We all are familiar with the concept of reflection of sound. We can observe this by a small activity. If we take two tubes and position them against a wall, as shown in the figure below, upon placing a speaker or any other source of sound near one end of the tube, we receive the sound at the end of the other tube. This activity proves that the surface of wall reflects the sound wave. In this section we shall learn more about the reflection of sound and its application in everyday life.
Sound is defined as oscillations or auditory sensation evoked by oscillations in particle displacement or velocity, propagated in a medium with internal force. Sound propagates as a mechanical wave through a medium such as air or water.
Reflections of sound
The reflection of sound is similar to the reflection of light as it follows the laws of reflections, where the angle of incidence is equal to the angle of reflection and the incident sound, the reflected sound and the normal lie in the same plane. Sound bounces off the surface of solid or a liquid like a billiard ball bounces off the sides of the table. In order for reflection of sound to occur, the surface can be either rough or polished and of considerably large size.
Laws of Reflection of Sound
- The angle of incidence is always equal to the angle of reflection.
- The incident sound wave, the reflected wave and the normal at the point of incidence are in the same plane.
Applications of reflection of sound
The sound heard after reflections from a rigid surface such as a cliff or a wall is called echo creating a persistence of sound even after the source of sound has stopped vibrating. Echo is used by bats and dolphins to detect obstacles or navigate. The same principle is used in SONAR, sound navigation and ranging technique, used in oceanographic studies. SONAR is used for the detection and location of unseen underwater objects, such as submerged submarine, sunken ships and ice bergs. In SONAR, ultrasonic waves are sent in all directions from the ship and the received signal is analyzed.
Hearing aid is a device used by people with a difficulty in hearing. Here, the sound waves are received by the hearing aid and are reflected into a narrower area leading to the ear.Megaphone
Megaphones are horn-shaped tubes that prevent the spreading out of sound waves by successive reflections, thus confining them to the air in the tube.
Sound boards are curved surfaces that are placed such that the sound source is at the focus. The sound waves are made to reflect uniformly throughout the hall or an auditorium thus enhancing their quality.
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