Question

An echo is heard only, if the sound after reflection should reach the ear after:

• A. less than $\frac{1}{100}$s
• B. less than $\frac{1}{10}$s
• C. more than $\frac{1}{10}$s
• D. none of these

Answer 1

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

A human ear cannot sense every reflection of sound or echo. For the echo to be heard by a human ear, the sound from the source must reach back to source after reflection after more than 0.1 seconds , that is , more than $1/10s$.

This is due to the fact that a human ear can not differentiate between source sound and echo sound which are produced less than $1/10s$ apart.