Current Affairs 8th Class

Category : 8th Class

Sound

·                     Sound helps us to communicate with each other. It is produced by vibrating objects. In human beings, the vibration of the vocal cords produces sound.

·                     The to and fro or back and forth motion of an object is termed as vibration.

·                     Sound needs a medium to travel, it cannot travel in vacuum.

·                     We hear sound through our ears.

·                     Human ear has three parts ?

·                     The sound enters our ear through outer ear and travels down to eardrum present in the inner ear through a canal. The eardrum senses the vibrations of sound and sends the signals to the brain, in this way we hear the sound.

·                     The frequency of sound is expressed in hertz (Hz). The number of oscillations or vibrations per second is called the frequency of oscillation.

·                     Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. Thus larger the amplitude of vibration louder is the sound. It is expressed in a unit called decibel.

·                     The frequency determines the shrillness or pitch of a sound. Higher the frequency of vibration, the higher is the pitch, and shriller is the sound.

·                     Low frequency vibrations produce low-pitched sound which is loud to hear For example, a drum vibrates with low frequency and thus produces low pitched sound and thus it gives loud sound.

·                     High frequency vibrations produce high-pitched sound which is feeble to hear For example chirping of a bird.

·                     Human ear can detect the sounds of frequencies ranging from 20 to 20,000 Hz. These sounds are called audible.

·                     The sounds above or below this frequency level, are not audible to human ear. Such sounds are called inaudible.

·                     The sounds of frequencies below 20 Hz are called infrasonic sounds.

·                     The sounds of frequencies above 20 Hz are called ultrasonic sounds.

·                     Some animals can hear sounds inaudible to human ears. The animals like dolphins and elephants communicate to each other through the sounds of frequencies below 20 Hz.

·                     The sound which is pleasing to our ears is called musical sound.

·                     Any unpleasant sound is called noise. Such type of sounds in excess lead to noise pollution which may pose various health problems like lack of sleep, hypertension etc. for human beings.

·                     Noise pollution can be minimised by shifting the noise producing industries away from residential areas; running T.V. and radio at low volumes, by minimising the use of crackers/ by planting trees along the roadside and elsewhere.