Reflection of sound waves and echoes

Reflection of Sound Waves

Sound is reflected or bounced back like a ball when it hit any object.

Laws of reflection of sound

The angle of incidence is equal to the angle reflected for a sound. The direction of the incident sound, direction of reflected sound, and the normal all lie in the same plane.

Uses of Multiple reflections of sound

a.Musical Instruments

Musical instruments such as Trumpets are designed in a particular design where the sound is not spread.

In these instruments, a tube is followed by a conical opening to guide the sound to the audience. Some of the instruments that use this method are Nadhaswaram, shehnai, loudspeaker, horns, megaphones, etc.

Trumpets produces sound by reflection of sound waves
Trumpets By This file was contributed to Wikimedia Commons by Toledo-Lucas County Public Library as part of a cooperation project. The donation was facilitated by the Digital Public Library of America, via its partner Ohio Digital Network.Source record: identifier: c8a7388ca20497adf863257a4a0cfa38, Public Domain,


It is a medical instrument used to listen to sounds produced from the body. The sounds produced from the body reach the doctor’s ears after multiple reflections in the connecting tube.

Stethoscope works by reflection of sound
Stethoscope works by reflection of sounds By this version: Sonarpulse. origenal:Huji – modified version made by myself of image:Stethoscope-2.jpg, Public Domain,


Noise is a bad sound or unpleasant sound. A loudness of more than 120 dB (Decibel) and higher cause pain to the ear.

Continued exposure of 120 dB or more causes hearing problems or permanent hearing loss. Temporary hearing loss can be experienced with being exposed to a loud band for a long time or a loud bang for a short time.

A hearing can be avoided in workplaces by wearing ear protectors.


When sound-wave hit on reflecting surfaces such as tall buildings, mountains, etc, it will the reflection the same, This reflection is called an Echo.

The sound sensation persists or continues in our brain for about 0.1s.

Condition for Echo:

  • To hear a distinct echo, the time interval between the original and the echo must be at least 0.1s.
  • The sound must hit the reflecting surface or object and return to the listener after 0.1 s.
  • The total distance of sound traveled from the reflecting surface to the sound source should be at least 340 ms-1 x 0.1 s = 34m at 25-degree Celcius.

Thus for hearing echoes, the minimum distance must be 17m. This distance will be changed with the temperature of the air. Echoes may be heard multiple times due to multiple reflections.

The huge thunder sound is due to multiple reflections from the clouds at different heights and the land.

Dolphin Waves

Dolphin uses sound waves to navigate and to determine the shape, size, speed of moving objects in the waters. Dolphin uses a technique known as echolocation. By this technique, the dolphin produces high-frequency waves (click).

When this wave gets reflection from any object, the dolphins receive by their lower jaw and foreheads. These body parts of dolphins have enormous fatty tissue, that acts as a sensor and channelizes to its ear. That makes the dolphin see objects using sound for its navigation and food.

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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