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    9780 - Week 2 - Sound Waves

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    vivianada683
    A short note on sound waves

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    9780 - Week 2 - Sound Waves

    Uploaded by

    vivianada683
    6 views3 pages
    A short note on sound waves

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    9780_Week 2- Sound Waves

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    A short note on sound waves

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    6 views3 pages

    9780 - Week 2 - Sound Waves

    Uploaded by

    vivianada683
    A short note on sound waves

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    Week: 2.

    Class: SS 2

    Subject: Physics.

    Topic: Sound waves.

    Noise and music: Sound can be classified into noise and musical notes. Noise is due to
    vibrations of irregular frequency such as the rattling of a wheel on a rough road.

    Music is produced by vibrations of regular or constant frequency.

    Characteristics of musical note are as follows: pitch, loudness, and quality.

    Pitch of a note is its position on the musical scale. It is the degree of highness or lowness of
    sound as perceived by the listener. Pitch depends on frequency.

    Loudness is the magnitude of the sensation resulting from a sound reaching the ear. It
    depends on the amplitude of vibration of the body.

    Intensity is the rate of flow of sound energy per unit area perpendicular to the direction of
    propagation of the sound waves.

    Quality or Timbre is a characteristic note of a musical instrument which distinguishes it


    from another note of the same pitch and loudness produced by another instrument. It
    depends on the overtones accompanying the fundamental note. Like light, sound waves
    can be reflected, refracted, diffracted and also show their interference phenomenon.

    Echoes : echo is a sound heard after the reflection of sound waves from a plane surface.
    Reverberation is the perseverance of the sound after the source ceases. It is due to
    multiple reflection or echo of the original sound.

    Application/Uses of echoes are as follows:

    1. The determination of the velocity of sound.


    2. The determination of the depth of sea beds
    3. In oil and gas exploration
    4. In sub marines.
    The formulae is given as t= 2x÷v, where x = distance between the source of sound and
    the reflecting surface. V= velocity of sound in air medium (air, water,glass, metal etc).

    Example: A man standing 510m away from a wall sounds a whistle, the echo from the
    wall reaches him 3seconds later. Calculate the velocity of sound in air. (NECO 2000)

    Solution:

    Distance x= 510m

    echo t =3s,

    velocity v =?

    Using the formulae: t =2x÷v

    vt =2x,

    v =2x÷t = 2× 510÷3

    =1020÷3

    =340m/s.

    Forced vibrations : vibrations that result from an external periodic force acting on a system
    and setting vibrating at the same frequency as the external periodic force.

    Resonance : is a phenomenon which occurs whenever a particular body or system is set in


    oscillation at its own natural frequency as a result of impulses or signals received from some
    other systems or body which is vibrating with the same frequency.

    Harmonics : are whole number multiples of the fundamental frequency fo is the first
    harmonic, 2fo,3fo etc are the second and third harmonics.

    Overtones: are the next higher frequencies produced after the fundamental frequency by a
    vibrating body overtone may or may not be harmonics of the fundamental. Stationary waves
    are produced when two waves with the same frequency and amplitude travelling in opposite
    directions are superposed. Nodes are points on a stationary waves which are at rest.
    Antinodes are points where the amplitude of vibration is maximum.

    Vibration of Strings: the length L of the string is equal to wavelength ÷2 ,

    wavelength = 2L for a sound wave


    v= wavelength ×frequency f and

    frequency = velocity ÷wavelength.

    Substitute wavelength =2L

    fo = v÷2L

    Example : find the frequency of the first harmonic of a piano string of length 1.5m. If the
    velocity is 120m/s

    Solution:

    first harmonic L wavelength ÷2 ,

    wavelength =2×L

    frequency f =velocity ÷wavelength

    = 120÷2×1.5

    =120÷3

    =40Hz .

    Class work: find the second and third harmonics.

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