The cause of echo is reflection of sound. When sound waves encounter a smooth and hard surface, such as a wall or cliff, they bounce back towards the source. If the reflected sound reaches the listener’s ears distinctively after the original sound, an echo is heard. The time delay between the original sound and its reflection determines the perception of an echo.
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The cause of echo is primarily [A] reflection of sound. When sound waves encounter a large and hard surface, such as a building, cliff, or canyon wall, they reflect off the surface and return towards the source. If the distance to the reflecting surface is significant enough, the reflected sound reaches the listener’s ears distinctly after the original sound, creating an echo. The perception of an echo depends on the time delay between the direct sound and its reflection.
Absorption of sound (option [C]) reduces echo by absorbing sound waves rather than reflecting them. Refraction of sound (option [B]) involves the bending of sound waves due to changes in temperature or density gradients, but it does not cause echoes directly. The speed of sound (option [D]) affects the timing of echo perception but is not the direct cause of echo itself. Therefore, reflection of sound (option [A]) is correctly identified as the cause of echo.