1. Sound

2. 10.1 Production of sound by vibrations
The tuning fork vibrates and you hear a sound.
Sounds are made when an object vibrates.
Sounds is a form of energy that produces sense of hearing.

3. 10.2 Transmission of sound in terms of compressions & rarefactions
Longitudinal Wave
wave particles vibrate back and forth along the path that the wave travels.
Compression Wave

4. Compressions
The close together part of the wave
Rarefactions
The spread-out parts of a wave

5. The Loudspeaker The Loudspeaker
The compressions and rarefactions move away from the speaker as sound waves

8. 10.3Human range of audible frequencies

9. How sound reaches to us ?
1. Sound waves are collected by the outer ear (or pinna).
6.The auditory nerve
takes the signals
to the brain.
4. The small bones (ossicles) amplify the vibrations.
2. The waves travel along the ear canal.
3. The waves reach the eardrum and make it vibrate.
5. The cochlea turns these into electrical signals. 9

10. Range of Hearing
Human beings can hear sound frequencies between 20 Hz and 20 KHz.
Sound whose frequency is less than 20 Hz is called infrasonic sound. Animals like dogs, elephants, rhinoceros, whales etc. produce and hear infrasonic sound.
Sound whose frequency is more than Hz is called ultrasonic sound. Animals like dolphins, bats, rats porpoises etc. produce and hear ultrasonic sound.
Bats use reflection of ultrasonic sound waves to detect an obstacle or its prey.

11. Comparing hearing ranges
Which animals hear the lowest and the highest frequencies?
100,000
10,000
1,000
100 10 1
frequency
(Hz)
Frequency low (Hz) high (Hz)
Human
Dog
Bat
Elephant
Mouse
Cat
Dolphin
human
dog
bat
elephant
mouse
dolphin

12. 10.4 Sound need medium to travel
The bell-jar experiment
vacuum
pump on

13. 10.6 Order of magnitude of speed of sound in different medium
The speed at which it travels though a material will therefore depend on how close together the molecules are, and so upon the density of a material - the more tightly packed the molecules, the more quickly vibrations can be transferred from molecule to molecule, i.e. the faster the sound can travel though the material.

14. Speed of sound in different materials
The speed of sound is approximately:
340m/s in air - gas molecules are relatively far apart, and the transfer of vibrations (sound) is relatively slow
1400m/s in water - liquid molecules are much closer together, and transfer of vibrations is much more rapid
6000m/s in steel - solid molecules are even closer together, and transfer of vibrations is even more rapid

15. Sound in different materials
Sound needs a substance through which to travel because it travels by making particles vibrate.
Which state of matter does sound travel fastest through?
Sound waves travel fastest through solids.
The particles in a solid are closer together than in a gas, and more tightly bound than in a liquid. This means vibrations are more easily passed from particle to particle, and so sound travels faster. 15

16. Sound waves in different materials

18. 10.7 Technical terminology of Sound
Amplitude-
maximum distance the particles in a wave vibrate from their rest positions.
Frequency
number of waves produced in a given time

19. Sound Wave

20. The louder the sound, the greater the amplitude.
What is the difference between the sound wave of a quiet sound and a loud sound?
quiet sound
loud sound
The loud sound has taller waves.
The louder the sound, the greater the amplitude.

21. What is the difference between the sound wave of a low pitch sound and a high pitch sound?
The high pitch sound has a shorter wavelength,
so more waves are visible. It has higher frequency waves.

22. Frequency  Pitch
Amplitude  Loudness
Loudness
The loudness of a sound increases with the amplitude of the sound wave.
loud
quiet

23. The pitch increases with frequency.
low pitch
high pitch .

24. Match the description to the oscilloscope pattern:B C D
1. Low-pitched sound, very loud D
2. Loud, high-pitched sound C
3. Medium sound with medium pitch B
4. Quiet, high-pitched sound A

25. Echo
If we shout or clap near a reflecting surface like tall building or a mountain, we hear the same sound again. This sound which we hear is called echo. It is caused due to the reflection of sound.
To hear an echo clearly, the time interval between the original sound and the echo must be at least 0.1 s.
Since the speed of sound in air is 344 m/s, the distance travelled by sound in 0.I s = 344 m/s x 0.1 s = m
So to hear an echo clearly, the minimum distance of the reflecting surface should be half this distance, that is 17.2 m.
Reverberation
Echoes may be heard more than once due to repeated or multiple reflections of sound from several reflecting surfaces. This causes persistence of sound called reverberation.
In big halls or auditoriums to reduce reverberation, the roofs and walls are covered by sound absorbing materials like compressed fiber boards, rough plaster or draperies.

26. Quizenia

27. Credits
Jonathan watts/science photo gallery
Rex features
Science photos/Alamy