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    Sound

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    Thnderbeast Gaming

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    Sound

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    Sound

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    Thnderbeast Gaming

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    DEPARTMENT OF SCIENCE 2023-2024

    CHAPTER 12-SOUND

    GRADE –9-PHYSICS

    PREPARED BY-Ms. MANJUSHA VIPIN

    REVIEWED BY-Ms. SANDHYA KV

    DURATION: -8th January to 14th January 2024

    LEARNING OBJECTIVES

    • To explain the properties of sound waves

    CONTENT

    Introduction to waves
    A wave is a disturbance in a medium which moves from one point to another and
    carries energy without a net movement of particles. It may take the form of elastic
    deformation or a variation of pressure.
    E.g: Rubber cork on the water that goes up and down when a rock falls in the water
    creates a ripple.

    Particle motion of mechanical waves


    (i) Transverse Waves
    Particle motion is perpendicular to the direction of wave motion. This type of wave
    is a mechanical wave.
    E.g: Light and Mexican wave in a stadium.
    (ii) Longitudinal waves
    Particles travel parallel to the direction of wave motion, by means of successive
    compressions or elongations. This is also a mechanical wave.
    E.g: Sound waves in air.
    Sound Properties

    Introduction to sound waves


    Sound needs a medium to propagate. The matter or material through which
    sound propagates is called a medium. When particles vibrate about their mean
    positions, it pushes a region of compressed air, creating a region of high pressure,
    followed by a region of low pressure as the particle retreats to its mean position.
    The sound wave propagates by compressions and rarefactions of particles in
    a medium. Sound propagation can be visualised as the propagation of pressure
    variations in the medium.

    Characteristics of Sound Waves

    Wavelength
    The distance between two successive crests or troughs (or) successive compressions
    and rarefactions is called as wavelength (λ). The SI unit of wavelength is metre (m).
    Time period
    Time taken by two consecutive compressions or rarefactions to cross a fixed point is
    called a Time period (T). The SI unit of time in seconds (s).

    Frequency
    The number of compressions or rarefactions per unit time is called frequency (𝛎).
    The SI unit of frequency is Hertz. The SI unit is Hertz (s−1)
    v=1/T
    Speed (v), wavelength (λ) and frequency (𝛎) are related as v=λ𝛎

    Amplitude
    The magnitude of disturbance in a medium on either side of the mean value is
    called an amplitude (A).
    As shown in the figure below, the unit of amplitude will be the density or pressure.
    Distance between mean position and crest (maximum displacement).

    Amplitude (A)

    Pitch
    The number of compressions or rarefactions per unit time. Directly proportional to
    frequency.
    Representation of low and high pitch

    Volume
    Volume or loudness of a sound depends on the amplitude. The force with which an
    object is made to vibrate gives the loudness.

    Higher force → higher amplitude → louder sound


    The amount of sound energy flowing per unit time through a unit area is called the
    intensity of sound.
    The Intensity of Sound

    Note and Tone


    A sound of a single frequency is called a tone. A sound produced with a mixture of
    several frequencies is called a note.

    Quality of sound
    The richness or timber of sound is called the quality. Sound with the same pitch
    and loudness can be distinguished based on the quality. Music is pleasant to the
    ears while noise is not. But they both can have the same loudness and pitch.

    Speed of sound
    Sound travels through different media with different speeds. Speed of sound
    depends on the properties of the medium: pressure, density and temperature
    Speed of sound: Solids > Liquids > Gases
    Speed of sound in air = 331 m/s at 00C and 344 m/s at 22∘ C
    When a source emits sound with a speed greater than the speed of sound in air, it
    creates a sonic boom which produces shockwaves with lots of energy. They produce
    a very loud noise which is enough to shatter glass and damage buildings.

    LOC:
    • The students will be able to solve the questions based on the topic properties
    of sound waves.
    COMPETENCES:
    Critical thinking, Problem solving.

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