NCERT Exemplar Class 9 Science Solutions Chapter 12 Sound
Have you ever wondered why we hear echoes, why drums are so loud or how musical instruments form rhythm? Chapter 12- Sound of NCERT Class 9 Science is the simplest possible explanation of these interesting concepts. In this chapter, you will find out how sound is carried over various media, how we can hear things with different tones due to the sound waves, and how sound waves determine the loudness and the pitch of sound.
This Story also Contains
- NCERT Exemplar Class 9 Science Solutions Chapter 12 - MCQ
- NCERT Exemplar Class 9 Science Solutions Chapter 12 - Short Answer
- NCERT Exemplar Class 9 Science Solutions Chapter 12-Long Answer
- NCERT Exemplar Class 9 Science Solutions Chapter 12 – Important Concepts and Formulas
- Advantages of NCERT Exemplar Class 9 Science Chapter 12 Sound
- The Sound Class 9 NCERT Exemplar, Sound solutions have a very clear, structured explanation that aids students to learn complex concepts such as wave motion, frequency, amplitude and pitch. With such masterfully developed responses, students become confident and precise in preparing for examinations. Solution is also helpful in enhancing conceptual clarity, and thus the revision is quick and intelligent.
- NCERT Class 9 Science Exemplar Solutions for Other Chapters
The NCERT Exemplar Class 9 Science Solutions Chapter 12 Sound gives good and precise answers to all the significant questions. These step-by-step responses enhance conceptual knowledge among the students, and are most handy in examinations. These Class 9 Sound solutions were designed by experts to make the learning process enjoyable for the students by breaking down complex concepts into simple steps that are easy to learn. These selected exemplar solutions have all the major concepts that you can study, whether you are preparing for CBSE Class 9 exams or competitive exams such as JEE and NEET in future. These NCERT Exemplar Solutions assist students in becoming better at solving problems, comprehending numerical problems, and studying within a short period before exams. Moreover, these NCERT Exemplar Class 9 Solutions Science Chapter 12 Sound provide solved MCQs, short answers, and long questions so that students can practice in detail and increase their accuracy. They form one of the most effective learning tools in the construction of a solid background on the significant subject of sound and its properties.
NCERT Exemplar Class 9 Science Solutions Chapter 12 - MCQ
The Multiple Choice Questions (MCQs) of NCERT Exemplar Class 9 Science Chapter 12 can be utilised to revise significant concepts among students in a fast and effective manner. These NCERT Exemplar Class 9 Science Solutions Chapter 12 enhance the conceptual knowledge and enhance test accuracy during school tests and also during competitive examinations.
Question:1
Note is a sound
(a) of mixture of several frequencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) Always unpleasant to listen
Solution:
The sound of a single frequency is called a tone.
The sound of a mixture of multiple frequencies is called a note.
This mixture may have more than two frequencies.
The frequency of sound is also known as pitch.
Frequency depends on the structure of a sound-producing device.
That is why it is said that frequency depends on the source of the sound.
The correct answer to this question is A.
Question:2
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Solution:
The frequency of sound depends on the mechanical structure of the sound-producing device.
Different keys of the piano will produce sounds of different frequencies. A single key will always produce a sound of the same frequency. If we strike the key with force, the frequency will not change, but the amplitude of sound will change, and it will lead to a change in loudness.
Frequency is also known as pitch, so we can say that if we strike harder, the sound will be louder, but the pitch will be the same.
Hence, the correct option is option A
Question:3
In SONAR, we use
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves
(d) audible sound waves
Solution:
Sonar is the navigation technique used to navigate the location of submarines underwater, and it uses Ultrasonic waves.
Question:4
Sound travels in the air if
(a) Particles of medium travel from one place to another
(b) There is no moisture in the atmosphere
(c) Disturbance moves
(d) Both particles as well as disturbance travel from one place to another.
Answer: c
Solution:When sound travels in a medium, molecules of the medium do not go from one place to another.
The disturbance due to sound is transferred from one molecule to another, hence we can say disturbance travels when sound travels.
In the presence of moisture, the speed of sound in air increases. Therefore, sound can certainly travel in a moist atmosphere.
Hence, the correct answer to this question is option C
Question:5
When we change feeble sound to loud sound we increase its
(a) frequency
(b) amplitude
(c) velocity
(d) wavelength
Answer: b
Solution:Generally, sound is characterised by its pitch and loudness.
Pitch is the frequency of sound, which tells us the number of oscillations, any particle will make in one second.
$f=\frac{1}{T}$
The loudness represents the energy or intensity of the sound.
It is generally governed by the fact of how far a particle moves in its oscillation.
This maximum displacement of the particle in oscillation is called amplitude.
So, loudness increases mean amplitude of oscillation increases.
Hence, the correct answer to this question is option B
Question:6
In the curve (Fig.12.1) half the wavelength is
(a) A B
(b) B D
(c) D E
(d) A E
Answer: b
Solution:The distance between two consecutive crests or consecutive troughs is equal to the wavelength of any sound.
In the given figure, the separation between A and E will be equal to one wavelength.
Therefore, half a wavelength will be equal to the AC or CE or BD distance.
Hence, the correct answer to this question is option B
Question:7
Earthquake produces which kind of sound before the main shock wave begins
(a) ultrasound
(b) infrasound
(c) audible sound
(d) none of the above
Answer: b
Solution:An earthquake produces Seismic waves before the main shock wave.
The Seismic waves have a frequency less than 10 Hz.
This frequency is less than the audible range, and it is called infrasound or infrasonic wave.
The sound frequency more than that of the audible range is called ultrasound or ultrasonic waves.
Sound of frequency less than 20 Hz is called infrasonic, and a frequency more than 20,000 Hz is called ultrasonic.
The correct answer to this question is option B
Question:8
Infra sound can be heard by
(a) dog
(b) bat
(c) rhinoceros
(d) human beings
Solution:
The frequency range that human beings can hear is called audible sound.
Sound of frequency less than 20 Hz is called infrasonic, and a frequency more than 20,000 Hz is called ultrasonic.
Rhinoceroses can sense sounds of frequencies less than the audible range, which is called infrasound.
The correct answer to this question is option C.
Question:9
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting:
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other musical instruments
(d) loudness of sound
Solution:
The frequency of sound generated from the string depends on the length of the string, the tension in the string, as well as thickness of the string.
Hence, by adjusting the strings of the sitar, the Sitarist adjusts the frequency with other musical instruments.
Loudness, intensity or amplitude all represent the same physical phenomenon, and it depends on how hard you strike the string.
Hence, the correct option is option C
NCERT Exemplar Class 9 Science Solutions Chapter 12 - Short Answer
The NCERT Exemplar Class 9 Science Chapter 12 short answer questions enable the students to form clarity with concepts such as sound propagation, sound amplitude, sound frequency, sound pitch, and sound resonance. These brief questions are effective in analytical skills and strengthening exam preparation. The solutions enable the students to come up with precise and accurate answers as expected in the CBSE exams.
Question:10
Answer:
In the propagation of sound, the particle of the medium oscillates.By the graph, we can see that a time period of one complete oscillation is 2 microseconds.
The wavelength of a disturbance is defined as the distance travelled by the disturbance in one time period of oscillation.
$\lambda=V\times T$
or
$\lambda=\frac{V}{f}$
As the disturbance is moving with 1500 m/s and the time period is 2 microseconds, the wavelength can be calculated as:
$\lambda=V\times T =1500 \times 2 \times 10^{-6}=3 \times 10^{-3}=3mm$
Question:11
Answer:
The difference between a human male voice and a female voice is based on the basis of pitch or frequency.The male voice will have a lower frequency in comparison with the female voice.
We know that frequency is the inverse of the time period of oscillation.
$f=\frac{1}{T}$
In the given graph, it is quite visible that the time period of graph (a) is more than the time period of graph (b).
Therefore, graph (a) must correspond to a male voice.
Question:12
Answer:
When we observe a sound directly or after reflection from any building, we call it an echo.This echo can be heard, or these two sounds can be distinguished, only if the time gap between them is more than 0.1 seconds.
For this, the separation between the source and the wall must be more than 16 meters.
Assuming speed of sound = 320m/s
The distance between the source and the wall is d, then the time to reach the reflected sound will be:
$t=\frac{2d}{V}$
In the given case, the size of the park is small. Therefore, it cannot cause any echo of the sound produced on the road.
Question:13
Answer:
The human ear can sense sound only if its frequency is more than 20 Hz and less than 20,000 Hz.Sound of frequency less than 20 Hz is called infrasonic, and a frequency more than 20,000 Hz is called ultrasonic.
The frequency of the disturbance created by the humming bee is more than 20 Hz, which is why we can hear the sound.
Due to the vibration of the pendulum, the frequency of disturbance is less than 20 Hz, and we cannot hear the sound of the vibration of the pendulum.
Question:14
Answer:
A transverse wave cannot travel in air or within water.A transverse wave can only travel at the surface of water or in solids.
So when any explosion takes place at the bottom of a lake, the shock waves have to travel within the water.
These shock waves cannot be transverse, and they have to be longitudinal waves like a sound wave.
Question:15
Answer:
The speed of light is very large in comparison with the speed of sound.We can assume that lightning can be seen, without any time delay, as light travels very fast.
If the sound produced by a thunderstorm is heard 10 seconds after lightning, that means the sound took 10 seconds to reach from the thundercloud.
As the speed of sound is 340 m/s, so distance travelled by sound in 10 seconds will be 3400 meters.
So the approximate distance of the thundercloud is 3.4 km.
Question:16
For hearing the loudest ticking sound heard by the ear, find the angle x in the Fig.12.4.
Answer:
Similar to light, sound also follows the law of reflection.If I sound is coming at an incident angle of $\angle i$, then it will go at the same reflection angle $\angle i=\angle r$.
In the given question, the sound coming through the first pipe has an angle of incidence equal to 40°, which can be calculated as (90° - 50°)
The same sound will be reflected at an angle of 40°. Therefore, the second pipe has to be kept at an angle of 40° from normal.
Therefore, the value of x will be 40°.
Question:17
Why is the ceiling and wall behind the stage of good conference halls or concert halls made curved?
Answer:
The design of the ceiling and walls in a good conference hall is to ensure proper sound at every seat in the conference hall.This design is called acoustic design, and design engineers are called acoustic engineers.
The ceiling and wall behind the stage are made curved, so that the reflected sound from them can reach the audience evenly.
NCERT Exemplar Class 9 Science Solutions Chapter 12-Long Answer
Sound Class 9 NCERT Exemplar long answer questions assist the students in describing the specifics of sound propagation, the nature of sound waves, and their use in real life. These are questions that need reasoning, step-by-step explanation and a proper interpretation of formulas. A comprehensive solution to these enhances conceptual clarity and enhances skills in exam writing.
Question:18
Represent graphically by two separate diagrams in each case
(a) Two sound waves having the same amplitude but different frequencies?
(b) Two sound waves having the same frequency but different amplitudes.
(c) Two sound waves having different amplitudes and also different wavelengths.
Answer:
In the propagation of sound, the particle of the medium oscillates.The time to complete one oscillation is called the time period T.
Pitch is the frequency of sound, which tells us the number of oscillations any particle will make in one second.
$f=\frac{1}{T}$
The distance between two consecutive crests or troughs is equal to the wavelength of any sound.
By this information, we can draw the corresponding graphs.
Question:19
Establish the relationship between speed of sound, its wavelength and frequency. If velocity of sound in air is 340 m s–1, calculate
(i) Wavelength when frequency is 256 Hz.
(ii) Frequency when the wavelength is 0.85 m.
Answer:
The wavelength of any sound is defined as the distance travelled by the disturbance in one time period of the oscillation of a particle.$\lambda=V \times T$
The number of oscillations per unit time is called frequency. Hence, frequency and time period are related as.
$f=\frac{1}{T}$
By putting the value of the time period in relation to wavelength, we will get:
$\lambda =\frac{V}{f}\Rightarrow V=f \times \lambda$
i) If frequency and sound velocity are given, wavelength can be calculated as:
$\lambda =\frac{V}{f}\\ \Rightarrow \lambda =\frac{340}{256}=1.328125m$
ii) If wavelength and sound velocity are given, the frequency of sound can be calculated as:
$f=\frac{V}{\lambda }\\ \Rightarrow f =\frac{340}{0.85}=400Hz$
Question:20
Answer:
In the propagation of sound, the particles of the medium oscillate.The time to complete one oscillation is called the time period T.
Pitch is the frequency of sound, which tells us the number of oscillations any particle will make in one second.
$f=\frac{1}{T}$
The distance between two consecutive crests or troughs is equal to the wavelength of any sound.
NCERT Exemplar Class 9 Science Solutions Chapter 12 – Important Concepts and Formulas
Sound Class 9 NCERT Exempla describes the principles of the science of sound, its travelling, and the way to measure its characteristics. The NCERT exemplar has significant conceptual questions and solved examples to facilitate the learning of these concepts by students. Knowledge of major formulas and concepts will assist in working to ease the numerical problems and to work better in exams. These formulas are very convenient for revision and frequent access.
1. Sound Production:
Sound is produced due to the vibration of objects. These vibrations create disturbances in particles of the medium.
2. Propagation of Sound:
Sound travels through a medium (solid, liquid, or gas) in the form of longitudinal waves.
3. Speed of Sound Formula:
Speed of Sound $(v)=\frac{\text { Distance travelled }}{\text { Time taken }}$
4. Relation between Speed, Wavelength, and Frequency:
$
v=\lambda \times f
$
where,
$\boldsymbol{v}=$ speed of sound
$\lambda=$ wavelength
$f=$ frequency
5. Frequency Formula:
$\begin{aligned}
&f=\frac{\mathbf{1}}{T}\\
&\text { where, } T=\text { time period of vibration. }
\end{aligned}$
6. Loudness:
Loudness depends on the amplitude of the sound wave. Higher amplitude means louder sound.
7. Pitch:
Pitch depends on frequency. Higher frequency means higher pitch.
8. Echo:
An echo is the reflection of sound heard after 0.1 seconds or more.
9. Distance Formula for Echo:
Distance $=\frac{v \times t}{2}$
10. Range of Hearing:
Humans can hear sounds between 20 Hz and 20,000 Hz.
11. Audible Frequency Range:
Anything below 20 Hz is infrasonic, and anything above 20 kHz is ultrasonic.
Advantages of NCERT Exemplar Class 9 Science Chapter 12 Sound
The Sound Class 9 NCERT Exemplar, Sound solutions have a very clear, structured explanation that aids students to learn complex concepts such as wave motion, frequency, amplitude and pitch. With such masterfully developed responses, students become confident and precise in preparing for examinations. Solution is also helpful in enhancing conceptual clarity, and thus the revision is quick and intelligent.
- Assists students in grasping scientific ideas of sound, such as loudness, pitch, frequency, and uses easily.
- Enhances skill in solving problems through providing step-by-step answers to mathematical and theoretical problems.
- Creates a sense of confidence in the exam because students will be used to the format of questions and levels of difficulty.
- It is a good revision tool as it saves time when revising on vital topics prior to exams.
- Enhances accuracy and speed in calculations and conceptual questions through repeated practice.
- Eliminates misunderstandings, ambiguities and confusion and facilitates the learning process.
- Promotes self-guided learning because students do not require external support to assess their learning.
NCERT Class 9 Exemplar Solutions for Other Subjects
NCERT Class 9 Science Exemplar Solutions for Other Chapters
Viewing NCERT Class 9 Science Exemplar Solutions of the other chapters is highly beneficial for students who are going to exams. These solutions provide a chapter-by-chapter solution to facilitate the ease with which students can access explanations, solved questions, MCQs, short answers and long answers all under a single roof. These exemplar links will ensure that the students develop well-placed fundamentals and improve their practice in CBSE Class 9 Science with accurate and clear answers that are structured and well laid out.
|
Chapter-wise solutions |
Check NCERT Solutions for questions given in the book
Check the Solutions of the Questions Given in the Book
| Chapter No. | Chapter Name |
| Chapter 1 | Matter in Our Surroundings |
| Chapter 2 | Is Matter Around Us Pure |
| Chapter 3 | Atoms and Molecules |
| Chapter 4 | Structure of The Atom |
| Chapter 5 | The Fundamental Unit of Life |
| Chapter 6 | Tissues |
| Chapter 7 | Motion |
| Chapter 8 | Force and Laws of Motion |
| Chapter 9 | Gravitation |
| Chapter 10 | Work and Energy |
| Chapter 11 | Sound |
| Chapter 12 | Improvement in Food Resources |
Also, Read NCERT Solution Subject Wise
Check NCERT Notes Subject Wise
Also, check the NCERT Books and NCERT Syllabus here
Frequently Asked Questions (FAQs)
Q: If a person will shout, does that mean the frequency of sound is increased?
A:
No, the frequency of sound produced by any woman does not change on changing the loudness. The intensity of sound increases on shouting but the frequency of sound will remain the same. Frequency is generally known as pitch which can be seen as identification of someone’s voice
Q: Can we talk on the moon?
A:
No, sound needs medium to travel and there is no atmosphere on the moon. Therefore, we cannot talk on the moon as we talk on earth.
Q: Can I revise using these questions?
A:
Yes! These are perfect for quick and smart revision before your tests.
Q: Are these exemplar questions important?
A:
Yes! They help you understand the chapter better and are great for exam practice.
Q: “Frequency is identification of any sound”. comment on the statement.
A:
When sound travels and changes medium, the speed of sound changes. It causes a change in wavelength but not the frequency. Frequency does not depend on the medium.
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