Production and Propagation of Sound Waves

•    Every sound is produced by vibrations. Vibration is the backend forth movement of an object. While speaking, vibrations are produced in our vocal cords. A sound heard when sound energy reaches our ears.
•    Sound propagates in the form of waves.

                                        

Sound waves are longitudinal waves which makes compression and rarefaction. A longitudinal wave is defined as a moving wave that consists of oscillations occurring in the direction of the direction of energy transfer.
Compression: The region of high pressure, developed due to vibration of string, is known as compression
Rarefaction: The region of low pressure, developed due to vibration of string, is known as compression rarefaction.
•    Sound can travel through solids, liquids and gases but not through vacuum. Depending upon how quickly the medium particles can interact with each other, the speed of sound varies in different mediums. It is fastest in solid while slowest in gases.
•    A transverse wave is another kind of wave that consists of oscillations occurring perpendicular to the direction of energy transfer.

                                             

•    Wavelength, frequency, amplitude, time period and wave velocity are important terms related to wave motion.
Wavelength is defined as the distance between two consecutive compressions or rarefactions. It is measured in metres.
Frequency is the number of periodic oscillations per unit time.
Time period is the time taken by the sound wave to complete one oscillation in a medium.
Amplitude is the maximum displacement of the particles from its mean position.  
Wave velocity is defined as distance travelled by wave per second. Wave velocity is equal to the product of frequency and wavelength of the respective wave.
•    On the basis of frequency, sound waves are classified as
Infrasonic: The sound waves below 20 Hz are called infrasonic
Audible sound: Audible sound for humans ranges from 20 Hz to 20 kHz.
Ultrasonic sounds: Sound waves above 20 kHz are called ultrasonic. Ultrasounds get many applications in medical fields and industries.
•    If the speed of an object more than the speed of sound then its speed is termed as supersonic.

 

 

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  • Q1

    State a difference between infrasonic and ultrasonic vibrations.

    Marks:1
    Answer:

    Infrasonic vibrations are those vibrations which have frequency less than 20 Hz whereas ultrasonic vibrations are those vibrations which have frequency more than 20 KHz.

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  • Q2

    What is sound?

    Marks:1
    Answer:

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

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  • Q3

    How sound propagates through a medium? Explain with the help of example.

    Marks:5
    Answer:

    1. Strike the hammer on the drum and we hear the sound.

    2. During the propagation of sound the particles of mediumstarts vibrating.

    3. When an object vibrates then the particles of the medium get displaced from their equilibrium positions and strike their neighbouring particles.

    4. Then the first particle comes back to its initial position, now neighbouring particles also get displaced from their mean positions.

    5. In this way vibration reaches to the listener through vibrating particles in form of wave.

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  • Q4

    What do you mean by longitudinal waves?

    Marks:2
    Answer:

    Waves in which particles of medium displace in the direction parallel to the direction of propagation of wave.

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  • Q5

    What do you mean by transverse waves?

    Marks:2
    Answer:

    Transverse waves are those waves in which particles of medium displace perpendicular to the direction of propagation of wave.

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