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    Sound Sound Presentation Transcript

    • Sound • Sound means basically the mechanical vibrations. • These vibrations require a material medium to travel through. eg : Solid, liquid, gas, plasma • Meaning Sound cannot travel through Vacuum. (Why ?)
    • Sound as Wave • Sound travels in the form of waves. • Wave : A wave is a disturbance that propagates through space and time, usually with transference of energy. • Waves travel and transfer energy from one point to another, often with no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); they consist oscillations or vibrations (of particles) around almost fixed locations.
    • Types of waves • Transverse Wave : Transverse waves are those with vibrations perpendicular to the direction of the propagation of the wave; examples include waves on a string, and electromagnetic waves. • eg. : Light (i.e. Electromagnetic waves) http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35
    • Types of waves • Longitudinal waves : Longitudinal waves are those with vibrations parallel to the direction of the propagation of the wave. eg : Sound wave, Mechanical waves http://www.surendranath.org/Applets/Waves/Lwave01/Lwave01Applet.html
    • Sound travels in form of waves Longitudinal waves
    • Characteristics of a wave
    • Characteristics of waves Amplitude Wavelength Frequency Time period Velocity of wave Play
    • Wavelength (λ) •The distance between any two adjacent wave crests1 (wave crests that are next to each other) or any two adjacent wave troughs2 in a wave. 1. Crest: The highest point reached by a wave. 2. Trough: The lowest point reached by a wave.
    • Amplitude (A) •The maximum displacement (difference between an original position and a later position) of the material that is vibrating. Amplitude can be thought of visually as the highest and lowest points of a wave.
    • Time period (T) http://library.thinkquest.org/11924/waveBoard.html • It is the time taken by a wave to complete a certain number of fixed oscillations. Usually of 1 wavelength.
    • Frequency (f/n) •The number of wave crests (or wave troughs) that pass a given point per unit of time (usually per second). • Frequency (f) = 1 / Time Period (T) • SI unit of ‘f’ is Hertz (Hz). • Hz = 1 / sec
    • Velocity of wave • The distance travelled divided by the time taken. • Velocity (v) = Distance (λ) / Time taken (T) v = λ x f
    • How sound is produced Sound travels due to vibrations (disturbance) produced in the medium. • Video 1 • Video 2 • Video 3 • Video 4
    • How sound travels Sound travels through material medium in the form of compression and rarefaction. • Video 1 • Video 2 • Video 3
    • Speed of sound • It is the speed with which a sound pulse travels from the source to the observer. • Sound travels through air at NRTP with 334 m/s. Factor affecting speed of sound : Density of medium : Speed of sound is directly proportional to the density of the medium.
    • Speed of sound 1 Mach (M) = 334 m/sec • Subsonic: M < 1 • Sonic: M = 1 • Supersonic: 1 < M < 5 • Hypersonic: M > 5
    • Reflection of sound • We know, <i = <r (Refer practical sheet) • Some examples : Stethoscope, Soundboard • Lets see some more examples : • Video 1 • Video 2 • Video 3
    • Echo • Reflection of sound is called Echo. • We can hear two consecutive sounds only if there is a time gap of 1/10th of a second (0.1s). • Note that this value is only for sound in air and will be different for different mediums. • Let us calculate the minimum distance to hear a Echo…..
    • Reverberation • Basically it is unwanted Echo. • Reverberation in a hall can be avoided by use of : i. Panels made of porous & soft materials. ii.Using floor carpets iii.Using curtains, sofa sets etc.
    • Human Ear • Human ear senses sound by the vibration of ear drums. eg: Video 1 , Video 2, Video 3 • The human can hear all the frequencies between 20 – 20,000 Hz. • Frequencies < 20 Hz are called Infrasonic. eg : Whales • Frequencies > 20,000 Hz are called Ultrasonic. eg : Bats
    • Ultrasound •As ultrasound have high frequency they have high energy & high penetration power which makes it helpful in many tasks. Eg : i . To study internal organs in body. ii. To study the development of fetus. iii. To break kidney stones. iv. Used in SONAR. SONAR (SOund Navigation And Ranging) is a technique that uses Ultrasonic frequency to navigate, communicate with or detect other vessels & to study the landscape.
    • Thank You !