PREPARED BY V.REVATHIAMBIKA

LECTURER IN PHYSICS

SOUND

• It is the sensation that is caused by stimulation of the organs of hearing by vibrations transmitted through the air or another medium.

• It is transmitted as condensations and rarefactions in the medium. It is called a pressure wave.

• Human ear can detect only those waves whose frequency of vibrations are in the range 20 – 20000 cycles/ sec.

PRODUCTION OF SOUND

• Sound has great importance in our daily life.

• Sound makes it possible for us to communicate with one another through speech.

Musical sound gives us pleasure. Radio and Television sound gives us information and

entertainment. Horn sound of vehicles alert us.

PROPAGATION OF SOUND• Sound travels through a medium from

the point of generation to the listener. • Sound waves travel along the to and

fro movement of the vibrating objects that produce them.

• Example :Throw a stone into a pool of

water. See the circular waves spread out from the point of disturbance and travel outward on the surface of water

waves

Mechanical Waves

Longitudinal WavesEg: Sound Waves

Transverse Waves Eg: Water Waves

Electro Magnetic Waves(transverse waves)

Eg: Light Waves, Infrared, Ultraviolet, etc.,

DIFFERENCE BETWEEN TRANSVERSE AND LONGITUDINAL WAVES

TRANSVERSE WAVES LONGITUDINAL WAVES

Particles of the medium vibrate in a direction which is perpendicular to the direction of propagation.

Particles of the medium vibrate in a direction which is parallel to the direction of propagation.

Crests and troughs are formed Compressions and rarefactions are formed

Can travel through solids and surfaces of liquid

Can travel through solids , liquid and gases

Example : water waves Example : sound waves

• The maximum displacement of a particle from the mean position

• UNIT : metreAMPLITUDE(a)

• Time taken by a particleof the medium to complete one vibration

• UNIT : secondTIME PERIOD(T)

• The number of vibrations completed by a particle in one second

• UNIT : hertzFREQUENCY(n)

• Distance moved by a wave during the time a particle completes one vibration

• UNIT : metreWAVELENGTH(λ)

ECHO

• The sound waves produced by us bounce back or reflected from the forest or mountain or buildings come to our ears as Echo.

• Example : • The sound uttered by a person may be heard two or three times

after the reflection from an object. • The sensation of sound persists in our brain for about 1/10th of a

second.• Echoes may be heard more than once due to successive or multiple

reflections.• The rolling of thunder is due to the successive reflections of the

sound from a number of reflecting surfaces, such as cloud and land.

REFLECTION OF SOUND

REVERBERATION

APPLICATION OF ULTRASOUND

• Ultra sound scan is currently considered to be a safe, non-invasive, accurate and cost effective investigation of the foetus.

• It has progressively become an indispensable obstetric tool and plays an important role in the care of every pregnant women.

• Ultra sound sent by transmitter and received by the detector.

SONAR

• It is a device that uses ultrasonic waves to measure the distance, direction and speed of underwear objects and depth of the sea, locate under water hills, submarine, icebergs, sunken ship, etc.,

• ECHO Ranging :• time interval between transmission and reception

of ultrasound is “t” speed of sound through water is “ v “ total distance travelled is “ 2d “

2d = v *td = v * t /2

DOPPLER’S EFFECT

The phenomenon of the apparent change in the frequency of the source due to relative motion between the source and the observer is called as Doppler’s Effect.

Uses of Doppler effect in sound

• The doppler shift of radar waves are used in airports to find the height, speed and distance of approaching aircrafts.

• Bats send out and receive ultrasonic waves reflected by the prey and obstacles. Bats detect the location, distance and movement of the prey by the Doppler Shift.