REFLECTION OF SOUND

Published on: February 13, 2024

Reflection of Sound

Like light, sound also bounces off a solid or liquid. Sound follows the law of the reflection of light. When the incident wave, reflected wave, and normal to the reflecting surface lie on the same plane, the incident wave and reflected wave make equal angles with the normal to the reflecting surface.

Do an activity.

Activity

Take two identical pipes. Arrange them on a table near a wall, as shown in the figure. Keep a clock near the open end of one of the pipes.

Adjust the position of the pipes to hear the sound of the clock from the free end of the other pipe.

Measure the angle of incidence and reflection.

The angle of incidence and the angle of reflection will be equal.


 

Echo

Echo: If we make a sound near a suitable reflecting object at an appropriate distance, we will hear the same sound again a little later. This sound that we hear is called an echo.

Persistence of Audibility: The sensation of hearing a sound persists in the human brain for about 0.1 seconds. This is known as the persistence of audibility.

 

Minimum Distance to the Obstacle to Hear an Echo:

To hear a distinct echo, the time interval between hearing the original sound and the reflected one must be at least 0.1 s.

If the speed of the sound is 344 m/s, it will travel 34.4m in 0.1 s.

Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance, which is 17.2 m. This distance will change with the temperature of the air.

Echo is heard multiple times because sound reflects multiple times. The roaring of thunder is due to multiple reflections of sound from clouds, land, etc.

 

Reverberation

The repeated reflection that results in the persistence of sound is called reverberation.

Methods to Reduce Reverberation:

1. Cover the roof and walls of the auditorium with sound-absorbing materials like compressed fiberboard, rough plasters, or draperies.

2. Seat materials are also selected based on their sound-absorbing properties.

3. Make the floor rough.

 

1. Megaphones, loudspeakers, or horns

These are designed to send sound in a particular direction, not in all directions. If so, the sound can travel a longer distance. The conical opening makes the sound spread in the desired direction.

2. Stethoscope

A stethoscope is a medical instrument used to hear the sounds produced within the body. In stethoscopes, the sound of the patient’s heartbeat is collected by the chestpiece of the stethoscope. The sound reaches the ear tips of the instrument through multiple reflections within the tube.

3. Curved ceilings

The ceilings of some concrete halls, conference halls, and cinema halls are curved so that sound after multiple reflections reaches all corners of the hall. Some soundboards may be placed behind the stage, which makes the reflected sound spread evenly across the width of the hall.

 

Frequently Asked Questions

 

Q1. What is the reflection of sound?

Ans: The reflection of sound is a phenomenon where sound waves encounter a surface and bounce back. This occurs when sound waves strike a boundary that does not allow them to pass through easily.

Q2. What is an echo?

Ans: An echo is a reflected sound wave that arrives at the listener's ears after bouncing off a surface, resulting in the perception of a repeated or reflected sound.

Q3. How is an echo different from the original sound?

Ans: An echo is a delayed and attenuated replication of the original sound. It occurs when sound waves reflect off surfaces, creating a distinct auditory effect.

Q4. What is reverberation?

Ans: Reverberation is the persistent reflection of sound waves in an enclosed space, causing a continuous and prolonged decay of sound after the original sound source has stopped.

Q5. How is reverberation different from an echo?

Ans: While both involve the reflection of sound, reverberation is a continuous and overlapping series of reflections, creating a prolonged decay of sound, whereas an echo is a distinct repetition of the original sound.