Class 9 Physics Sound Echo

Echo

 

When we shout near a mountain, we will hear the same sound again and again with small time interval gaps. This is called an echo. Echoes may be heard more than once due to successive or multiple reflections

 

The sensation of any sound persist in our ear for about 0.1 s, which means that to hear a clear echo, the reflected sound must be atleast 0.1 seconds after the original sound.

  • The sensation of any sound persist in our ear for about 1 s
  • The speed of sound in air at 22 degress is 344m/s
  • Therefore, Distance = Speed * Time = 344m/s * 0.1 s = 34.4m
  • That is the full distance ie from the source to the wall and back to the source. So, half the distance ie 2 metres is the minimum distance of the obstacle to hear a clear echo.

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