Samacheer Kalvi 9th Science Solutions Chapter 8 Pdf

Samacheer Kalvi 9th Science Solutions Chapter 8 Pdf

Tamilnadu Board Samacheer Kalvi 9th Science Solutions Chapter 8: Tamilnadu State Board Solution Class 9 Science Chapter 8 – SOUND.

Samacheer Kalvi 9th Science Solutions Chapter 8: Overview

Board Samacheer Kalvi
Class 9
Subject Science
Chapter 8
Chapter Name SOUND

Samacheer Kalvi 9th Science Solutions Chapter 8 Pdf

Chapter 8
Sound

Exercise:

I) Choose the correct answer.

1) Which of the following vibrates when a musical note is produced by the cymbals in an orchestra?

a) Stretched strings

b) Stretched membranes

c) Air columns

d) Metal plates

Ans: d) Metal plates

Metal plates vibrates when a musical note is produced by the cymbals in an orchestra.

2) Sound travels in air:

a) If there is no moisture in the atmosphere.

b) If particles of medium travel from one place to another.

c) If both particles as well as disturbance move from one place to another.

d) If disturbance moves.

Ans: d) If disturbance moves.

Because, sound wave is a longitudinal wave which moves due the vibration of particles of air and particles are not displaced from one position to another, only disturbance is moved in the form of compression and rarefactions.

3) A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through

a) Wax

b) Vacuum

c) Water

d) Empty vessel
Ans: b) Vacuum
The normal hearing range of a person is 20 Hz to 20000 Hz. The musical instrument is producing continuous note and it cannot be heard by a person having normal hear range. That means this note is passing through the vacuum. Because, sound wave is longitudinal wave which requires material medium for its propagation and hence through vacuum the person cannot hear note produced.
4) The maximum speed of vibrations which produces audible sound will be in
a) Sea water

b) Ground glass

c) Dry air

d) Human blood

Ans: b) Ground glass

Because, the velocity of sound is maximum in solids than liquid and gases.

5) The sound waves travel faster
a) In liquids

b) In gases

c) In solids

d) In vacuum

Ans: c) In solids

Because, the velocity of sound is maximum in solids than liquids and gases.
And sound waves requires material medium for their propagation so through vacuum it cannot pass.

II. Fill in the blanks.
1) Sound is a ____________ wave and needs a material medium to travel.

Ans: Sound is a longitudinal wave and needs a material medium to travel.

2) Number of vibrations produced in one second is ____________.

Ans: Number of vibrations produced in one second is frequency of wave.

3) The velocity of sound in solid is ____________ than the velocity of sound in air.

Ans: The velocity of sound in solid is greater than the velocity of sound in air.

4) Vibration of object produces _________.

Ans: Vibration of object produces sound waves.

5) Loudness is proportional to the square of the ____________.

Ans: Loudness is proportional to the square of the amplitude.

6) ____________ is a medical instrument used for listening to sounds produced in the body.

Ans: Stethoscope is a medical instrument used for listening to sounds produced in the body.

7) The repeated reflection that results in persistence of sound is called ____________.

Ans: The repeated reflection that results in persistence of sound is calledreverberations.

III. Match the following.
Tuning fork: Production of sound

Sound: Longitudinal wave

Compressions: The point where density of air is maximum

Amplitude: Maximum displacement from the equilibrium position

Ultrasonic: The sound whose frequency is greater than 20,000 Hz

IV. Answer briefly.
1) Through which medium sound travels faster, iron or water? Give reason.
Ans:
The sound travels faster in iron than water.Because, the velocity of sound depends on the elasticity of the medium. Solids are having highest elasticity than liquids and gases.
Therefore, velocity of sound is less in water than iron. Hence, sound travels faster in iron than water.

2) Name the physical quantity whose SI unit is ‘hertz’. Define.
Ans:
The SI unit of frequency is hertz. The number of vibrations produced in one second is called as the frequency of the wave. It is denoted by n. Human ear is audible for sound of frequency 20 Hz to 20000 Hz. The sound with frequency less than 20 Hz is called as infrasonic sound and with frequency greater than 20000 Hz is called as ultrasonic sound. The human ear cannot hear the infrasonic and ultrasonic sound.

3) What is meant by supersonic speed?
Ans: The sound waves are the longitudinal waves which requires material medium for their propagation. The velocity of sound is maximum in solids than liquid and gases.
The speed of sound in air is 330 m/s at 00C and 340 m/s at 250C.
When the speed of any object exceeds the speed of sound in air which is 330 m/s then it is said that it is traveling with supersonic speed.
For example: bullets, jets, aircrafts are traveling with supersonic speed.

4) How does the sound produced by a vibrating object in a medium reach your ears?
Ans: Sound waves are the longitudinal waves which requires material medium for its propagation. The velocity of sound is maximum in solids than liquids and gases.
When an object is set into vibration then the particles of the medium start to vibrate around their mean position. Since, the particles cannot carry the sound directly to the ear. A particle of the medium in close contact with the vibrating object is displaced from its mean position and get collide with its adjacent particle. And exerts a force on that particle and then reach to its mean position again. The second particle which receives the vibrations get displaced from its mean position and in similar way it exerts a force on its adjacent particle and it is again displaced to its original position.
In this way, this process continues till the sound is heard by ear. And it is observed that, only the disturbance created by the sound is traveled through the medium and not the particles of the medium directly. The particles are only vibrating around their mean position only to transfer the disturbance produced. In this way the disturbance passed is called as wave.
In this way the sound produced by a vibrating object in a medium reach our ears.

5) You and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Ans: Sound waves are the longitudinal waves which requires material medium for their propagation. On the moon there is no atmosphere. And hence, sound produced cannot propagated due to the absence of medium for propagation.
Hence, I am not able to hear any sound produced by my friend.

V. Answer in detail.
1) Describe with diagram, how compressions and rarefactions are produced.
Ans:
To understand how compressions and rarefactions are produced, we perform an activity. We take a spring and move it forward and backward. We see that, in some parts the spring is closer and in some parts it is far apart.
In the similar way, light can travels through the medium.
The region where the turns of spring are closer or crowded is called as compressions. And the region where the turns of spring are far apart is called as rarefactions.
These compressions and rarefactions are produced alternately. And if we oscillate the spring then this compressions and rarefactions move along the spring.
The wave which propagates this compressions and rarefactions is called as longitudinal wave.in this wave, particles of the medium vibrate to and fro about their mean position along the direction of propagation of the wave.
Sound waves are also the longitudinal waves, and it is propagated in similar compressions and rarefactions. Compression is the region where particles of the medium crowded and rarefactions is the region where particles are far apart.
Thus sound waves are the longitudinal waves which travels through the medium in the form of compressions and rarefactions which are alternately produced.

2) Verify experimentally the laws reflection of sound.
Ans:
Sound waves are the longitudinal waves which requires material medium for their propagation.
When sound get incident on any object it get also reflected like light waves. The laws of reflection of sound are same as the laws of reflection of light which are as follows:
a) The angle of incidence is equal to the angle of reflection
b) The incident sound wave, the normal and the reflected sound wave lie in the same plane.
Experiment to verify the laws of reflection:
Take a white sheet and fix it on drawing board by pins.
Draw the line PQ to place the metal plate which acts as a reflecting surface for sound waves produced. And draw a normal MN to this line PQ.
Now draw a line MA making angle 400 with normal as shown in fig. and place a metal tube along the line MA. To the end A place a ticking watch.
Now, place the other tube on line MB as shown in fig. and put your ear to its end B to hear the sound reflected from the metal plate PQ.

Metal plate PQ act as a reflecting surface for sound

 

Metal tubes MA and MB

Stopwatch Normal MN Ear to hear sound

Fig. experiment to verify laws of reflection of sound

Now, by hearing the sound reflected adjust the tube MB such that you can hear maximum sound reflected. Finally fix the position of the tube on that way.
Now we see that, the reflected sound will be heard is clear and maximum at an angle of reflection which is equal to the angle of incidence 400.
Thus, from this experiment we conclude that, angle of incidence is equal to the angle of reflection.
Also, incident sound wave MA, normal MN and reflected wave Mb lies in the same plane.

3) List the applications of sound.
Ans:
Musical instruments: musical instruments like megaphones, loud speakers, and horns, musical instruments such as nathaswaram, Shania and trumpets are all constructed to send sound in specific direction without sending it in other directions.
Stethoscope: It is an instrument used in medical for listening the sound produced in the body.
SONAR: sonar is the device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
Electrocardiogram: in ECG the sound variations produced by heart is converted into electric signals.

4) Explain how does SONAR work?
Ans:
SONAR stands for Sound Navigation And Ranging. Sonar is the device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
Sonar consists of transmitter and a detector at the bottom of the boats and ships.
The transmitter produces and transmits the ultrasonic waves which are travelled through the water. This waves after striking the objects which are at the seabed, get reflected back and detected by the detector. The detector converts ultrasonic waves into electrical signals. The distance of the object from which sound is reflected is calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. If t be the time interval then the speed of sound through sea water is v = 2d/ t. Also, SONAR is the technique used to determine the depth of the sea and to locate the underwater hills, valleys, submarine and icebergs etc.

VI. Numerical problems.
1) The frequency of a source of sound is 600 Hz. Calculate the number of times it vibrates in a minute?
Ans: The no. of vibrations produced in one second is the frequency of the sound wave.
Given that, frequency of source of sound is 600 Hz, it means that 600 vibrations occurs in one second.
Then, no. of vibrations in a minute = 600* 60 seconds = 36000
Thus, in one minute 36000 no. of vibrations are produced.

2) A stone is dropped from the top of a tower 750 m high into a pond of water at the base of the tower. Calculate the number of seconds for the splash to be heard? (Given g = 10 m s–2 and speed of sound = 340 m s–1)
Ans:
Given that, height of tower = 750 m
g = 10 m/s2
Speed of sound = 340 m/s
When the stone is dropped from the top of tower, its initial velocity should be zero u = 0.
By second kinematical equation of motion, we write
s = u t + ½ a t2
Here, s means the height of the tower
750 = 0 + ½ 10* t2
t2 = 150
t = 12.24 seconds
This is the time required to reach the stone to the pond of water.
Now, after splash the sound will travels again 750 m and then it reach to the top of tower.
So speed of sound = distance covered/ time required to cover that distance
340 m/s = 750 / t
1) t = 2.20 seconds
Thus, total time to hear sound of splash = time taken by stone to reach pond of water from top of tower + time required to reach the sound to the top of tower after splash
t = 12.24 + 2.20 = 14.44 seconds
Thus, the splash to be heard after 14.44 seconds.

 

Here is your solution of Tamilnadu State Board Solution Class 9 Science Chapter 8 Sound

I hope it will help you to solve your problems & I really appreciate you for being concerned with us. 

Updated: May 26, 2021 — 2:56 pm

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