Advertisements
Advertisements
Question
When a sound is made from a distance of 18 m, in front of a tall building, it is found to get repeated again. Which phenomenon is associated with this observation? Give a brief explanation of this phenomenon?
Advertisements
Solution
The associated phenomenon is known as Echo. We get echoes because of the reflection of sound. The reflected sound reaches the observer after a time 2d/v, where d is the distance of the reflecting wall from the source. For the human ear. this time must be at least 0.1 seconds to ensure that the reflected sound does not get mixed up with the direct sound. Since the velocity of sound in air is nearly 330 ms−1, we must have
2d/330 > 0.1
or d > 16.5 m
Since the building, in this case, is at a distance of 18 m, we can hear the reflected sound clearly. We thus get a clear echo in this case.
RELATED QUESTIONS
State two factors on which the speed of a wave travelling in a medium depends.
The following diagram shows three ways in which the string of an instrument can vibrate.
(a) which of the diagram shows the principal note?
(b) which has the frequency four times that of the first?
(c) what is the ratio of the frequency of the vibration in (i) and (ii)?
What is the shape of a soundboard kept behind the speaker on the stage of a big hall ?
What is a megaphone ? Name the principle on which a megaphone works.
What is a soundboard ? Explain the working of a soundboard with the help of a labelled diagram.
What are mechanical waves?
What do you understand by the ‘Echolocation system of Dolphins’?
(i) A man stands at a distance of 68 m from a cliff and fires a gun. After what time interval will he hear the echo, if the speed of sound in air is 340 ms−1?
(ii) If the man had been standing at a distance of 12 m from the cliff would he have heard a clear echo?
Write short notes on reflection of sound waves from plane and curved surfaces.
