Question

An echo is heard when the time interval betweeen the original sound and reflected sound is _____.

• A. more than $\frac{1}{10}s$.
• B. less than $\frac{1}{10}s$.
• C. less than $\frac{1}{150}s$.
• D. more than $\frac{1}{150}$ s.

Answer 1

The correct option is A more than $\frac{1}{10}s$.

Echo is defined as the reflection of sound, arriving at the listener some time after the direct sound. As the sensation of sound persists in our brain for about $0.1s$, to hear a distinct echo, the time interval between the original sound and the reflected one must be atleast $0.1s$.