question: 3
A wave passes from one medium to another medium. Mention one property of the wave out of speed, frequency or wavelength (i) which changes, (ii) which does not change.
Solution:
(i) A wave passes through one medium to another property that changes is velocity of the wave
(ii) And the proper that does not change is the frequency of wave.
Question: 4
State two factors on which the speed of a wave travelling in a medium depends.
Solution: The speed of wave depends upon the elasticity and density of the medium.
Question: 5
State two differences between the light and sound waves.
Solution:
Light waves |
Sound waves |
They are electromagnetic waves. | These are mechanical waves. |
The speed of light waves is very high | Speed of sound waves is low compared to light waves. |
Question: 6
What do you mean by reflection of sound? State one condition for the reflection of a sound wave. Name a device in which reflection of a sound wave is used.
Solution: The return of a sound wave on striking a rigid surface back in the same direction is called as reflection of sound waves. Only condition for reflection of sound waves is surface on which sound waves reflect must be bigger than the wavelength of sound wave. Sound reflection is used in sound board and ear trumpet.
Question: 7
What is meant by an echo? State two conditions necessary for an echo to be heard distinctly.
Solution: The sound heard after reflection from a distance surface or obstacle after original sound is gone, is called echo.
To hear echo distinctly following conditions must be satisfied:
(1) Minimum distance from the source of sound and reflector in air must be 17m.
(2) The size of the reflector must be large enough as compared to the wavelength of the sound.
Question: 8
A man is standing at a distance of 12m from a cliff. Will he be able to hear a clear echo of his sound? Give a reason for your answer.
Solution: If a man standing at distance of 12m from a cliff will not be able to hear echo as the minimum distance required to hear echo is 17 m in air.
Question: 9
State two applications of echo.
Solution: Echo is used by bats and dolphins for navigation.
Echo is also used for SONAR which is sound navigation and ranging.
Question: 10
Explain how the speed of sound can be determined by the method of echo?
Solution: Speed of sound can be determined by the method of echo by formula
Velocity = total distance travelled / time interval
Question: 11
State the use of echo by a bat, dolphin and fisherman.
Solution: Bat use echo for navigation as they travel at speed much less than to the speed of sound the sound emitted gets reflected from the obstacles and can be detected by the bats and can change the direction.
Dolphins detects their enemies and obstacles by emitting ultrasonic waves and hearing there echo.
A fisherman use a device that emits ultrasonic waves which come back to that device by reflecting from the spool of fish then that fisherman can calculate the distance of the spool of fish using formula
Distance = velocity of waves x time interval / 2
Question: 12
How do bats avoid obstacles in their way, when in flight?
Solution: Bat use echo for navigation as they travel at speed much less than to the speed of sound the sound emitted gets reflected from the obstacles and can be detected by the bats and can change the direction.
Question: 13
What is meant by sound ranging? Give one use of sound ranging.
Solution: Sound ranging is the process of detecting obstacles using echo is called as sound ranging. The bats and dolphin use sound ranging.
Question: 14
Name the waves used for sound ranging. State one reason for their use. Why are the waves mentioned by you not audible to us?
Solution: Ultrasonic waves are used for sound ranging. The frequency of the ultrasonic waves is more than 20000 Hz. And human ear can hear between 20 Hz to 20000 Hz.
Question: 15
What is ‘SONAR’? State the principle on which it is based.
Solution: SONAR is Sound navigation and ranging. The principle of sonar in which ultrasonic waves are sent in sea water in all directions from the ship. These waves are received after reflection from the obstacle and to measure the distance following formula is used
Distance = velocity of wave x time interval / 2
Question: 16
State the use of echo in the medical field.
Solution: Echo are used in the medical field in ultrasonography for imaging of human organs and echocardiogram.
Multiple Choice Type:
Question: 1
The minimum distance between the source and the reflector in air, to hear an echo, is approximately:
(a) 10 m
(b) 17 m
(c) 34 m
(d) 50 m
Solution: (b) 17 m
Question: 2
To detect obstacles in their path, bats produce:
(a) Infrasonic waves
(b) Ultrasonic waves
(c) Electromagnetic waves
(d) Radio waves
Solution: (b) ultrasonic waves.
Numerical
Question: 1
The wavelength of waves produced on the surface of water is 20cm. If the wave velocity is 24m s-1, calculate (i) the number of waves produced in one second and (ii) the time in which one wave is produced.
Solution: Given
Velocity = 24 m/s
Wavelength = 20 cm = 0.2 m
Frequency = velocity / wavelength
= 24 /0.2
= 120 per second
The time in which one wave is produced = 1/ frequency
= 1/ 120
= 8.3 x 10-3 s.
Question: 2
Calculate the minimum distance in the air required between the source of sound and the obstacle to hear an echo. Take the speed of sound in air = 350m s-1
Solution: Given
Speed of sound in air = 350m/s
Time = 0.1s
As we know,
Distance = velocity x time /2
D= 340 x 0.1 /2 = 17.5m
Question: 3
What should be the minimum distance between the source and reflector in water so that the echo is heard distinctly? (The speed of sound in water = 1400m s-1)
Solution: Given
Velocity of speed in water = 1400 m/s
Time = 0.1 s
As we know,
Distance = velocity x time /2
D = 1400 x 0.1 /2 = 70 m
Question: 4
A man standing 25 m away from a wall produces a sound and receives the reflected sound. (a) Calculate the time after which he receives the reflected sound if the speed of sound in air is 350 m/s-1. (b) Will the man be able to hear a distinct echo? Explain the answer.
Solution: Given
Velocity of sound in air = 350 m/s
Distance = 25 m
Time = distance x 2 / velocity
Time = 25 x 2 / 350
Time = 0.143 s
As the time required to reach the man is 0.1s after the original sound. Man is able to gear the echo.
Question: 5
A RADAR sends a signal to an aeroplane at a distance 300 km away, with a speed of 3 × 108 m s-1. After how much time is the signal received back after reflecting from the aeroplane?
Solution: Given
Distance = 300km = 300000 m
Velocity = 3 x 10 8 m/s
Time = distance x 2 / velocity
Time = 300000 x 2 / 3 x 108
Time = 0.002 s
Question: 6
A man standing 48 m away from a wall fires a gun. Calculate the time after which an echo is heard. (The speed of sound in air is 320m/s-1).
Solution: Given
Distance = 48m
Velocity = 320 m/s
Time = 2 x 48 / 320
Time = 0.3 s.
Question: 7
A ship on the surface of water sends a signal and receives it back from a submarine inside water after 4s. Calculate the distance of the submarine from the ship. (The speed of sound in water is 1450 m s-1).
Solution: Given
Time = 4s
Velocity = 1450 m/s
Distance = time x velocity / 2
D = 4 x 1450 /2
D = 2900 m.
Question: 8
A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears an echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340m s-1, find the distance between the cliff and the observer.
Solution: Given
Frequency = 5 per s
Time for 8 vibrations = 8/5 s
Velocity = 340 m/s
Distance = velocity x time /2
D = 340 x 1.6 /2
D = 272 m
Question: 9
A person standing between two vertical cliffs produces a sound. Two successive echoes are heard at 4s and 6s. Calculate the distance between the cliffs. (Speed of sound in air = 320 m s-1)
Solution: Given
Time interval from cliff 1 = 4s
Time interval from cliff 2 = 6s
Velocity = 320 m/s
Distance of cliff 1 = velocity x time / 2
= 320 x 4 / 2
= 640 m
Distance of cliff 2 = 320 x 6 / 2
= 960 m
Therefore,
Distance between cliffs = 640 + 960
= 1600m
Question: 10
A person standing at a distance x in front of a cliff fires a gun. Another person B standing behind the person A at a distance y from the cliff hears two sounds of the fired shot after 2s and 3s respectively. Calculate x and y (take speed of sound 320 ms-1)
Solution: Given
Velocity = 320 m/s
Time interval = 2s
Time interval from cliff = 3s
Time taken by sound to reach from A to B directly
Distance = velocity x time
(y – x) = 320 x 2
(y – x) = 640m
Time taken by sound after reflection
Distance = velocity x time
(x + y) = 320 x 3
(x + y) = 960m
Therefore, from above equations
2y = 1600
y = 800 m
x = 960 – 800
x = 160m
Question: 11
On sending an ultrasonic wave from a ship towards the bottom of a sea, the time interval between sending the wave and receiving it back is found to be 1.5 s. If the velocity of wave in sea water is 1400 m/s-1, find the depth of sea.
Solution: Given
Velocity = 1400 m/s
Time = 1.5 s
Distance = velocity x time / 2
D = 1400 x 1.5 /2
D = 1050 m
Question: 12
Figure below shows the distance-displacement graph of two waves A and B. Compare (i) the amplitude, (ii) the wavelength of the two waves.
Solution:
Amplitude for A is 10 cm and amplitude for B is 5 cm.
Ratio of amplitude for wave A to wave B = 10:5 = 2:1
Wavelength for wave A is 8 cm and wavelength of wave B is 16 cm.
Ratio of wavelength = 8:16 = 1:2
Exercise 7 (b)
Question: 1
What do you understand by the natural vibrations of a body? Give one example.
Solution: The vibrations occurring in body without any external force are called as natural vibrations of a body.
A load suspended to spring, when stretched and released starts vibrating with its natural frequency.
Question: 2
What is meant by the natural frequency of vibrations of a body? Name one factor on which it depends?
Solution: The vibrations occurring in body without any external force are called as natural vibrations of a body
Natural vibrations of body depend upon it shape and size.
Question: 3
(a) Draw a graph between displacement and time for a body executing the natural vibrations
(b) Where can a body execute the natural vibrations?
Solution:
(a)
(b) The body can execute natural vibrations when force is applied on body and then left it to oscillate in its own natural vibrations.
Question: 4
State one condition for a body to execute natural vibrations.
Solution: A body can execute natural vibrations in vaccum as medium around it can offer some resistance to the free vibrations.
Question: 5
(a) Name one factor on which the frequency of sound emitted due to vibrations in an air column depends.
(b) How does the frequency depend on the factor stated in part (a)?
Solution:
(a) The frequency of sound emitted due to vibration in a air column depends upon length of air column.
(b) Hence, length of column increases the frequency decreases.
Question: 6
State one way of increasing the frequency of a note produced by an air column.
Solution: Frequency is inversely proportional to the length of air column. Hence, by decreasing the length of air column frequency of note produced can be increased.
Question: 7
State two ways of increasing the frequency of vibrations of a stretched string.
Solution: the frequency of vibration of string can be increased by either increasing the tension on the string or by decreasing the length of the string.
Question: 8
How does the frequency of sound given by a stretched string depend on its (a) length, (b) tension?
Solution:
(a) Frequency is inversely proportional to the length of the string.
(b) Frequency is directly proportional to the tension in the string.
Question: 9
What adjustments would you make for tuning a stringed instrument for it to emit a note of a desired frequency?
Solution: frequency is directly proportional to the tension of the string. Hence, to acquire desired frequency tension on the string in the stringed instrument can be varied accordingly.
Question: 10
The diagram below in Fig. shows three ways in which a string of length l in an instrument can vibrate.
(a) Which of the diagram shows the principal note?
(b) Which vibration has a frequency four times that of the first?
(c) Which vibration is of the longest wavelength?
(d) What is the ratio of frequency of vibrations in the diagrams (i) and (ii)?
Solution:
(a) Diagram showing the principle note is (i).
(b) Diagram showing the frequency four times the first is (iii)
(c) Diagram with longest wavelength is (i)
(d) Ration of frequency of vibrations in diagram (i) and (ii) is 1:2.
Question: 11
Explain why strings of different thickness are provided on a stringed instrument.
Solution: The frequency of string is inversely proportional to the radius of the string. Hence, string of different thickness are provided on a stringed instrument.
Question: 12
A blade, fixed at one end, is made to vibrate by pressing its other end and then releasing it. State one way in which the frequency of vibrations of the blade can be lowered.
Solution: To lower the frequency of blade we have to increase the weight of the blade.
Question: 13
How does the medium affect the amplitude of the natural vibrations of a body?
Solution: The amplitude of the natural vibrations decreases gradually as the medium offers resistance to the vibrations.
Question: 14
What are damped vibrations? How do they differ from free vibrations? Give one example of each.
Solution: Damped vibrations are the vibrations of continuously deceasing amplitude to be external force that is actin on the body. Free vibrations can present in only vaccum as medium offers resistance that causes dampening of the vibrations. For example, a pendulum oscillates with decreasing amplitude when air resistance acting on it.
Question: 15
The diagram in figure shows the displacement-time graph of a vibrating body.
(i) Name the kind of vibrations.
(ii) Give one example of such vibrations.
(iii) Why is the amplitude of vibrations gradually decreasing?
(iv) What happens to the vibrations of the body after some time?
Solution:
(i) Damped vibrations.
(ii) A pendulum oscillates with decreasing amplitude when air resistance acting on it.
(iii) The body does work against the forces acting on it. Which results in the decrease in the amplitude of the vibrations.
Question: 16
A tuning fork is vibrating in air. Stat whether the vibrations are natural or damped?
Solution: Tunning fork executes damped vibrations.
Question: 17
Draw a sketch showing the displacement against time for a body executing damped vibrations.
Solution: graph of displacement of a body showing damped vibrations, against time.
Question: 18
What are forced vibrations? Give one example to illustrate your answer.
Solution: The vibrations that are caused by external periodic force are called as forced vibrations. For example, the vibrations produced in the diaphragm of a microphone sound box with frequency corresponding to the speech of the forced vibrations.
Question: 19
On keeping the stem of a vibrating tuning fork on the surface of a table, a loud sound is heard. Give reason.
Solution: When a vibrating tunning force stem is placed on the surface of table it induces forced vibrations on the surface of the table. When the periodic force applied on the body is equal to the natural frequency of the body this phenomenon is called as resonance. When that occurs load sound is heard.
Question: 20
State two differences between the natural and forced vibrations
Solution:
Natural vibrations |
Forced vibrations |
This are the vibrations present in the body without any external force | This are induced vibrations due to external force. |
Frequency of vibrations remains constant. | Frequency of vibrations depends upon the force applied. |
Question: 21
What is meant by resonance? Describe a simple experiment to illustrate the phenomenon of resonance and explain it.
Solution: When the periodic force applied on the body is equal to the natural frequency of the body this phenomenon is called as resonance.
Two tunning forks are mounted on two separate open sound boxes facing each other. When one tunning fork starts vibrating after it stroked on a rubber pad. We will find that other fork also starts vibrating. Reason behind this is when tunning fork vibrates it induces forced vibrations in the sound box which travels to the sound box of other tunning fork. Since the frequency of these vibrations are same as the natural frequency of the fork. The fork peaks up these vibrations and starts vibrating under resonance.
Question: 22
State the condition for the resonance to occur.
Solution: Condition for resonance is the frequency of the forced vibration must be equal to the natural vibrations of the body.
Question: 23
Complete the following sentence:
Resonance is a special case of ______ vibrations, when frequency of the driving force is _______ natural frequency of the driven body.
Solution: Forced, equal.
Question: 24
State two differences between the forced and resonant vibrations
Solution:
Forced vibrations |
Resonant vibrations |
Low amplitude | Very high amplitude |
Natural vibrations of the body are not equal to the forced vibrations. | Natural vibrations of the body equal to the forced vibrations. |
Question: 25
Why is a loud sound is heard at resonance?
Solution: The amplitude of resonance is very high due to coupling of forced and natural vibrations. Hence, loud sound is heard at resonance.
Question: 26
Figure shows two tuning forks A and B of the same frequency mounted on two separate sound boxes with their open ends facing each other. The fork A is set into vibration. (a) Describe your observation. (b) State the principle illustrated by this experiment.
Solution: Two tunning forks named A and B are mounted on two separate open sound boxes facing each other. When fork A start vibrating after it stroked on a rubber pad. We will find that fork B also starts vibrating. Reason behind this is whenfork A vibrates it induces forced vibrations in the sound box which travels to the sound box fork B. Since the frequency of these vibrations are same as the natural frequency of the fork. The fork peaks up these vibrations and starts vibrating under resonance.
Question: 27
In figure A, B, C and D are the four pendulums suspended from the same elastic string XY. The lengths of pendulum A and D are equal, while the length of pendulum B is shorter and of the pendulum C is longer. Pendulum A is set into vibrations.
(a) What is your observation about the vibrations of pendulum D?
(b) Give reason for your observation in part (a).
(c) What type of vibrations take place in pendulums B and C?
(d) Give reason for the answer in part (c)
Solution:
(a) Pendulum D first starts oscillating with small amplitude then acquires same amplitude as A.
(b) As the natural frequencies of pendulumA and D is same when the amplitude of A reaches minimum amplitude of D reaches maximum.
(c) The amplitude of vibrations in B and C is very small.
Question: 28
A vibrating tuning fork, held over an air column of a given length with its one end closed, produces a loud audible sound. Name the phenomenon responsible for it and explain the observation.
Solution: The phenomenon is called as resonance. When the frequency of the air column becomes equal to the frequency of the tunning fork it air column comes in resonance with the frequency of the tunning fork and produced loud audible sound.
Question: 29
In figure A, B, C and D represent the test tubes each of height 20 cm which are filled with water up to heights of 12 cm, 14 cm, 16 cm and 18 cm respectively. If a vibrating tuning fork is placed over the mouth of test tube D, a loud sound is heard.
(a) Describe the observations with the tubes A, B and C when the vibrating tuning fork is placed over the mouth of these tubes.
(b) Give the reason for your observation in each tube.
(c) State the principle illustrated by the above experiment.
Solution:
(a) Loud sound is heart in test tube B and no sound is heard from test tube A and C.
(b) Reason behind that is resonance. Resonance occurs because frequency of air column in B is same as the frequency of the air column in D. The length of the air column in test tube D is 2cm and the length in test tube B is 6 cm three times to test tube D. the frequencies of vibration of air column in test A and C does not match with frequency of air column in test tube B.
(c) Resonance to occur the frequency of the air column must be equal to the frequency of the tunning fork.
Question: 30
When a troop crosses a suspension bridge, the soldiers are asked to break their steps. Why?
Solution: When soldiers march the force they apply is in the same phase and certain frequency produced by them. If the natural frequency of the suspension bridge is equal to the frequency applied by the soldiers then the bridge might come in resonance and vibrate with high amplitude and collapse. Hence, the soldiers are asked to break their steps while crossing suspension bridge.
Question: 31
Why are the stringed instruments like guitar provided with a hollow sound box?
Solution: The sound box has a air column and the sound box is designed in such a way that natural frequency is same as the string attached to it. Hence, due to resonance the sound box produces loud sound.
Question: 32
How do you tune your radio set to a particular station? Name the phenomenon involved in doing so and define it.
Solution: to tune the radio we have adjust the electrical component of the radio in such a way that the natural frequency of the radio must be equal to the frequency we want the radio to tune into.
The phenomenon used here is called as resonance. As the natural frequency of an object becomes equal to the applied frequency the body comes in the resonance with that frequency.
Multiple Choice Type:
Question: 1
A wire stretched between two fixed supports, is plucked exactly in the middle and then released. It executes (neglect the resistance of the medium):
(a) Resonant vibrations
(b) natural vibrations
(c) Damped vibrations
(d) Forced vibrations
Solution: (b) natural vibrations.
Question: 2
When a body vibrates under a periodic force, the vibrations of the body are:
(a) Natural vibrations
(b) Damped vibrations
(c) Forced vibration
(d) Resonant vibrations
Solution: (c) Forced vibration
Exercise 7 (c)
Question: 1
Name three characteristics of a musical sound.
Solution: loudness, pitch and quality are three characteristic of musical sound.
Question: 2
(a) Which of the following quantity determines the loudness of a sound wave?
(i) Wavelength
(ii) frequency and
(iii) amplitude
(b) How is loudness related to the quantity mentioned above in part (a)?
Solution:
(a) Amplitude of the sound determines the loudness of the sound.
(b) The loudness is proportional to the square of the amplitude.
Question: 3
If the amplitude of a wave is doubled, what will be the effect on its loudness?
Solution: As the loudness is the proportional to the square of the amplitude. Hence, when amplitude is doubled the loudness is increased by 4 times.
Question: 4
Two waves of the same pitch have amplitudes in the ratio 1:3. What will be the ratio of their (i) loudness and (ii) frequencies?
Solution:
(i) As the loudness is the proportional to the square of the amplitude.
Ratio of amplitude = 1:9
(ii) If the pitch is same then frequency is also unchanged.
Ratio of frequency = 1:1
Question: 5
How does the wave pattern of a loud note differ from that of a soft note? Draw a diagram.
Solution: amplitude of loud note is greater than the amplitude of soft note
Waves of soft note and loud note are given below
Question: 6
Name the unit in which the loudness of sound is measured?
Solution: loudness of the sound is measured in units as decibels.
Question: 7
Why is the loudness of the sound heard by a plucked wire increased when it is mounted on a sound board?
Solution: soundboard provides large surface and volume of air for vibrations. Hence, loudness of sound heard by plucked wire increased when it is mounted on a sound board.
Question: 8
Define the term intensity of a sound wave. State the unit in which it is measured.
Solution: Intensity of a sound at point of the medium is the amount of energy passing per second normally through area at that point. Unit of intensity of sound wave is watt per square meter.
Question: 9
How is loudness of sound related to the intensity of wave producing it?
Solution: loudness is directly proportional to the log of intensity.
Question: 10
Comment on the statement ‘loudness of sound is of subjective nature, while intensity is of objective nature’
Solution: The loudness is subjective in nature as it depends upon the ability of listener and it can’t be universally constant. And intensity is a measurable quantity is objective.
Question: 11
State three factors which affect the loudness of a sound heard by a listener.
Solution: loudness of sound heard by listener depends on the amplitude of sound, distance of the listener and surface area of vibrating body.
Question: 12
The bells of a temple are big in size. Why?
Solution: The bells in temple are bigger as the it produces sound of less resonant frequency. Hence, sound can travel long distance.
Question: 13
Name the unit used to measure the sound level.
Solution: sound level measured in decibels.
Question: 14
What is the safe limit of sound level in dB for our ears?
Solution: safe limit for our ears is 120 decibels.
Question: 15
What is meant by noise pollution? Name one source of sound causing noise pollution.
Solution: The unwanted loud sounds above 120dB produce disturbance that is called as noise pollution. Loud speakers cause noise pollution.
Question: 16
What determines the pitch of a sound?
Solution: pitch of sound depends upon its frequency.
Question: 17
Name the subjective property of sound related to its frequency.
Solution: Pitch is the subjective property related to sound related to its frequency.
Question: 18
Name and define the characteristic which enables one to distinguish two sounds of the same loudness, but of different frequencies, given by the same instrument.
Solution: Pitch is the characteristic which enables one to distinguish two sounds of same loudness, but of different frequencies given by the same instrument.
Question: 19
Draw a diagram to show the wave pattern of a high pitch note and a low pitch note, but of the same loudness.
Solution:
Low pitch note.
High pitch note.
Question: 20
How is it possible to detect the filling of a bottle under a water tap by hearing the sound at a distance?
Solution: The length of air column is inversely proportional to the frequency of sound produced. Hence, when water is filling inside of bottle the air column decreases hence the frequency of sound increases and then it is possible to detect the filling of water bottle by hearing the sound.
Question: 21
The frequencies of notes given by flute, guitar and trumpet are respectively 400 Hz, 200 Hz and 500 Hz. Which one of these has the highest pitch?
Solution: As frequency is directly related to the pitch of sound. Hence, trumpet has the highest pitch as it has highest frequency.
Question: 22
Complete the following sentences:
(a)The pitch of sound increases, if its frequency _______.
(b) If the amplitude of a sound is halved, its loudness becomes _______.
Solution:
(a) Increases
(b) One- fourth
Question: 23
The diagram below shows three different modes of vibration P, Q and R of the same string of a given length.
(a) Which vibration will produce a louder sound and why?
(b) Which vibration will produce a sound of maximum shrillness (or pitch) and why?
(c) What is the ratio of the wavelength of vibrations P and R?
Solution:
(a) R vibrations will produce larger sound at its amplitude is high.
(b) P has the highest pitch as it has the highest frequency.
(c) The ratio of wavelength of P and R = 1:3.
Question: 24
Name the characteristic which enables one to distinguish the sound of two musical instruments even if they are of the same pitch and same loudness.
Solution: If the loudness and pitch of the both sounds is same then the quality of the sound is used to distinguish between the sounds of two musical instruments.
Question: 25
How does the two sounds of same loudness and same pitch produced by different instruments differ? Draw diagrams to illustrate your answer.
Solution: The waveforms of the waves will differ to the sounds of the same loudness and same pitch produced by different instrument.
Above two diagrams show the waves produced by different instruments which have same amplitude hence same loudness. They have same period hence same pitch but have different waveforms hence differ in sound.
Question: 26
Two identical guitars are played by two persons to give notes of the same loudness and pitch. Will they differ in quality? Give a reason for your answer.
Solution: As the guitars are identical the waves produced by them are identical hence, they will not differ in the quality.
Question: 27
Two musical notes of the same pitch and same loudness are played on two different instruments. Their wave patterns are as shown in the diagram below.
Explain why the wave patterns are different.
Solution: The waveforms is different because of the quality of wave produced by two different objects. The waveform is based on the subsidiary notes produced by the instruments. Change in notes affects the wave patterns.
Question: 28
Which characteristic of sound makes it possible to recognise a person by his voice without seeing him?
Solution: Quality of sound makes it possible to recognise a person by its voice without seeing him.
Question: 29
State the factor that determines
(i) the pitch of a note,
(ii) the loudness of the sound heard, and
(iii) the quality of the note.
Solution:
(i) Frequency
(ii) Amplitude
(iii) Waveform.
Question: 30
Name the characteristic of the sound affected due to a change in its (i) amplitude, (ii) waveform, and (iii) frequency
Solution:
(i) Loudness
(ii) Quality
(iii) Frequency
Question: 31
Sketches I to IV in figure show sound waves, all formed in the same time interval.
Which diagram shows
(i) a note from a musical instrument,
(ii) a soft (or feeble) note,
(iii) a bass (or low frequency) note.
Solution:
(i) Figure (iv)
(ii) Figure (i)
(iii) Figure (ii)
Question: 32
Shows wave patterns of three sounds A, B and C. Name the characteristic of sound which is the same between (i) A and B, (ii) B and C, and (iii) C and A
Solution:
(i) As the amplitude and waveform is same the loudness and the quality of the sound is same for A and B.
(ii) There is no similarity in B and C
(iii) As the frequency is same, A and C has same pitch.
Question: 33
A microphone is connected to the Y-input of a C.R.O. Three different sounds are made in turn in front of the microphone. Their traces (a), (b) and (c) produced on the screen are shown in figure
(i) Which trace is due to the loudest sound? Give the reason for your answer.
(ii) Which trace is due to the sound with the lowest pitch? Explain your answer.
Solution:
(i) The wave with highest amplitude shows the loudest sound, which is figure (b).
(ii) The lowest pitch has lowest frequency, which is figure (a).
Question: 34
In what respect does the wave pattern of noise and music differ? Draw diagrams to explain your answer.
Solution: The wave pattern or wave form differ for noise and music.
Question: 35
State one difference between a musical note and noise.
Solution: Musical note is regular smooth and pleasant to hear on the other hand noise is irregular, discontinued and unpleasant to the ear.
Multiple Choice Type:
Question: 1
By reducing the amplitude of a sound wave, its:
(a) pitch increases
(b) loudness decreases
(c) loudness increases
(d) pitch decreases
Solution: (b) loudness decreases
Question: 2
Two sounds of same loudness and same pitch produced by the two different instruments differ in their,
(a) amplitudes
(b) frequencies
(c) waveforms
(d) all the above
Solution: (c) waveforms
Question: 3
Two sounds A and B are of same amplitudes, same wave forms but of frequencies f and 2f respectively. Then:
(a) B differ in quality from A
(b) B is grave, A is shrill
(c) B is shrill, A is grave
(d) B is louder than A
Solution: (c) B is shrill, A is grave