MP Board · Class 9 · Science · SoundWhat is an echo? State the minimum distance required between the source and obstacle to hear a distinct echo in air at 22 °C.

An echo is the repetition of sound caused by the reflection of sound waves from a distant hard surface like a wall or mountain. To hear a distinct echo, the reflected sound must reach the ear after 0.1 seconds from the original sound. At room temperature (22 °C), the minimum distance required between the source and reflecting surface is 17.2 meters.