Reflection of Sound Sound is a part of our everyday sensory experience.
We hear chirping birds, voices of humans, annoying loud sounds and the soothing sounds
of running water. So how is sound produced, propagated and detected? A good model is the
stethoscope, used to listen to the sounds of the heart and lungs. But how are these
sounds heard? To understand this, we need to know what the reflection of sound is.
When sound travels through a medium, it strikes the surface of another medium and bounces
back to the original medium. This phenomenon is called the Reflection of Sound, which obeys
the Laws of Reflection. The First Law states that the angle of incidence
is equal to the angle of reflection. We can prove this by placing two tubes at certain
angles on a wooden board. If a clock is placed near the end of one of the tube, we can hear
the sound waves through the second tube by adjusting it to get the sound at its maximum.
We can see that the angle of incidence is equal to the angle of reflection. The Second
Law states that the incident wave, the reflected wave, and the normal at the point of incidence,
all lie in the same plane. Sound waves also suffer reflection from large
obstacles. If we stand at a distance from a high wall and clap our hands, we can hear
the same clapping sound after the dying out of the original sound. This is called an echo.
Therefore, for an echo to be heard, the time interval between two sounds must be 0.1 Second.
As sound travels at a speed of 340 meters per second in air, the distance travelled
by sound in 0.1 seconds is 34 meters. Therefore, to hear an echo we need to stand at least
17 meters away from the wall. Now what happens if there are four enclosed walls that are
less than 17 meters away? What we experience here is a reverberation
that is due to multiple reflections of sound from the walls, roof and floor, which follow
so closely behind the original sound that the original sound appears to be prolonged
even when the source of the sound stops. We can thus say that reverberation is the multiple
reflections of sound waves, whereas echo is the single reflection of sound waves.
However, excessive reverberation makes the sound indistinct, which can be a setback in
auditoriums. This can be reduced by using sound absorbing materials like ceilings made
of soft and textured materials and flooring made of acoustic tiles.
Certain technologies make use of the multiple reflections of sound. To name a few, we have
megaphones, hearing aids, sound boards, stethoscopes and the curved ceiling of concert halls.
Now, back to our stethoscope. The stethoscope picks up multiple reflections of sound from
the patient�s body. This causes the flat surface of the diaphragm to vibrate. Each
wave bounces, or reflects, off the inside walls of the rubber tube. In this way, each
wave, in succession reaches the ear tips on the ends of the device, and finally to the
listener’s eardrums, and the doctor interprets the sounds he hears. Things to remember: The property of sound to bounce back from
the surface on which it falls is known as the reflection of sound.
Echo is heard only if the minimum distance between the source of sound and the obstacle
is 17 meters. Reverberation is multiple reflections of sound
after the original sound is produced. The First Law of Reflection states that the
angle of incidence is equal to the angle of reflection
The Second Law of Reflection states that the incident ray, the reflected ray, and normal
at the point of incidence, all lie in the same plane.