CBSE Class 9 Physics Sound Worksheet Set A

Read and download free pdf of CBSE Class 9 Physics Sound Worksheet Set A. Students and teachers of Class 9 Physics can get free printable Worksheets for Class 9 Physics in PDF format prepared as per the latest syllabus and examination pattern in your schools. Standard 9 students should practice questions and answers given here for Physics in Grade 9 which will help them to improve your knowledge of all important chapters and its topics. Students should also download free pdf of Class 9 Physics Worksheets prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this academic year and solve important problems provided here with solutions on daily basis to get more score in school exams and tests

Sound Class 9 Physics Worksheet Pdf

Class 9 Physics students should refer to the following printable worksheet in Pdf for Sound in standard 9. This test paper with questions and answers for Grade 9 Physics will be very useful for exams and help you to score good marks

Class 9 Physics Worksheet for Sound

 

CBSE Class 9 Physics Worksheet - Sound

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INTRODUCTION - SOUND

• Sound is a form of energy like heat energy, light energy, potential energy and kinetic energy. It causes a sensation of hearing in our ears. Th
• The SI unit of sound is decibel (dB) representing sound pressure level (SPL). Decibel is a generic term used to represent the ratio of two quantities on a logarithmic scale as follows: dB = 10 log (X1/X2
• Sound cannot be created nor destroyed but can be changed from one form to another. E.g., when we clap, a sound is produced. Here, muscular energy is converted into sound energy. This is in accordance with the law of conservation of energy.
Similarly, in an electric bell, when connected to electricity starts producing sound. Here, again electrical energy is converted into sound energy.

PRODUCTION OF SOUND:

• Sound is produced due to the vibration of objects.
• The motion of materials or objects causes vibration.
• Vibration is a kind of rapid to and fro motion of an object about a central position. It is also referred to as oscillation.
For example, a stretched rubber band when plucked vibrates and produces sound.

Activity to show that vibrating bodies produces sound: - Strike the prongs of a tuning fork on a rubber pad and bring it near the ear. We can hear a sound. If a suspended table tennis ball is touched with the vibrating prong, the ball is pushed away repeatedly. This shows that the prong is vibrating and vibrating objects produces sound.

(A tuning fork is an instrument used in laboratories to perform sound related experiments).

Examples of how certain sounds are produced -
In every musical instrument, there is a vibrating part which produces sound. In case of musical instruments like flute, the air column vibrates to produce sound.

In stringed musical instruments like sitar, veena etc, there is a tightly stretched string which vibrates to produce sound. In humans, sound is produced by the voice box or the Larynx. Vocal cords in the larynx vibrate and produce sound. We hear sound with our ears. When a bird flaps its wings, a sound is produced.

PROPAGATION OF SOUND

• The travelling of sound is called propagation of sound.
• Sound is propagated by the to and fro motion of particles of the medium.
• When an object vibrates, it sets the particles of the medium around it vibrating. Each particle disturbs the particle. Thus, the disturbance is carried from the source to the listener.
• The disturbance produced by the vibrating body travels through the medium but the particles do not move forward themselves.

SOUND NEEDS A MEDIUM TO PROPAGATE:

• A medium is necessary for the propagation of sound waves.
• The matter or substance through which sound is transmitted is called a medium. The medium can be solid, liquid or gas.
• Sound cannot travel in vacuum. A true vacuum refers to the complete absence of matter. Sound waves can travel only through matter. So, sound needs a physical medium in order to travel anywhere.
• Wave that requires medium to propagate is called Mechanical Wave.For example - sound wave. Sound cannot travel in the absence of a medium.

Activity to show that sound needs a material medium for its propagation. Suspend an electric bell in an air tight bell jar. Connect the bell jar to a vacuum pump. If the switch is pressed, we can hear the sound of the bell. If air is pumped out through the vacuum pump, we cannot hear the sound of the bell. This shows that sound needs a medium to travel and sound cannot travel in vacuum

Question and answers based on the above topics :-

Question. How does the sound produced by a vibrating object in a medium reach your ear?
Answer. When an object vibrates, it necessitates the surrounding particles of the medium to vibrate. The particles that are adjacent to vibrating particles are forced to vibrate. Hence the sound produced by a vibrating object in a medium is transferred from particle to particle till it reaches your ear


Question. Explain how sound is produced by your school bell.
Answer. When the school bell is hit with a hammer, it moves forward and backwards producing compression and rarefaction due to vibrations. This is how sound is produced by the school bell.


Question. Why are sound waves called mechanical waves?
Answer. Sound waves require a medium to propagate to interact with the particles present in it. Therefore sound waves are called mechanical waves.


Question. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer. No. Sound waves require a medium to propagate. Due to the absence of atmosphere on the moon and since sound cannot travel in vacuum, I will not be able to hear any sound produced by my friend.


Question. What is sound and how is it produced?
Answer. Sound is produced due to vibrations. When a body vibrates, it forces the adjacent particles of the medium to vibrate. This results in a disturbance in the medium, which travels as waves and reaches the ear. Hence sound is produced.


Question. Describe with the help of a diagram, how compressions and rarefactions are produced in the air near a source of sound.
Answer. When the school bell is hit with a hammer, it moves forward and backwards producing compression and rarefaction due to vibrations. When it moves forward, it creates high pressure in its surrounding area. This high-pressure region is known as compression. When it moves backwards, it creates a low-pressure region in its surrounding. This region is called rarefaction.


Question. Cite an experiment to show that sound needs a material medium for its propagation.
Answer. Take an electric bell and hang it inside an empty bell-jar which is fitted with a vacuum pump (as shown in the figure below). Initially, one can hear the sound of the ringing bell. Now, pump out some air from the bell-jar using the vacuum pump. You will realize that the sound of the ringing bell decreases. If you keep on pumping the air out of the bell-jar, then glass-jar will be devoid of any air after some time. Now try to ring the bell. No sound is heard but you can see bell prong is still vibrating. When there is no air present in the bell jar, a vacuum is produced. Sound cannot travel through vacuum. Therefore, this experiment shows that sound needs a material medium for its propagation.


Question. Why sound wave is called a longitudinal wave?
Answer. The vibration of the medium that travels parallel to the direction of the wave or along in the direction of the wave, is called a longitudinal wave. The direction of particles of the medium vibrates parallel to the direction of the propagation of disturbance. Therefore, a sound wave is called a longitudinal wave.


Frequently Asked Questions on Sound

Question. How does the sound produced by a vibrating object in a medium reach your ear?
Answer. When an object vibrates, it necessitates the surrounding particles of the medium to vibrate. The particles that are adjacent to vibrating particles are forced to vibrate. Hence the sound produced by a vibrating object in a medium is transferred from particle to particle till it reaches your ear.


Question. Explain how sound is produced by your school bell ?
Answer. When the school bell is hit with a hammer, it moves forward and backwards producing compression and rarefaction due to vibrations. This is how sound is produced by the school bell.


Question.Why are sound waves called mechanical waves?
Answer. Sound waves require a medium to propagate to interact with the particles present in it. Therefore sound waves are called mechanical waves.


Question. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer. No. Sound waves require a medium to propagate. Due to the absence of atmosphere on the moon and since sound cannot travel in vacuum, I will not be able to hear any sound produced by my friend


Question. What is sound and how is it produced?
Answer. Sound is produced due to vibrations. When a body vibrates, it forces the adjacent particles of the medium to vibrate. This results in a disturbance in the medium, which travels as waves and reaches the ear. Hence sound is produced.

 

Exam Questions NCERT Class 9 Science Chapter 12 Sound

Question. Where is the density of air higher; at compressions or at rarefactions?
Answer. At the compression the density of air is higher.


Question. Name the quantity that represents the length of one complete wave.
Answer. Wavelength represents the length of one complete wave.


Question. What is relation between time period and frequency?
Answer. Frequency Time period = 1


Question. Name two animals that communicate using infrasound?
Answer. Rhinoceroses and whales communicate using infrasound.


Question. Name the waves used by bats while flying in the dark.
Answer. Bats use ultrasonic waves while flying in the dark.


Question. What is the distance between two consecutive crests in a wave called?
Answer. Wavelength is the distance between two consecutive crests in a wave.


Question. Is the amplitude of a wave the same, as the amplitude of the vibrating body producing the wave?
Answer. Yes, the amplitude of a wave is same, as the amplitude of the vibrating body producing the wave.


Question. What is the range of frequencies associated with :
(a) Infrasound
(b) Ultrasound
Answer. (a) Infrasound : Sound waves between the frequencies 1 to 20 Hz.
(b) Ultrasound : Sound waves of the frequencies above 20,000 Hz.


Question. What is a stethoscope? Name the principle on which a stethoscope works.
Answer. Stethoscope is a medical instrument used for listening sounds produced within the body, chiefly in the heart or lungs. Stethoscope works on the principle of multiple reflection of sound.


Question. How moths of certain families are able to escape captures from bats? What is the range of frequencies associated with :
(a) infrasound?
(b) ultrasound?
Answer. They have very sensitive hearing equipment, that can hear the squeaks (ultrasound) of bat and know when a bat is flying nearby.
(a) Less than 20 Hz.
(b) More than 20,000 Hz.


Question. A person fires a gun standing at a distance of 55 m from a wall. If the speed of sound is 330 ms–1, find the time for an echo to be heard.
Answer. Given d = 55 m, v = 330 ms–1, t = ?
                 2d = v × t
or t = 2d/v== 2×55/330= 0.3

Question. What are wavelength, frequency, time period and amplitude of a sound wave?
Answer. Wavelength : It is the linear distance between two consecutive compressions or two consecutive rarefactions.
Frequency : The number of compressions or rarefactions taken together passing through a point in one second is called frequency.
Time period : It is the time taken by two consecutive compressions or rarefactions to cross a point.
Amplitude : It is the magnitude of maximum displacement of a vibrating particle about its mean position.


Question. The pulse rate of a man is 80 beats in one minute. Calculate its frequency.
Answer. No. of beats per minute = 80
         No. of beats per second = 60 .
                                            = 80 = 1 3
                        So, frequency = 1.3 Hz


Question. What is echo? Explain the conditions that have to be satisfied to hear an echo?
Answer. Reflection of sound wave from a large obstacle is called an echo. The most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound is off and the obstacle is at least at a distance of 17 m.


Question. Explain, why can echoes not be heard in a small room?
Answer. For hearing echo, there should be at least a distance of 17 m between the source of sound and the body from which sound is reflected. In small rooms this is not the case, hence, echoes are not heard.


Question. Which wave property determines :
(i) loudness (ii) pitch
Answer. (i) The amplitude of the wave determines the loudness. More the amplitude of a wave, more is the loudness produced.
(ii) The pitch is determined by the frequency of the wave. Higher the frequency of a wave, more is its pitch and shriller is the sound.


Question. When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production
remains the same. Do you hear echo sound on a hotter day?
Answer. If the temperature rises, the speed of sound will increase. This in turn will increase the minimum distance required for hearing an echo. No echo is heard because the distance between the source of sound and reflecting body does not increase.


Question. Distinguish between transverse and longitudinal waves (three points).
Answer. Transverse waves :
(i) Particles the medium vibrate at right angles.
(ii) Alternate crests and troughs formed.
(iii) e.g., water waves.

Longitudinal waves :
(i) Particles vibrate parallel to the direction of waves.
(ii) Alternate compressions, rarefaction formed.
(iii) e.g., sound waves.


Question. Does sound follow the same laws of reflection as light does? Explain.
Answer. Yes, sound and light follow the same laws of reflection that are given below :
(a) Angle of incidence at the point of incidence =Angle of reflection. ^+i = +rh
(b) At the point of incidence, the incident sound wave, the normal and the reflected sound wave lie in the same plane.


Question. What is a trough?
Answer. A trough is a depression in a wave, i.e., maximum displacement in the negative direction (below the mean position).


Question. What do you understand by the term infrasonic vibrations?
Answer. The sounds of frequency lower than 20 Hz are called the infrasonics or subsonics.


Question. What is the reflection of sound?
Answer. When sound travels in a given medium, it strikes the surface of another medium and bounces back in some other direction, this phenomenon is called the reflection of sound. The waves are called the incident and reflected sound waves.


Question. What type of surfaces are the best for reflecting sound?
Answer. The best surface for the reflection of sound is polished or rough and big obstacle is necessary.


Question. What are good and bad reflectors of sound?
Answer. Good reflectors means which reflect the sound clearly. Bad reflectors means which do not reflect the sound clearly.


Question. A baby recognizes her mother by her voice. Name the characteristic of sound involved
Answer. The characteristic of sound involved in uniqueness of the sound is quality of sound or timber.


Question. What is SONAR? For what it is used?
Answer. SONAR is Sound Navigation And Ranging. It is a technique used to measure the depth of the sea, locate the sunken ships or icebergs and submarines.


Question. In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer. Sound travels faster in solids when compared to any other medium. Therefore, at a particular temperature, sound travels fastest in iron and slowest in gas.


Question. Does sound follow the same laws of reflection as light does? Explain.
Answer. Yes. Sound follows the same laws of reflection as light. The reflected sound wave and the incident sound wave make an equal angle with the normal to the surface at the point of incidence. Also, the reflected sound wave, the normal to the point of incidence, and the incident sound wave all lie in the same plane.


Question. Give two practical applications of reflection of sound waves.
Answer. (i) Reflection of sound is used to measure the speed and distance of underwater objects. This method is called SONAR. (ii) Working of a stethoscope – the sound of patient’s heartbeat reaches the doctor’s ear through multiple reflections of sound.


Question. Flash and thunder are produced are produced simultaneously, but why the flash is seen first and then the sound is heard?
Answer. This is because the speed of sound in air is very less than the speed of light in air. With the increase in Density of the medium, the speed of sound also increases.


Question. A bucket kept under a running tap is getting filled with water. A person sitting at a distance is able to get an idea when the bucket is about to be filled. (i) What change takes place in the sound to give this idea? (ii) What causes the change in the sound?
Answer. (i) The frequency of sound to increases (f∝l1)when the length (l) of the air column is decreased, i.e., when the bucket is getting filled with water. (ii) Change in sound is caused because air column is decreased on the filling the water in bucket.


Question. How noise and music can change your mood/ mental happiness?
Answer. Music can relax the mind, energize the body, and even help people better manage pain. Whereas noise will put a negative effect on it .


Question. Define the following characteristics of a sound wave
a. Loudness b. Pitch. C. Quality of sound
Answer. A. Loudness: Loudness of sound depends upon the intensity of sound. It is found that. i.e. greater the amplitude, greater will be the intensity and so louder will be the sound. The Unit of loudness is decibels (dB) and The loudness of normal talks is about 60 dB.
B. Pitch: Pitch is the characteristic of a wave by which sound wave appears shrill or grave. It depends upon the frequency of the wave. Higher the frequency higher will be the pitch and vice-versa.
C. Quality : It is the sensation received by the ear by which, we are able to differentiate two sounds (even if they are of same pitch and loudness).

 

More Questions

1. What is sound?
2. with the help of an activity show that vibrating objects produce sound.
3. How does sound propagate in a medium?
4. Why are sound waves called as mechanical wave?
5. Propagation of sound can be visualized as propagation of density variations or pressure variations in the medium. Comment.
6. Sound cannot travel through vacuum, demonstrate by an experiment.
7. With the help of an activity show that SOUND WAVES ARE LONGITUDINAL

WAVES

8. Light is a transverse wave but it is not a mechanical wave. Why?
9. Differentiate between longitudinal and transverse wave.
10. How can we describe a sound wave?
11. Diagrammatically represent that Sound propagates as density or pressure variations
12. Show the sound wave in graphic form
13. A violin and a flute may both be played at the same time in an orchestra. Both sounds travel through the same medium, that is, air and arrive at our ear at the same time. Both sounds travel at the same speed irrespective of the source. But the sounds we receive are different. List the characteristics of sound which make them different from each other. On what factors do they depend.
14. How is a high pitched sound different from a low pitched sound. Support your answer graphically.

 

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