SOUNDClass X - Physics

Module Objectives

• Understand Sound – frequency and behaviour.

• Ultrasonic sound and infrasonic sound.

• Applications of ultrasonic sound.

• SONAR in detail.

• Ultrasound scanner in detail.

• Doppler Effect.

Introduction

• Sound

form of energy

produced by vibration of bodies

propagated in the form of waves. What is a wave? A wave is a periodic disturbance propagating through a medium,

carrying energy. A wave is described in terms of its frequency (f) wavelength (Λ) and velocity (v).

These are related by the equation

Through material medium

Sound

• When a drum is struck

• The drumhead vibrates

• The vibrations are transmitted through the air in the form of waves.

• When they strike the ear, these waves produce the sensation of sound.

Interesting Facts about Sound

Light travels faster than sound. eg. the lightning before you hear the thunder. eg.- When you hear an airplane, look up! If the plane is up high, and

you look at it, the sound will seem to be coming from BEHIND the plane, instead of straight from the plane. That's because the light that is reflecting off the plane into your eyes is much faster than the sound that the plane's jet engines are making.

Sound travels through air at about 770 miles per hour. The speed of sound changes depending on the temperature - warmer days

make sound travel faster colder days make it travel slower WHY???This is because the air is less dense on warm days, so there aren't as

many air molecules to move to get the sound from point A to point B

Echo – reflection of Sound

Types Of Sound

• Vibrations of any body can produce a wide range of frequencies.

• Audible range = 20Hz to 20,000 Hz(for humans)

• Infrasound - below the range of human hearing

• Ultrasound - above the range of human hearing(another name of ultrasonic sound).

• Animals such as cats, dogs and bats can hear sounds of other frequencies.

Topic

Properties of Infrasonic and Ultrasonic sound

Ultra sonic Sound• Frequency Range = 20kHz to 5 x 105 kHz.• Range of wavelengths is from 1.65 cm to about 6 x 10-5 cm.• Branch of science that deals with ultrasound is called ultrasonics• Propagation – similar to sound wave• Speed - same as sound wave• Energy – higher than normal sound due to high frequency.

Infrasonics Sound• Sounds of frequency below 20Hz

Uses Of Sound

• NDE = NONDESTRUCTIVE EVALUATION

Uses of Ultrasonic waves

• Study of ultrasonic waves in a medium gives information about its physical properties like elasticity, configuration of atoms etc.

• Detect cracks and flaws in metal moldings.• Manufacture alloys, for mixing of immiscible(incapable of

mixing) liquids and to manufacture emulsion for photographic films.

• Welding, local heating and drilling small holes in hard materials.

Uses of ultra sonic waves

• Serve as insect repellants. Strong beam of ultrasonic waves kills bacteria. They are used for sterilisation purposes.

• Cure neuralgic and rheumatic pains.• Surgical instruments vibrating at ultrasonic frequencies are

used in bloodless surgery.• Break gallstones and stones in the kidney.

SONAR – most popular application of ultrasonic wave

• SONAR - SOund, Navigation and Ranging

• Invented by Paul Langevin a French Physcist.

• Invention was inspired by ‘Titanic’ disaster.

• Was developed as a means of tracking enemy submarines during World War II.

• Measure the distance, direction and speed of underwater objects.

Working Of SONAR

• Sonar consists of a transmitter and receiver.

• Transmitter- produces and transmits ultra sonic waves.

• Ultrasonic waves travel through water until they strike an object.

• The waves on striking object get reflected.

• The reflected waves return to SONAR- detected bythe receiver in SONAR.

• Detector converts the ultrasonic waves to electrical signals which are appropriately interpreted.

Topic

Distance calculation using SONAR

• The time interval between transmission and reception is recorded.

• The distance of the object is calculated.

• t - the time elapsed between transmission and reception of the ultrasound signals.

• V - the velocity of sound through water .

• distance d of the object is given by d = Vt/2.• This is called echo-ranging.

Example

• The ultrasound signal sent by Sonar takes 3s to return. • The velocity of sound in water = 1.5 km/s.• The distance travelled by the signal =

= Velocity (v) X time (t)/2.

Velocity X time = (1.5 x 3) = 4.5 km. The distance of the object is (4.5/2) = 2.25 km.

Uses of SONAR

• used to locate submarines and icebergs.• used to determine depth of a sea.

Ultrasound Scanners

• Instrument which uses ultrasonic waves for getting images of internal organs of human body.

• Used in medicine field.• Ultrasonic waves can be directed at a specific area of the

body.• The waves travel through the tissues of a body, the waves get

reflected from a region where there is a change of tissue density.

Ultrasound Scan

Ultrasound Scanners

• The border between two different organs of a body reflect the waves.

• Scanner provides display of images in a static form or a movie picture of the inside of the body.

• Ultrasound images are analyzed to obtain information regarding the internal organs.

Ultrasound Scanners

• Ultrasound – less harmful than X rays• Technique is an invaluable diagnostic tool for examining fluid-

filled organs such as the bladders, kidneys and ovaries. • used to examine the arterial system, the heart, the pancreas,

the urinary tract, the brain and the spinal cord.• ECG – echocardiography- ultrasound is used to examine the

heart.• examination of the foetus during pregnancy to detect

congenial and growth abnormalities.• used to guide surgical procedures.

DOPPLER EFFECT

Doppler effect is the apparent change in frequency of wave motion due to the relative motion between the source and the observer.

Doppler Effect

• Apparent change in pitch or frequency of sound, whenever there is a relative motion between the source of sound and an observer.

• Phenomenon was first investigated by Doppler • called Doppler effect.

Doppler Effect

• Pitch or frequency of the siren of a speeding fire-engine, drops abruptly as it passes the observer.

• Both the observers at rest in the sidewalk hear the same pitch of sound from the fire engine at rest.

Doppler Effect

• Observer towards whom the engine moves feels sound to be of higher frequency while the other observer feels sound to be of lower frequency.

• When the engine moves - waves in front appear to be compressed - hence the observer in front feels the pitch to be higher.

• waves behind the engine appear to be farther apart- and the observer feels pitch lower.

Doppler Effect

• Other examples-• person standing on a railway platform feels a change in pitch

of the whistle of a train in motion.• change in pitch results when a moving observer passes a

stationary sounding horn.

Doppler Effect

• Doppler effect in light:

• The speed of light is so high that only celestial bodies or atomic sources moving at high velocities show pronounced Doppler effect.

Application Of Doppler Effect

• to determine the velocity of submarines.• to detect vehicles crossing speed limit.• used in tracking the artificial satellites.• study of binary stars, saturn rings, galaxies. Doppler effect is

also used to estimate speeds of stars, galaxies, rotation of sun’s disc.

Red Shift

• When a source emits light of particular wavelength and the source is moving away from us, the wavelength appears longer to us. The color of the light is shifted towards the red end of the spectrum.

• This effect is known as a red shift.

EXERCISES

Exercises

• What is the frequency range of audible sound?• The frequency of audible sound is 20Hz to 20,000 Hz.

Exercises

• What are ultrasonic waves?

Ultra sonic Sound is sound which lies above the human audible range .It lies in the frequency of 20kHz to 5 x 105 kHz. Range of wavelengths of ultrasonic sound is from 1.65 cm to about 6 x 10-5 cm. It is similar to sound wave in its propagation and speed but has comparitatively higher energy.Branch of science that deals with ultrasound is called ultrasonics

Exercises

• List any six uses of ultrasonic waves.

Understand physical properties of medium. manufacture alloys , mixing of immiscible(incapable of mixing) liquids

and to manufacture emulsion for photographic films. dry cleaning of clothes to remove grease and dirt. detect cracks and flaws in metal moldings. welding, local heating and drilling small holes in hard materials. serve as insect repellants. Strong beam of ultrasonic waves kills

bacteria. They are used for sterilisation purposes.

Exercises

• What is a Sonar? How does it work?• Sonar stands for SOund, NAvigation and Ranging.It is a device that

uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

• Sonar has a transmitter and detector. The transmitter produces and transmits ultrasonic waves through the water. These waves get reflected back when they strike an object in water. These reflected waves (ultrasonic waves)are captured by the detector.

• The time interval between the transmission and reception (t) is recorded. The velocity of sound through water is V. The distance of the object (d) is calculated.

d = veloicity(v) X time(t) /2

Exercises

• Using Sonar, ultrasonic waves are emitted at the ocean water surface. These waves are reflected by the ocean bottom. If the time interval between the emission of the waves and the detection of the reflected waves, is 3.5 s, find the depth of the ocean.

• Velocity of sound in water = 1.5km/s• Time between transmission and reception = 3.5s• Depth = distance = velocity X time/2 = 1.5 X 3.5/2= 2.6

Exercises

• What is an ultrasound scanner?• Ultrasound scanner is an instrument which uses ultrasonic

waves for getting images of internal organs of human body. It is used in applications in the field of medicine.

Exercises

• Write a note on medical applications of ultrasound waves.• Ultrasonic waves can be directed at a specific area of the body. As the waves

travel through the tissues of a body, the waves get reflected from a region where there is a change of tissue density. Scanner provides display of images in a static form or a movie picture of the inside of the body(baby foetus ). Ultrasounds are widely used in scanning as they are less harmful than X rays. The ultrasound images are analyzed to obtain information regarding the internal organs. This technique is an invaluable diagnostic tool for examining fluid-filled organs such as the bladders, kidneys and ovaries.

• Used in examining heart - echocardiography (ECG)- diagonosis of heart diseases.

• examination of the foetus during pregnancy to detect congenial and growth abnormalities.

• used to guide surgical procedures.

Exercises

• Explain Doppler effect with an example.• Doppler effect is the apparent change in frequency of wave motion due

to the relative motion between the source and the observer.• Pitch or frequency of the siren of a speeding fire-engine, drops abruptly as

it passes the observer. When the engine is moving, waves in front appear to be compressed and hence the observer in front feels the pitch to be higher. The waves behind the engine appear to be farther apart. Hence the other observer feels the pitch to be lower.

Exercises

• Mention three applications of Doppler effect.• Doppler effect in sound can be used to determine the velocity of

submarines.

• Traffic control authorities use Doppler effect to detect vehicles crossing speed limit. Radio waves are used for the purpose. Radio waves are sent in the direction of the speeding vehicle and the reflected waves are received. The change in frequency of the waves is used to determine the speed of the vehicle. The instrument used for the purpose is called Radar gun.

• Doppler effect is used in tracking the artificial satellites.

Exercises

• Write a note on application of Doppler effect in astrophysics.• It is used in the study of binary stars, saturn rings, galaxies. Doppler effect

is also used to estimate speeds of stars, galaxies, rotation of sun’s disc.

• Lines seen in the spectra of galaxies are generally redshifted that is the wavelength is shifted towards the red end of the spectrum. The amount of shift depends on the velocity of the source.

• When a source emits light of particular wavelength and the source is moving away from us, the wavelength appears longer to us. The colour of the light is shifted towards the red end of the spectrum. This effect is known as a red shift.

END OF SLIDE

Speeding of Vehicles

• Instrument is called Radar gun• Radio waves are sent in the direction of the speeding vehicle.• The reflected waves are received.• Change in frequency of the waves is used to determine the

speed of the vehicle.

Flaw Detection

Ultrasonic Welding

Working - Ultrasonic Welding

• The two thermoplastic parts to be assembled are placed together, one on top of the other, in a supportive nest called a fixture.

• A titanium or aluminum component called a horn is brought into contact with the upper plastic part.

• A controlled pressure is applied to the parts, clamping them together against the fixture.

Working - Ultrasonic Welding

• The horn is vibrated vertically 20,000 (20 kHz) or 40,000 (40 kHz) times per second, at distances measured in thousandths of an inch (microns), for a predetermined amount of time called weld time.

• Produces frictional heat at the interface . When the temperature at the joint interface reaches the melting point, plastic melts and flows, and the vibration is stopped. This allows the melted plastic to begin cooling.

Working - Ultrasonic Welding

• Allow it to cool for some time.• Once the melted plastic has solidified, the clamping force is

removed and the horn is retracted. The two plastic parts are now joined as if molded together and are removed from the fixture as one part.

Working - Ultrasonic Welding