Sound ICSE Class-10 Concise Physics Solutions Selina Publishers Chapter-7. We Provide Step by Step Answer of Exercise-7(A), MCQs-7(A), Numericals -7(A), Exercise-7(B), MCQ-7(B), Exercise-7(C), MCQ-7(C) and Numericals -7(C) Questions of Exercise-7 Sound ICSE Class-10 Concise Class-10 . Visit official Website CISCE for detail information about ICSE Board Class-10.
| Board | ICSE |
| Publications | Selina Publication |
| Subject | Physics |
| Class | 10th |
| Chapter-7 | Sound |
| Book Name | Concise |
| Topics | Solution of Exercise-7(A), MCQs-7(A), Numericals -7(A), Exercise-7(B), MCQ-7(B), Exercise-7(C), MCQ-7(C) and Numericals -7(C) |
| Academic Session | 2021-2022 |
Sound ICSE Class-10 Concise Physics Solutions Selina Publishers Chapter-7
-: Select Exercise :-
Exercise-7(A), MCQs-7(A), Numericals -7(A),
Exercise-7(B), MCQ-7(B), Exercise-7(C), MCQ-7(C) and Numericals -7(C)
How to Solve Numericals of Sound ICSE Class-10
Note :- Read all the Chapter-7 Sound to clear concept of Sound topic carefully and solve All the example given in your ICSE text book with Numericals before starting Solution of Chapter – 7 “Sound” exercise. Do not forget Keyword during Solution.
Selina Physics Solutions “Sound” Exe- 7 (A)
Page 154
Question 1
What are mechanical waves?
Answer 1
Mechanical waves are the waves which require material medium to transfer energy.
Question 2
Define the following terms in relation to a wave: (a) amplitude (b) frequency (c) wavelength (d) wave velocity
Answer 2
(a)Amplitude: The maximum displacement of the particle of medium on either side of its mean position is called the amplitude of wave. Its S.I. unit is metre (m).
(b) Frequency: The number of vibrations made by a particle of the medium in one second is called the frequency of the waves.
It is also defined as the number of waves passing through a point in one second. Its S.I. unit is hertz (Hz).
(c) Wavelength: The distance travelled by the wave in one time period of vibration of particle of medium is called its wavelength. Its S.I. unit is metre (m).
(d) Wave velocity: The distance travelled by a wave in one second is called its wave velocity. Its S.I. unit is metre per second (ms-1).v
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
Answer 3
(i) Wavelength (or speed) of the wave changes, when it passes from one medium to another medium.
(ii) Frequency of a wave does not change when it passes from one medium to another medium.
Question 4 (Sound ICSE Class-10 Concise Selina)
State two factors on which the speed of a wave travelling in a medium depends?
Answer 4
Two factors on which the speed of a wave travelling in a medium depends are:
(i) Density: The speed of sound is inversely proportional to the square root of density of the gas.
(ii) Temperature: The speed of sound increases with the increase in temperature.
Question 5
State two differences between the light and sound waves.
Answer 5
1)The light waves can travel in vacuum while sound waves need a material medium for propagation.
2)The light waves are electromagnetic waves while sound waves are the mechanical 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 sound wave is used.
Answer 6
(i) Just as rays of light, sound waves travel back in the opposite direction on hitting an obstacle.
(ii) This is called the reflection of sound.
(iii) The laws of reflection for sound are the same as those for light.
(iv) Repetition of sound caused by reflection of sound waves from an obstacle is known as an echo.
(v) A hearing aid is one such device used by people who are hard of hearing. Here, sound waves, which are received by the hearing aid, are reflected into a narrower area leading to the ear.
Question 7
What is meant by an echo? State two conditions necessary for an echo to be heard distinctly?
Answer 7
If a person stands at some distance from a wall or a hillside and produces a sharp sound, he hears two distinct sounds: one is original sound heard almost instantaneously and the other one is heard after reflection from the wall or hillside, which is called echo.
The condition for the echo: An echo is heard only if the distance between the person producing the sound and the rigid obstacle is long enough to allow the reflected sound to reach the person at least 0.1 second after the original sound is heard.
Question 8 (Sound ICSE Class-10 Concise Selina)
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.
Answer 8
t = 2d/V = 2 x 12/340 = 24/340 < 0.1 seconds so the man will not be able to hear the echo. This is because the sensation of sound persists in our ears for about 0.1 second after the exciting stimulus ceases to act.
Question 9
State two applications of echo.
Answer 9
The applications of echo:
1)Dolphins detect their enemy and obstacles by emitting the ultrasonic waves and hearing their echo.
2)In medical science, the echo method of ultrasonic waves is used for imaging the human organs such as the liver, gall bladder, uterus, womb etc. This is called ultrasonography.
Question 10
Explain how the speed of sound can be determined by the method of echo?
Answer 10
Sound is produced from a place at a known distance say, d at least 50 m from the reflecting surface. The time interval t in which the echo reaches the place from where the sound was produced, is noted by a stop watch having the least count 0.01 s. then the speed of sound is calculated by using the following relation
V = total distance travelled / time interval = 
m/s
Question 11
State the use of echo by a bat, dolphin and fisherman.
Answer 11
Bats, dolphin and fisherman detect their enemies or obstacles or position of fish by emitting/sending the ultrasonic waves and hearing/detecting the echo.
Question 12
How do bats avoid obstacles in their way, when in flight?
Answer 12
Bats can produce and detect the sound of very high frequency up to about 1000kHz. The sounds produced by flying bats get reflected back from any obstacle in front of it. By hearing the echoes, bats come to know even in the dark where the obstacles are. So they can fly safely without colliding with the obstacles.
Question 13
What is meant by sound ranging? Give one use of sound ranging.
Answer 13
The process of detecting obstacles with the help of echo is called sound ranging. It’s used by the animals like bats, dolphin to detect their enemies.
Question 14 (Sound ICSE Class-10 Concise Selina)
Name the waves used for sound ranging. State one reason for their use. Why are the waves mentioned by you, not audible to us?
Answer 14
The ultrasonic waves are used for the sound ranging. Ultrasonic waves have a frequency more than 20,000 Hz but the range of audibility of human ear is 20Hz to 20,000 Hz
Question 15
What is SONAR ? State the principle on which it is based.
Answer 15
Sonar is sound navigation and ranging. Ultrasonic waves are sent in all directions from the ship and they are received on their return after reflection from the obstacles. They use the method of echo.
Question 16
State the use of echo in medical field.
Answer 16
In medical science, echo method of ultrasonic waves is used for the imaging of human organs such as liver, gall bladder, uterus, womb; which is called ultra sonography.
Concise Physics Solutions “Sound” MCQ – 7 (A) Selina Publishers
Page 154
Question 1
The minimum distance between the source and the reflector in air, so that an echo is heard is approximately equal to:
(a) 10 m
(b) 17 m
(c) 34 m
(d) 50 m
Answer 1
(b) 17 m
Explanation: An echo is heard distinctly if it reaches the ear at least 0.1 s after the original sound.
If d is the distance between the observer and the obstacle and V is the speed of sound, then the total distance travelled by the sound to reach the obstacle and then to come back is 2d and the time taken is,
t = Total distance travelled/Speed of sound = 2d/V
or, d = V t/2
Putting t = 0.1 s and V = 340 m/s in air at ordinary temperature, we get:
d = (340 x 0.1)/2 = 17 m
Thus, to hear an echo distinctly, the minimum distance between the source and the reflector in air is 17 m.
Question 2
To detect the obstacles in their path, bats produce:
(a) Infrasonic waves
(b) Ultrasonic waves
(c) Electromagnetic waves
(d) Radio waves
Answer 2
(b) Ultrasonic waves
Numericals -7(A) Sound ICSE Class-10 for Selina Publishers
Page 154
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.
Answer 1
(i)Frequency or the number of waves produced per second
= Velocity/Wavelength
= 24 / 20 x 10-2
=120
(ii)Time = 1/ frequency = 1/ 120= 8.3 x 10-3 seconds
Question 2 (Sound ICSE Class-10 Concise Selina)
Calculate the minimum distance in air required between the source of sound and the obstacle to hear an echo. Take the speed of sound in air = 350m s-1
Answer 2
Velocity = 2D/Time
350 = 2 x D/ 0.1
D =350 x 0.1 / 2 = 17.5 m
Page 155
Question 3
What should be the minimum distance between the source and reflector in water so that echo is heard distinctly? (The speed of sound in water = 1400m/s)
Answer 3
Velocity = 2D/Time
1400 = 2 x D/ 0.1
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 350m/s-1. (b) Will the man be able to hear a distinct echo? Explain the answer.
Answer 4
(a)Velocity = 2D/Time
Time = 2 x 25 / 350 =0.143 seconds
(b)Yes, because the reflected sound reaches the man 0.1 second after the original sound is heard and the original sound persists only for 0.1 second.
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?
Answer 5
Thus, after 0.002 s, the signal is received back after reflecting from the aeroplane.
Question 6 (Sound ICSE Class-10 Concise Selina)
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).
Answer 6
Velocity = 2 x D/Time
Time after which an echo is heard = 2 D/Velocity = 2 x 48 / 320 = 0.3 seconds
Question 7
A ship on the surface of water sends a signal and receives it back from the submarine inside water after 4s. Calculate the distance of submarine from the ship. (The speed of sound in water is 1450m/s-1).
Answer 7
2 D = velocity x time
D = (velocity x time) / 2 = 1450 x 4 / 2 = 2900 m = 2.9 km
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.
Answer 8
5 vibrations by pendulum in 1 sec
So8 vibrations in 8/5 seconds = 1.6 sec
Velocity = 2 x D/ time
340 = 2 x D/ 1.6
D = 340 x 1.6 / 2 = 272 m
Question 9
A person standing between two vertical cliffs produces the sound. Two successive echoes are heard at 4s and 6s. Calculate the distance between the cliffs. (Speed of sound in air = 320m/s)
Answer 9
The distance of first cliff from the person, 2 x D1 = velocity x time
D1 = 320 x 4 / 2 = 640 m
Distance of the second cliff from the person, D2 = 320 x 6 / 2 = 960 m
Distance between cliffs = D1 + D2 = 640 + 960 = 1600 m
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 shots after 2s and 3s respectively. Calculate x and y(take speed of sound 320m/s)
Answer 10
The person B hears two of the fired shots , the first one is direct from the gun while other sound comes after reflection from the cliff
Speed of sound 320m/s
Time taken by the sound to reach from A to B directly
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 1.5s. If the velocity of wave in sea water is 1400m/s, find the depth of sea.
Answer 11
Depth of the sea = velocity x time/2 = 1400 x 1.5 / 2 = 1050 m
Question 12 (Sound ICSE Class-10 Concise Selina)
Figure below shows the distance-displacement graph of two waves A and B. Compare (i) the amplitude, (ii) the wavelength of the two waves.
Answer 12
Amplitude is the maximum displacement from the mean position. For A the maximum displacement = 10cm and for B the maximum displacement = 5cm.
The ratio of maximum amplitude is 
Wavelength of A=8cm
Wavelength of B=16cm
The ratio of wavelength is 
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Q no 10 in 7(b) is written as question no 14.
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