Question

What is an echo? Write the conditions to hear an echo.

Answer 1

A repeated sound is caused by the reflection of sound waves from a surface.

Conditions for echo

1. For echo, the time interval between the original sound and reflected sound must be 0.1 s. The sound must go to the obstacle and return to the listener on reflection after 0.1s.
2. The total distance covered by the sound from a source to the obstacle and reflected by the listener must be at least 340 ms^-1 × 0.1s = 34m.
3. So the minimum distance of the obstacle from the source of sound = half of the total distance
   `"34m"/2` = 17m.
4. This distance will change with the temperature of the air.