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# Reflection of Sound Waves

We are surrounded by a variety of sounds that generate from different sources. But, have you ever thought how sound waves travel? It is surprising how we can listen to cloud thunder which happens far away in the stratosphere. If we look closely, we can surely notice small activities that prove the existence of reflection of sound.

Take two tubes and place them alongside a wall. Now, put a speaker or some sound source close to one end of the tube. You will observe that sound can be heard at the other end of the tube. With the help of this activity, it is proven that surface of the wall does reflect the sound waves. Therefore, we will now try to learn in-depth about the reflection of sound waves and its applications.

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## What is Sound?

Before we directly land on the topic let us understand what is the reflection of sound, let us clear our concept of what does sound exactly signify. It can be defined as auditory sensation or oscillations induced by oscillations in velocity or particle displacement. Do remember that, this displacement is broadcasted in a medium containing internal force. Hence, sound transmits as a mechanical wave via medium like air or water.

### Reflection of Sound

In simple terms, the reflection of sound is actually similar to the reflection of light. How? It also abides different laws of reflection, in which the angle of incidence does prove equal to the angle of reflection. In addition, sound rebounds from the surface of either solid or liquid similar to a billiard ball. For successfully experiencing the reflection of sound, it is important that the surface should be polished or rough, and that too of a considerably large size.

The two laws concerned with sound reflection are as follows:

• The incidence angle will always be equal to the reflection angle.
• Moreover, the incident sound waves, the normal at incidence point and reflected wave, all rest in a common plane.

## Applications Justifying Sound Reflection

### Echo

It is the sound heard when reflections occur from a firm surface, for example, a wall or cliff. Echo is the repetition of sound even after the source has stopped vibrating. This is used by bats as well as dolphins for the detection of obstacles or navigation. Interestingly, SONAR follows the same principle for sound navigation. In SONAR, ultrasonic sound waves are transmitted in all directions through the ship and the signals received are later examined.

### Sound Board

These are basically curved surfaces which are placed in a manner so that the sound source stays at the focus. In a soundboard, the sound waves are uniformly reflected. It can happen in an auditorium or hall, thus improving their quality.

### Hearing Aid

A hearing aid is useful for is people who face difficulty in hearing. In this device, the sound waves are established and reflected into a slimmer area directed to the ear.

### Megaphone

These are horn-shaped tubes which prevent the extension of sound waves through successive reflections. This is achieved through the confinement of sound waves that happen in the tube.

### Stethoscope

You might have seen a stethoscope hanging around your doctorâ€™s neck. This device is used to hear sounds generated from internal organs in the human body. A stethoscope functions on the laws of sound reflection. The sound is received through the chest piece and delivered to the earpieces via multiple reflections occurring through a long tube. By listening to the sound with the help of stethoscope, doctors analyze the situation of an organ.

## Question For You

Q. What are the conditions for an echo to be heard?

Ans. One wouldnâ€™t easily experience echo in a small room. However, this doesnâ€™t mean that sound isnâ€™t reflected in that room, but certain conditions for echo generation arenâ€™t satisfied.

Do remember that, any sound sticks at an individualâ€™s brain for 0.1 seconds. Hence, echo can be heard only if the same sound strikes the individualâ€™s ear after a duration of 0.1 seconds. Therefore, the reflection of sound should reach the brain after a gap of 0.1 seconds.

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