Exercise 10.4
In a room, the reflected sound reaches the ear s after its production. Will it produce an echo or reverberation? Justify your answer.
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
Reverberation, not an echo.
An echo is heard as a separate sound only if the reflection arrives at least \(\displaystyle 0.1\ \text{s} \) after the original.
Here the gap is \(\displaystyle 0.05\ \text{s} \), and \(\displaystyle 0.05\ \text{s} < 0.1\ \text{s} \), so the brain cannot separate the two — no echo is heard.
Instead the quick multiple reflections from the walls blend with the original and make the sound persist after the source has stopped, which is reverberation.
This is why small rooms never echo: their walls are too close, and the reflections come back too soon.