Sound is a mechanical wave that requires a medium to travel through and cannot travel through a vacuum. Sound waves are longitudinal waves that cause compressions and rarefactions as they propagate. Key characteristics of waves include amplitude, wavelength, frequency, time period, and velocity. The human ear can detect sounds between 20-20,000 Hz. Ultrasound has a frequency above this range and can be used for medical imaging and other applications like SONAR.

2. 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 ?)

3. 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.

4. 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

5. 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

6. Sound travels in form of waves
Longitudinal waves

7. Characteristics of a wave

8. Characteristics of waves
Amplitude
Wavelength
Frequency
Time period
Velocity of wave
Play

9. 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.

10. 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.

11. 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.

12. 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

13. Velocity of wave
• The distance travelled divided by the time taken.
• Velocity (v) = Distance (λ) / Time taken (T)
v = λ x f

14. How sound is produced
Sound travels due to vibrations
(disturbance) produced in the medium.
• Video 1
• Video 2
• Video 3
• Video 4

15. How sound travels
Sound travels through material medium in
the form of compression and rarefaction.
• Video 1
• Video 2
• Video 3

16. 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.

17. Speed of sound
1 Mach (M) = 334 m/sec
• Subsonic: M < 1
• Sonic: M = 1
• Supersonic: 1 < M < 5
• Hypersonic: M > 5

18. 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

19. 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…..

20. 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.

21. 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

22. 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.

23. Thank You !