Question

An echo of the sound produced can be heard only if it reaches our ear after

• A. 1/15th of a second
• B. 1/13th of a second
• C. 1/10th of a second
• D. 1/5th of a second

Answer 1

The correct option is C

1/10th of a second

1. An echo is the repetition of the original sound heard after the sound is reflected from a distant, dense, and rigid object (such as a high building, cliff, etc.).
2. The human ear can hear two sounds separately only if they reach the ear after an interval of 1/10th of a second.
3. This is a natural feature of the human ear.
4. Therefore the reflected sound which can be heard distinctly (after a lapse of at least 0.1 sec) from the original sound is called an echo.

Hence, (C) is the correct answer.