1. Transmission of sound through a medium
The Nature
of Sound Waves
Sound Waves
Propagation of Waves
Transmission of sound through a medium
Transmission of sound through a medium
Propagation of Waves
Sound Waves by
Rifki Irawan

2. Sound Waves Sound Waves
Sound is a wave which is created by vibrating objects and propagated through a medium from one location to another .
Sound waves are produced by the vibration of some objects.
Sound wave is a disturbance which is transported through a medium via the mechanism of particle-to-particle interaction.
Sound wave is characterized as a mechanical wave.

3. Propagation of Waves Propagation of Waves
Sound waves are produced when a vibrating object alternately pushes and pulls on the air adjacent to it, thus causing small but rapid changes in the air pressure.
prongs are stationary
layers of air

4. prongs move outwards
compressed
When the prongs move outwards, layers of air are pushed close together so that compression of the air particles is formed.
This disturbance of air layers is then passed from particle to particle, causing the compression to move outwards.

5. prongs move inwards
rarefied
When the prongs move inwards, the air layers are pulled apart, causing a decompression or rarefaction of the air particles.
When the prongs move outwards again, the second compression forces the previous rarefaction away.

6. rarefaction
prongs keep on vibrating
( low pressure ) λ
compression
direction of sound waves
( high pressure )
A series of compression (high pressure regions) and rarefaction (low pressure regions) move away from the tunning fork at the speed of sound.
However, the air particles themselves just vibrate back and forth from their original positions.

7. Transmission of Sound through a Medium
Sound waves need a medium for transmission.
Sound cannot propagate through a vacuum medium.
The speed of sound differs in gasses, liquids, and solids. This is due to the differences in the strength of the interatomic forces and closeness of the atoms in the three states.

8. Comparison of the speed of sound in different media at 25o C
Compressions and rarefactions propagate faster in denser media.
Sound travels faster in liquids than in gasses and fastest in solids.
Medium
Speed (m∙s-1)
Air
346
Hydrogen
1340
Water
1500
Flint glasses
4540
Iron (steel)
5200
Granite
5400
Comparison of the speed of sound in different media at 25o C

11. Echoes Echoes happen if the reflected sound is heard
after an interval of silence.
Example :
A boy standing 68 m from a high wall claps his hands and hears an echo 0.4 s later. Find the speed of sound in air.
Total distance travelled by sound = 2 x 68 m
Time taken = 0.4 s
Speed of sound = distance travelled / time taken
= ( 2 x 68) / 0.4
= 340 m s -1

12. Sound is heard when the compressions and rarefactions reach the ear and set the eardrum vibrating.
The human ear can hear sounds of frequencies in the range of 20 Hz to Hz. This frequency range is reffered to as the range of audible frequency.
Assignment :
Group work
Make a display about the common sounds with an estimate of their intensity and decibel level, infrasonic, and ultrasonic
Display must be completed in two weeks

13. Thank you for watching
- end of presentation -