1. SOUND
Heinrich Rudolph Hertz
(1857 – 1894)

2. Sound
Experiments with Vibrating Tuning Fork
Production of Sound
Propagation of Sound
Sound Waves in Air
Sound Needs Material Medium to Travel
– Bell Jar Experiment
Characteristics of a Sound Wave
Reflection of Sound
Reverberation
Uses of Multiple Reflection
Range of Hearing
Infrasonic and Ultrasonic Sound
Uses of Ultrasonic Sound
SONAR
Created by C. Mani, Deputy Commissioner, KVS RO Gurgaon

3. SOUND
Sound is a form of energy which gives sensation of hearing to us.
Sound is produced due to vibration of a body.
It is a form of mechanical energy.
Sound is produced by:
Vocal cords of human being
Birds and animals
Bell
Vehicles
Musical instruments like guitar, veena, violin, piano, harmonium, flute, shehnai, tabla, drums, cymbals, etc.

4. PRODUCTION OF SOUND Vibrating tuning fork splashes water.
Vibrating tuning fork makes the pendulum bob to oscillate. (Tuning fork vibrations were shown in slow motion.)

5. ‘ ‘
Vibrating blade produces sound.

6. Production of Sound by Musical Instruments
Drum
Flute
Guitar
Veena
Cymbal
Cycle Bell

7. Can sound make a light spot dance?

8. PROPOGATION OF SOUND
Vibrating tuning fork produces a series of compressions and rarefactions in air medium.

9. When an object vibrates and makes sound, the air layers around it also start vibrating in exactly the same way and carry sound waves from the source to our ears.
The air layers (air molecules) vibrate back and forth about their mean positions.
When the layers approach each other they form compressions and when they move away from each other they form rarefactions.
Note that there is no actual movement of air layers from the source of sound to the ears but the sound energy is getting transmitted from one layer to another in succession.
The maximum distance moved by a vibrating air layer on either side of its original position is known as the amplitude of the sound wave.
The number of complete back and forth vibrations of an air layer in one second is known as the frequency of the sound wave.
The distance between two successive compressions or two successive rarefactions is called wavelength.

10. Sound Waves in Air Wavelength Wavelength Rarefaction Compression
Air Layers

11. Sound Waves in Air The sound waves in air are longitudinal waves.
Sound waves in air consist of compressions and rarefactions.
Air layers, though randomly distributed, are almost equally placed from each other.
When the right prong of the tuning fork moves outwards (towards right), it pushes the air layers to the right creating more pressure. Therefore, compressions (regions of high pressure) are formed.
When the right prong of the tuning fork moves inwards (towards left), it creates low pressure. Therefore, rarefactions (regions of low pressure) are formed.
These compressions and rarefactions are passed on to the next layers by the vibrating air layers.
The process is repeated as long as the tuning fork vibrates.
The compressions and rarefactions are alternately formed.
Only the compressions and the rarefactions pass on from one place to other but the air layers (molecules of air) vibrate back and forth about their mean positions.
When these sound waves fall on our ears, the ear drums vibrate accordingly and reproduce the sound.

12. Sound Waves in Air R C Density or Pressure Wavelength (λ) Distance
Average Density or Pressure
Amplitude (A)
Sound Waves in Air

13. Wave shape for a low pitched sound
Wave Disturbance
Time
Wave shape for a low pitched sound
Wave Disturbance
Time
Wave shape for a high pitched sound

14. Wave shape for a soft sound (low intensity)
Wave Disturbance
Time
Wave shape for a soft sound (low intensity)
Wave Disturbance
Time
Wave shape for a louder sound (high intensity)

15. SOUND NEEDS A MATERIAL MEDIUM TO TRAVEL
Bell sound is not heard!
Sound reaches the ears
Vacuum
Air particles
Bell
Vacuum Pump
Air is being evacuated
Air is completely evacuated from the jar. i.e. vacuum is created. Test the bell now!

16. Characteristics of a Sound Wave
Sound does not travel in vacuum.
Sound needs a material medium like solid, liquid or gas to travel and be heard.
Therefore, sound waves are called ‘mechanical waves’.
Characteristics of a Sound Wave
Amplitude (A): The maximum distance moved by a vibrating air layer on either side of its original position is known as the amplitude of the sound wave. Its SI unit is ‘m’.
Wavelength (λ): The distance between two successive compressions or two successive rarefactions is called wavelength. Its SI unit is ‘m’.
3. Time Period (T): The time taken by an air layer to complete one vibration (to and fro motion) is known as the time period of the sound wave Its SI unit is ‘s’.
4. Frequency (n): The number of complete back and forth vibrations of an air layer in one second is known as the frequency of the sound wave Its SI unit is ‘Hertz’.
Relation between Frequency and Time Period:
n = 1 T

17. ii) The speed of sound depends on the temperature of the medium.
The rate at which sound travels in a given medium is called speed of sound.
i) The speed of Sound depends on the nature of material (or medium) through which it travels.
In general, sound travels slowest in gases, faster in liquids and fastest in solids.
Speed of sound in air is 344 m/s at room temperature (20ºC).
Speed of sound in water is 1500 m/s.
Speed of sound in iron is 5130 m/s.
ii) The speed of sound depends on the temperature of the medium.
Speed of sound in air at 0ºC is 332 m/s and at 20ºC, it is 344 m/s.
iii) The speed of sound depends on the humidity of air.
Speed of sound in dry air is less but more in humid air.

18. Speed of Sound in Different Media
S. No.
Medium
Temperature in ºC
Speed of sound in m/s 1
Dry Air
332 2 20
344 3
Hydrogen
1284 4
Water (Distilled)
1498 5
Sea-water
1531 6
Blood 37
1570 7
Copper
3750 8
Aluminium
5100 9
Iron
5130 10
Glass
5170

19. Comparison of Speed of Sound and Light
Sound travels in air at 20 ºC at the speed of 344 m/s.
Light travels at the speed of 300,000,000 m/s. (3 x 108 m/s)
Examples:
In the rainy season, the flash of lightning is seen first and the sound of thunder is heard a little later though both are produced at the same time.
Click the Package to see the effect!
In the game of cricket, the ball is seen to hit the bat first and the sound of hitting is heard a little later.
If a gun is fired from a distance, we see the flash of gun first and the sound of gun shot is heard a little later.
In villages, when clothes are washed by beating them on the stone, the clothes hitting the stone is seen first and the sound of hitting is heard a little later.

20. REFLECTION OF SOUND
Like light, sound gets reflected and obeys the same laws of reflection.

21. Reverberation
A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible.
The repeated reflection that results in this persistence of sound is called reverberation.
In an auditorium or big hall excessive reverberation is highly undesirable.
To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster or draperies. The seat materials are also selected on the basis of their sound absorbing properties.

22. USES OF MULTIPLE REFLECTION OF SOUND
Megaphones, horns, musical instruments such as trumpets and shenais are designed to send in a particular direction with multiple reflections.

23. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.

24. A stethoscope is a medical instrument used for listening to sounds produced within the body, mainly in the heart or lungs.
In stethoscopes the sound of the patient’s heartbeat reaches the doctor’s ears my multiple reflection of sound.

25. The ceilings of concert halls and cinema halls are curved so that sound after reflection reaches all corners of the hall.
Sometimes, a curved soundboard may be placed behind the stage so that the sound, after reflecting from the sound board, spreads evenly across the width of the hall.

26. Curved ceiling of a conference hall
Source of sound
Sound Board

27. Applications of Ultrasound
Range of Hearing
The audible range of sound for human beings is from about 20 Hz to Hz.
Children under the age of five and some animals like dogs can hear upto Hz.
Sounds of frequencies below 20 Hz are called infrasonic sound.
Rhinoceroses, whales and elephants produce infrasonic sound.
Sounds of frequencies above Hz are called ultrasonic sound.
Dolphins, bats, porpoises, moths of certain families and rats can produce ultrasonic sound.
Applications of Ultrasound
Ultrasound is used to clean parts located in hard-to-reach places.
Ultrasound can be used to detect cracks and flaws in metal blocks.
Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’ or ECG.

28. Ultrasound scanner is used for imaging patient’s organs such as the liver, gall bladder, uterus, kidney, etc. This technique is called ‘ultrasonography’. It is also used for examination of the foetus during the pregnancy.
Ultrasound may be employed to break small ‘stones’ formed in the kidneys into fine grains. These grains later get flushed out with urine.
SONAR
SONAR stands for SOund Navigation And Ranging.
SONAR uses ultrasonic waves to measure distance, direction and speed of underwater objects.
SONAR consists of a transmitter and a detector and is installed in a boat or a ship.
The transmitter produces and transmits ultrasonic waves. These waves travel through water and get reflected from the ocean bed.
By measuring the time taken between the sending and receiving of the waves and knowing the speed of sound in water, the distance can be calculated. If the total distance travelled is 2d (to and fro), ‘v’ is the speed of sound in water and ‘t’ is the time taken then 2d = v x t.
The above method is called ‘echo-ranging’. This technique is also used to locate underwater hills, valleys, submarines, icebergs, sunken ship, etc.

29. Distance = 2d
Time = t
Speed of sound = v
d =
v x t 2

30. SONAR PANEL

32. Acknowledgement
Many objects & sounds used in this PPT are copied from various sites.
Reference Material
IX – Science & Technology by NCERT
Science for Ninth Class (Part-1: Physics) by S. Chand