Sound (ध्वनि)
Sound play an important role in our lives. It helps us to communicate with one another.
" Kind of sensation received by our ears and received by our brain sound is produced by vibrating objects"
Sound is produced by a vibrating body :- When a tightly stretched band is plucked, it vibrates and produced sound. When it stops vibrating, it does not produce any sound.
** Musical instruments are commonly used in many parts of our country. These instruments are simply be written or struck.
Musical sound :- the sound which produce a pleasing effect on the ear.
Noise :- The sound which produce a jarring or unpleasant effect. Unpleasant sound is called noise.
Sound produced by human :- in humans, the sound is produced by the voice box or the larynx.
Voice box is the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air.
** When the lungs Force air through the slit, the vocal cords vibrates producing sound.
** When the vocal cords are tight and thin the type or quality of voice is different from that when they are loose and thick.
Sound needs a medium for propagation :- sound travel through a medium (solid, liquid or gas). It cannot travel in vacuum.
We hear sound through our ears :- The shape of the ear is like a funnel. When sound enter it, it travels down a canal at the end of which there is a thin stretched membrane. It is called eardrum.
** The eardrum is like a stretched rubber sheet. Sound vibration make the eardrum vibrate. The eardrum sends vibration to the inner ear. From there the signal goes to the brain, that is how we hear.
** The eardrum sense the vibrating of sound, it sends the signal to the brain and this process is called hearing.
Amplitude :- the maximum distance of a vibrating or swinging object from its position of rest.
Time period :- one complete and free movement of the pendulum around its mean position is called on oscillation. The time taken by the vibrating particle to complete one oscillation is called time period.
Frequency :- the number of vibrations for oscillation made by a vibrating body in a second. The unit of frequency is hertz (Hz)
Characteristics of sound :-
1. Loudness :- The sensation produced in the ear which enables us to distinguish between a loud and a faint sound. Larger the amplitude of vibration the louder is the sound produced.
2. Pitch :- The characteristics of sound which distinguish between a shrill sound and a soft sound. Higher the frequency of vibration, higher is the pitch.
3. Quality :- Characteristics which enable us to distinguish between a musical notes limited by different musical instruments aur voice even through they have the same pitch and loudness.
Types of sound -
(1) Audible sound :- vibration whose frequency lies between 20 Hz to 20000 Hz(20KHz)
(2) Inaudible sound :- the sound having frequency above 20000 Hz and below 20 Hz cannot be heard by the normal human ear.
Noise pollution :- excessive or unwanted sounds leads to noise pollution. It may pose health problems for human beings
** Plantation on the roadside and elsewhere can reduce noise pollution.
** The loudness of sound expressed in a unit called decibel (dB).
Normal breathing sound - 10dB
Soft whisper sound - 30dB
Normal conversation sound - 60dB
Busy traffic sound - 70dB
Average factory sound - 80dB
** Above 80 dB the noise becomes physically painful.
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