Question

The echo will be heard if the original sound reflected by an obstacle reaches our ears after

• A. 10 s
• B. 5 s
• C. 1 s
• D. 0.1 s

Answer 1

The correct option is D 0.1 s

When sound waves travel in a medium, it gets reflected from the obstacle and we hear the same sound produced even after some time. This reflected sound is known as echo.
Human ear can hear an echo if the reflected sound reaches the ear after at least $0.1s$. If the reflected sound reaches the human ear in less than $0.1s$, then we cannot hear the echo.