SOUND | Class 8 Science Notes

Echo and its applications

An echo is the reflected sound that is heard after the original sound. For an echo to be heard clearly, the reflecting surface must be at a sufficient distance from the source so that the time interval between the original sound and the echo is at least 0.1 seconds. Since sound travels at approximately 340 m/s in air, the reflecting surface must be at least 17 meters away (because sound has to travel to the surface and back, total 34 meters). Echoes have practical applications in sonar, which is used by ships and submarines to detect underwater objects by sending sound waves and receiving their echoes. Bats use echoes to navigate and locate prey in the dark, a process called echolocation. Ultrasound imaging in medicine also uses reflected sound waves to create images of internal body parts. Echoes can also be a disturbance in auditoriums or halls, so soundproofing and acoustic design are important to control echoes for clear sound.

📊 Diagram: Diagram showing a person shouting towards a cliff and hearing the echo after the sound reflects from the cliff. The path of the sound wave to the cliff and back is shown with arrows.

🧪 Activity: Activity: Clap near a large wall and measure the time between the clap and the echo using a stopwatch. Calculate the distance of the wall using the speed of sound formula.

🔗 Connection: This section on echo applications connects to the next section on the range of hearing in humans and animals.