Category :
8th Class
Sound
Synopsis
- Sound is a form of energy that produces sensation of hearing in our ears.
- Sound is produced when a body vibrates.
- Sound needs a medium to travel. It cannot travel in vacuum.
- Sound travels faster in solid medium (like wood) as compared to water and air.
- All musical instruments have vibrating parts/which produce sound.
- In human beings, sound is produced by the voice box or the larynx.
- We hear through the vibration of our eardrum, whenever sound reaches our ears.
- The number of oscillations per second is called the frequency of oscillation (f) and is expressed in hertz (Hz). A frquency of 1 Hz is one oscillation per second.
- The time needed to complete one oscillation is called time period (T). Hence, the number of oscillations per unit time is the frequency of wave f = 1 /T.
- The maximum displacement of the wave crest from the central position on either side is called its amplitude.
- We differentiate sounds on the basis of their amplitudes and frequencies.
- A human being can hear sound waves within a range of 20 Hz to 20,000 Hz. Some animals like dogs can hear sounds higher than 20,000 Hz.
- The larger the amplitude of vibration, the louder is the sound.
- Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. The loudness is expressed in a unit called decibel (dB).
- Shrillness or the pitch of a sound depends upon its frequency. Higher the frequency, higher is the pitch and vice-versa.
- Unwanted, unpleasant sound is noise. Loud noise produces noise pollution, which is harmful and may cause hearing impairment.
The velocity of sound in air is approx.\[\text{330}\,\text{m}\,{{\text{s}}^{-1}}\]under standard temperature and pressure conditions. It varies with temperature, pressure, humidity and density of medium.
