State two applications of echo.

Echo is a phenomenon where sound waves are reflected off surfaces and heard again after a delay. It has several practical applications, including:

Sonar Systems: Echo is used in sonar (Sound Navigation and Ranging) systems to determine the depth of bodies of water and to locate underwater objects. In a sonar system, a sound pulse is emitted, and the time it takes for the sound waves to bounce off an underwater object and return as an echo is measured. By knowing the speed of sound in water and the time delay, the distance to the object can be calculated.

Acoustic Testing and Imaging: Echo is also used in acoustic testing and imaging, such as in medical ultrasound and industrial non-destructive testing. In medical ultrasound, high-frequency sound waves are emitted into the body, and the echoes produced by bouncing off internal structures are used to create images of organs and tissues. In industrial settings, echoes can be used to inspect the integrity of materials and structures, helping to detect flaws or defects without damaging the object being tested.