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    Sound

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    byas26goswami

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    © All Rights Reserved
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    Sound

    Uploaded by

    byas26goswami
    2 views7 pages

    Original Title

    240815110852146353Sound

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    2 views7 pages

    Sound

    Uploaded by

    byas26goswami

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    SOUND

    Sound is a form of energy that produces the


    sensation of hearing in our ears.
    Sound is produced by vibrations so Sound
    is produced when a body vibrates.
    A vibrating body is a source of sound.

    Sound is a form of energy:

    Mechanical energy is required to start vibrations in a body


    producing sound.
    The vibrations of body are transmitted in, medium in form of
    waves from that point to the next and so on.
    These waves on reaching our ears, produce vibrations in the ear
    drum which are perceived as sound by us. Thus, sound is a form
    of energy.

    SOUND PROPAGATION REQUIRES A MATERIAL MEDIUM


    A material medium is necessary for the propagation of sound
    from one place to another.
    (i) The medium must be elastic so that its particles may come
    back to their initial positions after displacement on either side.
    (ii) The medium must have inertia so that it particles may store
    mechanical energy.
    (iii) The medium should be frictionless so that there is no loss of
    energy in propagation of sound through it.
    Sound can propagate not only in gases, but also in solids and
    liquids. On the other hand, blanket, thick curtains etc., absorb
    most of the sound incident on them and transmit or reflect only a
    small fraction of it.
    Sound cannot travel in vacuum. On moon, there is no medium, so
    one cannot hear the sound produced by others.

    PROPAGATION OF SOUND IN A MEDIUM

    The compression and rarefaction regions are produced one after


    the other which carry the disturbance with it. This wave in which
    the particles of medium vibrate about their mean positions, in the
    direction of propogation of sound, is called a longitudinal wave.
    Thus sound travels in air in form of longitudinal waves.

    We notice that the cork does not move ahead, but it moves up
    and down, while the wave moves ahead. The reason is that the
    particles of water (or medium) start vibrating up and down at the
    point where the stone strikes.
    The wave in which the particles of medium vibrate about their
    mean positions, in a direction perpendicular to the direction of
    propagation of the wave, is called the transverse wave. A
    transverse wave is composed of crest and trough. The position of
    maximum upward displacement is called crest, while the position
    of maximum downward displacement is called trough.
    Transverse waves can only be produced in solids and on the
    surface of liquids.

    Characteristics of wave motion :


    (1) A wave is produced by the periodic disturbance at a point in
    the medium.
    (2) Due to propagation of wave in a medium, the particles of
    medium vibrate about their mean positions

    SOME TERMS RELATED TO WAVE MOTION


    (i) Amplitude: When a wave passes through a medium, the
    maximum displacement of the particle of medium on either side
    of its mean position, is called the amplitude of wave. It is denoted
    by the letter a. Its S.I. unit is metre (m).
    (ii) Time period: The time taken by a particle of medium to
    complete its one vibration is called the time period of wave. It is
    denoted by the letter T. Its S.I. unit is second (s).
    (iii) Frequency: The number of vibrations made by a particle of
    medium in one second is called the frequency of wave. Its S.I. unit
    is second-¹ (symbol s¹) or hertz (symbol Hz).
    (iv) Wavelength: The distance travelled by the wave in one time
    period of vibration of particle of the medium, is called its
    wavelength. It is denoted by the letter (lambda). Its S.I. unit is
    metre (m).
    (v) Wave velocity: The distance travelled by a wave in one second
    is called its wave velocity or wave speed. Its S.I. unit is metre per
    second (m.s.¹).

    Relationship between the Wavelength, Wave Velocity and


    Frequency

    The speed of sound in a medium depends on the following two


    factors:
    (i) the elasticity E of the medium, and
    (ii) the density p of the medium.

    The speed of sound is different in different media. The speed of


    sound is more in solids, less in liquids and least in gases.
    Example showing that the speed of sound in steel is more than
    that in air :-
    A person living near the railway track often presses his ear
    against the steel rail to guess whether a train is coming or not.

    FACTORS AFFECTING THE SPEED OF SOUND IN A GAS


    (i) Effect of density: The speed of sound is inversely proportional
    to the square root of density of the gas.
    (ii) Effect of temperature: The speed of sound in a gas increases
    with the increase in temperature of the gas.
    (iii) Effect of humidity: The speed of sound in air increases with
    the increase in humidity in air.
    (iv) Effect of direction of wind: The speed of sound increases or
    decreases according to the direction of travel of wind.

    FACTORS NOT AFFECTING THE SPEED OF SOUND IN A GAS


    (i) Effect of pressure
    (ii) Effect of amplitude of wave
    (iii) Effect of wavelength (or frequency) of wave

    COMPARISON OF SPEED OF SOUND WITH SPEED OF LIGHT


    (1) The light waves can travel in vacuum, but he sound waves
    cannot travel in vacuum.
    (2) The speed of light waves is 3 x 108 m/s speed of sound waves
    in air (i.e., 330 m/s at 0°C).
    (3) The speed of light waves decreases in an optically denser
    medium while the speed of sound waves is more in solids, less in
    liquids.
    (4) The light waves are transverse electromagnetic waves while
    the sound waves in air are longitudinal mechanical waves.

    (1) Thunder and lightning: In thunder, light is seen much earlier


    than the sound of thunder is heard, although they are produced
    simultaneously. The reason is that light takes almost negligible
    time in comparison to sound. in reaching us from the place of
    thunder because speed of light is much more (= 3 x 108 m s-¹)
    than the speed of sound (= 330 m s-¹).

    (2) When the starter in an athletic event fires a gun, a spectator


    sitting at a distance hears the sound of fire a little later while the
    smoke is instantaneously seen.

    INFRASONIC, SONIC AND ULTRASONIC FREQUENCES


    The human ear is able to hear sound in a frequency range of
    about 20 Hz to 20.000 Hz (or 20 kHz) i.e.. the audible range of
    frequency is 20 Hz to 20 kHz. The human ear is most sensitive in
    the range 2000 Hz to 3000 Hz, where it can hear even a very feeble

    sound.
    The sound of frequencies in the range 20 Hz to 20 KHz is called
    the sonic or audible sound, the sound of frequency less than 20
    Hz is known as infrasonic sound (or simply infrasonic), while the
    sound of frequency greater than 20 kHz is known as ultrasound
    (or ultrasonic).

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