## 07 December 2011

### IX Physics key concept Ch. Sound

1. Sound is a wave that is created by vibrating objects and propagated through a medium from one location to another.

2. A disturbance that travels through a medium, transporting energy from one location to another location is called wave. The medium is simply the material through which the disturbance is moving; it can be thought of as a series of interacting particles.

3. In our body Vocal cord is vibrating body that produce sound wave.

4. The sound wave is transported from one location to another by means of particle-to-particle interaction like air particles in air.

5. Air particles interact continuously throughout the entire medium that causes disturbance to its nearest neighbours till sound reach to listener.

6. A sound wave is a disturbance that is travel through a medium via the mechanism of particle-to-particle interaction. Hence sound wave is characterized as a mechanical wave.

7. Longitudinal waves are waves in which the particles of the medium propagate is in a direction that is parallel to the direction of energy transport.

8. Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave move.

9. The back and forth vibration of the string causes individual air molecules These back and forth vibrations are imparted to adjacent neighbours by particle-to-particle interaction. Other surrounding particles begin to move rightward and leftward, thus sending a wave to the right.

10. Air molecules are moving in a direction that is parallel to the direction that the wave moves, the sound wave is referred to as a longitudinal wave

11. In longitudinal wave, the compressions are regions of high air pressure while the rarefactions are regions of low air pressure

12. The wavelength is commonly measured as the distance from one compression to the next adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.

13. A sound wave consists of a repeating pattern of high-pressure and low-pressure regions moving through a medium, it is sometimes called pressure wave.

14. The particles of the medium through which the sound moves when vibrating a back and forth motion is called its frequency.

15. If a particle of air vibrate 100 times in 2 seconds, then the frequency of the wave would be 50 vibrations per second. Unit for frequency is the Hertz (abbreviated Hz).

16. 1 Hertz = 1 vibration/second

17. Human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz

18. Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound

19. Any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound.

20. The sensation of a frequency is known as the pitch of a sound.

21. The time taken for one oscillation is called time period.

22. The amount of energy that is transported through a given area of the medium per unit of time is known as the intensity of the sound wave. Intensity is the energy/time/area or power/area.

23. Units for the intensity of a sound wave are Watts/meter2.

24. The speed of a sound wave in air at a temperature of 20 degrees Celsius= 343 m/s

25. The maximum displacement of an oscillating body from its central position is called its amplitude

26. The loudness of sound depends upon the amplitude of vibration. If the amplitude is less the sound is feeble. If the amplitude is more the sound is loud. The unit of loudness is called decibel (dB).

27. The pitch of sound depends upon the frequency of vibration. If the frequency is less the sound has low pitch. Eg :- sound of a drum, sound of an adult etc. If the frequency is more the sound has a high pitch. Eg :- sound of a whistle, sound of a baby etc.

28. The mathematical relationship between speed, frequency and wavelength is Speed = Wavelength x Frequency

29. The Human Ear consists of three basic parts - the outer ear, the middle ear, and the inner ear.

30. The outer ear consists of an earflap and an approximately 2-cm long ear canal through sound waves reaches the eardrum

31. The middle ear is an air-filled cavity that consists of an eardrum and three tiny, interconnected bones - the hammer, anvil, and stirrup.

33. The eardrum amplify sounds with frequencies of approximately 3000 Hz

34. The movements of the eardrum will set the hammer, anvil, and stirrup into motion at the same frequency of the sound wave.

35. The inner ear consists of a cochlea, the semicircular canals, and the auditory nerve.

36. Cochlea converts sound wave frequency into electrical impulses.

37. The auditory nerve transfer electrical impulses towards the brain.

38. The brain is capable of interpreting the qualities of the sound upon reception of these electric nerve impulses.

39. Noise :- Unpleasant sounds are called noise. It is produced by irregular vibrations. Eg :- If all the students in a classroom speak together, a noise is produced. Sounds produced by horns of busses and trucks.

40. Musical sound :- Sound which is pleasing to the ears is called musical sound. It is produced by regular vibrations. Eg :- Sounds produced by musical instruments. Sound of a person singing a song.