Question

a short note on echo.

Answer 1

Repetition of sound by a reflection of sound waves from a surface is called echo.

Answer 2

The repetition of sound caused by reflection of sound waves from an obstacle is known as an echo. The sensation of sound persists in our brain for about 0.1 s. To hear a distinct echo, the time interval between the original and reflected sound must be at least 0.1 s. If we take the speed of sound to be 344 m/s at a given temperature, say at 22°C in air, then the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344 m/s) × 0.1 s = 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be 17.2 m.