CBSE Class 9 Answered

Dear student,

When sound is incident on a solid or a liquid surfaceit bounces off the surface like light rays. Sound waves also obey the laws of reflection and refraction. For sound waves to reflect, we need extended surface or obstacle of large size. For example, the rolling of thunder is due to successive reflections from clouds and land surfaces.

According to the law of reflection of sound the directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface and the three lie in the same plane.

Some applications of the principle of Reflection of Sound are:

(1) Megaphone, (2) Hearing Board, (3) Sound Boards.

(1) Megaphone

: Megaphone is a horn-shaped tube. The sound waves are prevented from spreading out by successive reflections and are confined to the air in the tube.

(2) Hearing aid

: It is a device used by the people who are hard of hearing. Here the sound waves, which are received by the hearing aid are reflected into a narrower area leading to the ear.

(3) Sound Boards

: Curved surfaces can reflect sound waves. This reflection of sound waves is used in auditorium to spread the waves uniformly throughout the hall. Reflection of sound waves is done by using Sound Boards. The speaker is located at the focus of the sound board.

Bats and dolphins can detect the presence of an obstacle by hearing the echo of the sound produced by them. This process is called sound ranging.One of the most important applications of the reflection of sound is oceanographic studies. For this purpose, we use a system called the SONAR. The SONAR is abbreviated form of Sound Navigation and Ranging.

Hope this helps.

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