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 wavesLongitudinal waves

Characteristics of a wave

Characteristics of waves

Amplitude

Wavelength

Frequency

Time period

Velocity of wave

Play

Wavelength •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 () / Time taken (T) v = 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 atechnique that uses Ultrasonic frequency tonavigate, communicate with or detect othervessels & to study the landscape.

Thank You !