Range of Hearing


Sound II - Concepts
Class - 8th Foundation NTSE Subjects
 
 
Concept Explanation
 

Range of Hearing

Type of Sound: Sound can be of different types- soft, loud, pleasure, unpleasant, musical; audible (can be heard), inaudible (cannot be heard), etc. some sounds may fall into more than one category. For instance, the sound produced when an aeroplane takes off is both loud and unpleasant.

Audible And Inaudible Sounds:

Sometimes a group of neighborhood dogs start barking on their own, while the residents living in the area are left wondering what provoked the dogs to bark. One possible reason could be that the dogs might have heard some unfamiliar high- pitched sound, which the residents did not hear. Our ears are sensitive only to a certain range of frequencies, 20 Hz to 20,000 Hz. We cannot hear sound waves of frequency below 20Hz and above 20,000 Hz. Dogs have the ability to hear very high- pitched sounds, which we cannot. Sound waves of frequency below 20Hz are called infrasonic waves, and those of frequencies above 20,000 Hz are called ultrasonic waves. Human beings cannot hear these sound waves. We also cannot hear sound waves if they are too feeble.

Musical Instruments: We find certain sounds pleasant and associate them with music. In a musical sound, there are a number of frequencies present in a definite ratio or relation to each other.

In stringed instruments like violin, guitar, and sitar, sound is produced by a vibration string. The shrillness or pitch of the sound is altered by changing the length of the vibrating portion of the string.

In wind instruments like trumpet, flute, and harmonica, sound is produced by the vibrating air column inside the instrument.

In percussion instruments like table, drums and dholak sound is produced by a vibrating skin or membrane.

Sample Questions
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Question : 1

A person has the audible range from 20 Hz to  large 20times 10^3 Hz. Find the wavelength corresponding to higher frequency. Take velocity sound as 340 m/s.

Right Option : C
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Question : 2

The frequency of subsonic sound is less than _______________

Right Option : D
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Question : 3

The speed of a body, moving with a speed of 450 m/s, is considered as ____________

Right Option : B
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