Propagation of Sound Waves Selina 9th Concise Physics Solutions

Propagation of Sound Waves Selina ICSE 9th Concise Physics Solutions  Chapter-8 Propagation of Sound Waves. Step By Step Revised Concise Selina Physics Solutions of Chapter-8 Propagation of Sound Waves with Exe-8(A) , MCQ 8(A), Num-8(A) , Exe-8(B), MCQ -8(B) including Numerical and MCQ Questions Solved. Revised Selina Concise Physics Solutions Propagation of Sound Waves Chapter-8 for ICSE Class-9. Visit official Website CISCE for detail information about ICSE Board Class-9.

Propagation of Sound Waves Selina Concise 9th Physics Solutions

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Note :-  Before Viewing Selina Concise Physics Solutions of Chapter-8 Propagation of Sound Waves for ICSE Class-9 Physics. Read the whole chapter carefully and Solved all example of Chapter-8 Propagation of Sound Waves for Class-9 Physics.

 latest syllabus of council class 9th physics

According to latest syllabus of council class 9th physics, Law of reflection, character of image, Spherical Mirror, Ray diagram and use of spherical mirror, Type of mirror, radius of curvature, Pole, Principal Axis, Focus and Focal Length.

Name of sound wave, Requirement of a medium for sound waves to travel; Propagation and speed in different media; comparison with speed of light. Sound propagation, terms- Frequency (f), wavelength, velocity, relation, effect of different factors on the speed of sound.

Exe-8(A) Propagation of Sound Waves Physics concise selina solutions

Question 1

What causes sound?


Answer 1

Sound is caused due to vibrations of a body.

Question 2

What is sound? How is it produced?

Answer 2

Sound is a form of energy that produces the sensation of hearing in our ears. Sound is produced by a vibrating body.

Question 3

Complete the following sentence:

Sound is produced by a ___________ body.

Answer 3


Question 4

Describe a simple experiment which demonstrates that the sound produced by a tuning fork is due to vibrations of its arms.

Answer 4

Experiment: A tuning fork is taken and its one arm is struck on a rubber pad and it is brought near a tennis ball suspended by a thread as shown in figure.


vibreation of sound

It is noticed that as the arm of the vibrating fork is brought close to the ball, it jumps back and forth and sound of the vibrating tuning fork is heard. When its arm stop vibrating, the ball becomes stationary and no sound is heard.

Question 5 

Describe in brief, with the aid of a sketch diagram, an experiment to demonstrate that a material medium is necessary for propagation of sound.

Answer 5

Experiment to demonstrate that a material medium is necessary for the propagation of sound:

An electric bell is suspended inside an airtight glass bell jar. The bell jar is connected to a vacuum pump as shown in figure. As the circuit of electric bell is completed by pressing the key, the hammer of the electric bell begins to strike the gong repeatedly due to which sound is heard.

electric bell

Keeping the key pressed, air is gradually withdrawn from jar by starting the vacuum pump. It is noticed that the loudness of sound goes on decreasing as the air is taken out from the bell jar and finally no sound is heard when all the air from the jar has been drawn out. The hammer of the electric bell is still seen striking the gong repeatedly which means that sound is still produced but it is not heard.

When the jar is filled with air, the vibrations produced by the gong are carried by the air to the walls of jar which in turn set the air outside the jar in vibration and sound is heard by us but in absence of air, sound produced by bell could not travel to the wall of the jar and thus no sound is heard. It proves that material medium is necessary for the propagation of sound waves.

Question 6

There is no atmosphere on moon. Can you hear each other on the moon’s surface?

Answer 6

We cannot hear each other on moon’s surface because there is no air on moon and for sound to be heard, a material medium is necessary.

Question 7

State three characteristics of the medium required for propagation of sound?

Answer 7

Requisites of the medium for propagation of sound:

(i) The medium must be elastic.

(ii) The medium must have inertia.

(iii) The medium should be friction less.

Question 8

Explain with an example, the propagation of sound in a medium.

Answer 8

Take a vertical metal strip with its lower end fixed and upper end being free to vibrate as shown in fig (a).

As the strip is moved to right from a to b as shown in Fig (b), the air in that layer is compressed (compression is formed at C). The particles of this layer compress the layer next to it, which then compresses the next layer and so on. Thus, the disturbance moves forward in form of compression without the particles themselves being displaced from their mean positions.

As the metal strip returns from b to a as shown in Fig (c) after pushing the particles in front, the compression C moves forward and particles of air near the strip return to their normal positions.

When the strip moves from a to c as shown in Fig (d), it pushes back the layer of air near it towards left and thus produces a low pressure space on its right side i.e. layers of air get rarefied. This region is called rarefaction (rarefaction is formed at R).

When the strip returns from C to its mean position A in Fig (e), the rarefaction R travels forward and air near the strip return to their normal positions.

Thus, one complete to and fro motion of the strip forms one compression and one rarefaction, which together form one wave. This wave through which sound travels in air is called longitudinal wave.

motion of a sprit

Question 9

Choose the correct word/words to complete the following sentence:

When sound travels in a medium ____________ (the particles of the medium, the source, the disturbance, the medium) travels in form of a wave.

Answer 9

the disturbance

Question 10

Name the two kinds of waves in form of which sound travels in a medium.

Answer 10

Sound travels in a medium in form of longitudinal and transverse waves.

Question 11

What is a longitudinal wave? In which medium: solid, liquid or gas, can it be produced?

Answer 11

A type of wave motion in which the particle displacement is parallel to the direction of wave propagation is called a longitudinal wave. It can be produced in solids, liquids as well as gases.

Question 12

What is a transverse wave? In which medium: solid, liquid or gas, can it be produced?

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