Sound

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Sound

  1. 1. 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 ?)
  2. 2. 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.
  3. 3. 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
  4. 4. 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
  5. 5. Sound travels in form of waves Longitudinal waves
  6. 6. Characteristics of a wave
  7. 7. Characteristics of waves Amplitude Wavelength Frequency Time period Velocity of wave Play
  8. 8. 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.
  9. 9. 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.
  10. 10. 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.
  11. 11. 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
  12. 12. Velocity of wave • The distance travelled divided by the time taken. • Velocity (v) = Distance (λ) / Time taken (T) v = λ x f
  13. 13. How sound is produced Sound travels due to vibrations (disturbance) produced in the medium. • Video 1 • Video 2 • Video 3 • Video 4
  14. 14. How sound travels Sound travels through material medium in the form of compression and rarefaction. • Video 1 • Video 2 • Video 3
  15. 15. 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.
  16. 16. Speed of sound 1 Mach (M) = 334 m/sec • Subsonic: M < 1 • Sonic: M = 1 • Supersonic: 1 < M < 5 • Hypersonic: M > 5
  17. 17. 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
  18. 18. 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…..
  19. 19. 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.
  20. 20. 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
  21. 21. 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.
  22. 22. Thank You !

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