Question

class 9 sound chapter easy notes

Answer 1

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⭐️⭐️Here, you will get the CBSE Class 9 Science, Sound: Chapter notes (Part-I). These chapter notes are prepared by the subject experts and cover every important topic from the chapter. You get a crisp and brief explanation of all these topics so as to make your learning easy and organized. At the end of the notes you can try the questions asked from the discussed set of topics. These questions will help you to track your preparation level and get a hold on the subject.

❤️Main topics covered in this part of CBSE Class 9 Science, Sound: Chapter Notes, are:❤️

✔️Sound-Production and Propagation
✔️Medium
✔️Wave and its Types
✔️Characteristics of Sound
✔️Audible Frequency
✔️Reflection of Sound and its Laws
✔️Applications of Reflection of Sound
✔️Key notes for Chapter - Sound, are:

❤️Sound❤️

Sound is a form of energy which produces a sensation of hearing in our ears.

❤️Production of Sound ❤️

❤️Sound is produced due to the vibration of objects. Vibration is a periodic back-and-forth motion of the particles of an elastic body or mediumkind about a central position. It is also named as oscillation.
For example:

❤️Stretched strings of a guitar vibrate to produce sound. When membrane of a table is struck, it vibrates to produce sound.
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, the particles around the medium vibrate. The particle in contact with the vibrating object is first displaced from its equilibrium position. Each particle disturbs the other particle in contact. Thus, the disturbance is carried from the source to the listener.

❤️Only the disturbance produced by the vibrating body travels through the medium but the particles do not move forward themselves.

✨Medium✨

The matter or substance through which sound is transmitted is called a medium.
A medium is necessary for the propagation of sound waves.
The medium can be solid, liquid or gas.
Sound cannot travel in vacuum.
Wave that requires medium to propagate is called Mechanical wave.

✨Wave✨

Wave is a phenomenon or disturbance in which energy is transferred from one point to another without any direct contact between them. For example: Heat, light and sound is considered as a wave.

✨Types of Waves✨

(i) Longitudinal waves

(ii) Transverse waves

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Answer 2

Notes on Sound ( Class 9 )

A sound is because of wave and a wave is because of vibratory motion of particles of medium.

In order to understand how sound travels we need to understand that in what waves sound travels.

➣ Transverse waves : In a transverse wave, the movement of particles is perpendicular (up and down from their mean position) to the direction of prorogation of waves.

➣ Longitudinal waves : In longitudinal waves, the particles which are parallel, pushes each other forming compression and rarefaction. Thus the particles moves to and fro from their mean position in the direction of propagation of waves.

Compressions : The region with more density of particles due push.

Rarefaction : The region with less density of particles or with less concentration.

➣ Mechanical waves : The waves that need the medium to travel are called mechanical waves. These waves can be transverse or longitudinal. Eg - Sound waves, water waves.

➣ Electromagnetic waves : Waves that don't need medium to travel and can travel in vacuum. These waves can only be transverse. Eg - X ray waves, light waves etc.

What are sound waves?

Sound waves are the longitudinal waves i.e., particles move to and fro from their mean position but not actually any particle move from one place to another. Only the vibratory motion of particles move from one place to other and we term it as wave.

➣ Features of Sound

Frequency = The number of waves produced per second. The pitch depends on frequency. The symbol of frequency is ( nu ) and its SI unit is Hertz ( Hz ).

Wavelength = The distance between two consecutive compression or rarefaction is called wavelength. The symbol is ( lambda ) and its SI unit is meter ( m ).

Amplitude = The maximum displacement of particles from their mean position is called amplitude. Loudness directly depends of amplitude, its unit is decibel (dB). SI unit is meter ( m ).

Time period = The total time taken to produce one complete wave. Denoted by T and its SI unit is second ( s ).

Speed = The distance travelled by wave in per unit time. SI unit is m/s.

Quality/timber = The smoothness of soynd waves decide how sound is good or bad.

Tone = The same type of frequency.

Note = Different types of frequency or tones make a note.

Intensity of sound : The amount of energy produced on the path of wave at per square unit area.

Formula derivation :-

Speed = distance / time

s = Wavelength / time

s = wavelength × frequency.

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