Two practical application of reflection of sound waves are: a. Megaphones b. Stethoscope
Sound waves require a medium to travel through, which is why they are classified as mechanical waves.
a.Loudness-The amplitude of the wave determines loudness of sound. b.Pitch-The frequency of wave determines pitch of sound.
The concert hall features a curved ceiling to establish that sound is evenly distributed throughout the space, allowing it to reach every corner and area effectively.
Sound is a type of energy that produces the perception of hearing in our ears. It is produced when an object vibrates or oscillates.
Sound travels in the form of longitudinal waves through compressions and rarefactions caused by vibrating particles of the medium.
The key characteristics include frequency (pitch), amplitude (loudness), wavelength, and speed of sound.
Sound propagates as longitudinal waves, moving via compressions and rarefactions through solids, liquids, and gases faster in solids than in gases.
The speed of sound depends on the medium’s elasticity, density, and temperature; it increases with temperature and is generally higher in solids.
An echo is the reflection of sound that is heard distinctly when sound waves reflect off a surface and return to the listener after a short delay.
Reverberation is the persistence of sound due to multiple reflections in an enclosed space, whereas an echo is a single reflected sound heard distinctly.
Reflection of sound is used in megaphones and stethoscopes, while ultrasound finds use in medical imaging and industrial flaw detection.
The human ear can detect sound frequencies approximately between 20 Hz and 20,000 Hz.
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CBSE Class 9 Science Notes Chapter 11 Sound
Sound is a type of energy that moves through a medium like air, water, or solids, and is perceived by our ears. It is generated by the vibrations of objects, which produce waves that travel through the medium. As a mechanical wave, sound requires a medium to propagate and cannot travel through a vacuum, as there are no molecules present to carry the vibrations.
These CBSE Class 9 Science Notes Chapter 11 – Sound are designed to explain every concept in a clear, simple, and exam-focused manner. In this chapter, you will learn how sound is produced and propagated, the characteristics of sound waves, frequency, wavelength, amplitude, speed of sound, reflection of sound, echo, and the human ear. Our structured sound class 9 notes cover all important definitions, formulas, diagrams, and numerical concepts strictly according to the latest CBSE syllabus. These concise and easy-to-revise class 9 sound notes help strengthen conceptual understanding and ensure better performance in school exams and future competitive studies.
1.0Download CBSE Notes Class 9 Science Chapter 11 Sound: Free PDF
Get ready to explore the fascinating world of sound with our free PDF CBSE Class 9 Science Chapter 11 Sound Notes. These notes are designed to provide a clear understanding of sound waves, their properties, and various concepts that are crucial for exams.
Class 9 Science Chapter 11 Revision Notes:
2.0Sound as a Wave
Sound is the form of energy propagated as waves which our ears receive. Sound is produced by virtue of its vibrations. Sound waves cannot travel through vacuum, they need a material medium to travel.
3.0Propagation of Sound
A wave in which the particles of the medium move to and fro in the same direction as the wave's propagation is known as a longitudinal wave. Sound waves are categorized as longitudinal waves.
The longitudinal wave travels in the form of compressions and rarefactions.
Sound travels in the form of longitudinal waves and it requires a material medium for its propagation.
Example of Sound Wave-Tuning Fork-The longitudinal wave travels in the form of compressions and rarefactions.
4.0Basic Terms Connected to Waves
Wavelength-It is the distance between two consecutive points on the wave which are in the same phase.
Amplitude-It is the maximum displacement of the particle from its mean position.
Frequency-It is the number of periodic oscillations completed in one second.
f = 1/T
T is the time taken to complete one oscillation
SI Unit of Frequency is Hertz(Hz)
Wave Velocity(v)-The velocity at which energy is transmitted through a medium
Relation Between Wavelength, Frequency and Speed
Speed =Frequency ✕ Wavelength
V=f×λ
5.0Speed of Sound
The flash of lightning due to collision of clouds is seen much before the thunder, although both occur simultaneously. This happens because the velocity of light is greater than the velocity of sound.
The speed of sound is governed by the properties of the medium it travels through, which can vary in terms of elasticity, density, pressure, and temperature.
The speed of sound decreases as it moves from solid to gaseous state. But in any medium the speed of sound increases with increase in temperature.
6.0Reflection of Sound
When sound is incident on a solid or a liquid surface bounce off the surface like light rays.
Sound waves also obey the laws of reflection and refraction. For sound waves to reflect, we need extended surface or obstacles of larger size. For example, the rolling of thunder is due to successive reflection from cloud and land surfaces.
According to the law of reflection of sound, the angle at which sound waves strike the reflecting surface is equal to the angle at which they are reflected. Both angles, along with the normal to the reflecting surface, lie in the same plane.
7.0Echoes
When we shout or clap near a reflective surface like a tall building or mountain, we will hear the sound repeated after a short delay. This repeated sound is known as an echo.
Echoes are produced when sound is reflected by a hard surface. An echo can be heard distinctly only if the time interval between the original sound and reflected sound is greater than 0.1s.This is because the sensation of sound persists in our brain for about 0.1s.
8.0Reverberation
In a large hall, a sound will continue to linger due to repeated reflections from the walls until it diminishes to a level where it is no longer audible. This phenomenon, where sound persists through multiple reflections, is known as reverberation.
Persistence of sound after the source has stopped as a result of repeated reflections from walls, ceiling and other surfaces is called reverberation. Reverberation characteristics are important in the design of concert halls, theatres etc.
9.0Practical Application of Reflection of Sound
Megaphone
Hearing Aid
Sound Board
Stethoscope
10.0Range of Hearing
Sound waves are emitted from a vibrating source and transmitted through air. The human ear is capable of hearing sound waves within the range of 20Hz to 20 KHz. This range is known as audible range.
The sound wave having frequencies above the audible range are known as ultrasonic waves and it is usually referred as Ultrasound.
The sound waves having frequencies less than the audible range are called infrasonic waves.
11.0Application of Ultrasound
It is used for medical diagnosis and therapy and also as a surgical tool.
It is used as a tool in the treatment of muscular pain.
It is employed to identify cracks and imperfections in metal blocks.
Bats and Porpoises use ultrasound for navigation and to locate food in darkness.
12.0Key Features of Class 9 Science Notes Chapter 11 Sound
Detailed Conceptual Explanation: Thorough coverage of sound-related topics such as the nature of sound, propagation of sound, speed of sound, reflection of sound, and the Doppler effect.
CBSE-Aligned Content: The notes are crafted to meet the CBSE Class 9 syllabus, ensuring all essential concepts and experiments are included.
Easy-to-Understand Language: Complex topics are explained in simple and straightforward language, making it easier for students to grasp key concepts like vibrations, frequency, and amplitude.
Clear Diagrams and Illustrations: Visual aids like labeled diagrams of sound waves, the human ear, and sound propagation help in better understanding and retention.
