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Chapter – 13
Sound
Sound: Vibrations that travel through the airor another medium and can be heard when they reach a person's or animal's ear.
Musical Sound: The sound which produce a pleasing effect on theear.
Noise: The sounds whichproduce a jarring or unpleasant effect.
Types of Sound:
(i)Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz(20 kHz) are heard by human ear.
(ii) Inaudible Sound: The sounds having frequencies above 20,000 Hz and below20 Hz cannot be heardby the normal human ear.
Low frequency sounds which cannot be heard arecalled infrasonics.
High frequency sounds which cannot be heard arecalled ultrasonics.
Inhuman beings, thevibration of thevocal cords produces sound.
Sound travels through amedium (gas, liquid or solid). Itcannot travel invacuum.
The ear drum senses the vibrations of sound. It sends vibrations to the inner ear. From there, the signal goesto the brain. That is how we hear. Higher the frequency ofvibration, the higher is the pitch, and shriller isthe sound.
Unpleasant sounds are called noise. Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings. Lack of sleep, hypertension (high bloodpressure), anxiety and manymore health disorders may be caused by noise pollution. A person whois exposed toa loud sound continuously may get temporary or even permanent impairment of hearing.
Attempts should be made to minimise noise pollution. Silencing devices must be installed in air craft engines, transport vehicles, industrial machines and homeappliances. Plantation on the roadside and elsewhere canreduce noise pollution.
Amplitude: The maximum extent of vibration ofthe vibrating bodyfrom its meanposition is known as itsamplitude.
Time Period: One complete to and fromovement of thependulum around itsmean position iscalled one oscillation. The time takenby the vibrating particle to complete one oscillation is called timeperiod.
Frequency: The number of vibrations madeby the vibrating body in onesecond is knownas its frequency. The SI unitof frequency is the hertz(Hz).
Characteristics ofSounds:
(i) Loudness: The sensation produced in the ear which enables us to distinguish between a loud and a faint sound. Larger the amplitude of vibration, thelouder is thesound produced. It is proportional to square ofthe amplitude.
(ii)Pitch: Thecharacteristics of sound which distinguishes between a shrill sound and a soft sound. Higher thefrequency of vibration, higher is thepitch and shrillness.
(iii) Quality (Timbre): Characteristic which enables us to distinguish between musical notes emitted by different musical instruments orvoices even though they have thesame pitch and loudness.
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