Page 4 - LN

Velocity = 344m/sec
Speed =distance /time
V= 2x/t
x= v*t/ 2
So, x=344 *0.1/2
=17.2m (minimum distance required to hear an echo)

.
Necessary Conditions for the formation of an Echo.

(i) The minimum distance between the source of sound and the reflecting body
should be 17.2 metres.
(ii) The wavelength of sound should be less than the height of the reflecting body.

(iii) The intensity of sound should be sufficient so that it can be heard after reflection.

(iv) Time gap between the Sound must come back to the person after 0.1 second

Reverberation

If a sound is made in a big hall, the sound waves are reflected repeatedly through
the walls, ceiling and floor of the hall and produce many echoes. The echo time is so
short that many echoes overlap with the original sound. Due to this, the original
sound lasts for a longer time.

(I)It is the persistence of sound after the source has stopped producing it. Due to
reverberation, the sound becomes difficult to hear.

(II)Persistence of sound wave for a long time because of repeated (multiple)
reflections of sound are called reverberation

To avoid this the following are observed

1. Walls are made of sound absorbing materials. Chairs in the halls are also made
up of fabrics that can absorb sound

2. Carpets are put on the floor to absorb sound