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An echo is produced due to which property of sound?
A. Refraction
B. Reflection
C. Absorption
D. Dispersion
Correct Answer Is Option = Reflection
Notes / Explanation
An echo is produced due to the property of sound known as reflection, which is the bouncing back of sound waves when they strike a hard surface. Sound travels through the air in the form of waves, and when these waves meet an obstacle such as a wall, a cliff, a large building or the surface of a mountain, they do not simply pass through it or disappear, but instead a portion of the sound bounces back in the same way that a ball bounces back when it is thrown against a hard surface. When this reflected sound returns to the listener after a short delay, it is heard as a repetition of the original sound, and this repeated sound is what is called an echo. For an echo to be heard clearly and separately from the original sound, certain conditions must be met. The reflecting surface must be large enough and hard enough to bounce the sound back effectively, and it must be located at a sufficient distance from the source of the sound so that the reflected sound takes a noticeable amount of time to return. If the surface is too close, the reflected sound returns so quickly that it merges with the original sound and cannot be distinguished as a separate echo. This is why echoes are commonly experienced in large open spaces, near tall cliffs, in empty halls and in valleys surrounded by mountains, where there is enough distance for the delay to be noticeable. The phenomenon of the reflection of sound has many important practical applications. One of the most significant is the use of reflected sound waves to measure distances and to detect objects that cannot be seen directly. Ships and submarines use devices that send out sound waves and listen for the reflections in order to measure the depth of the water and to detect objects beneath the surface. Similar principles are used in medical equipment that produces images of the inside of the body using sound waves, and in various instruments used in science and industry. The study of the reflection of sound therefore has both everyday and practical importance. For PPSC and other competitive examinations, the key points to remember are that an echo is produced due to the reflection of sound, that the reflecting surface must be hard and at a sufficient distance, and that the reflection of sound is used in technologies for measuring depth and detecting objects.
