Reflection of Sound
Subject: Science
Syllabus
Overview
Echo is the reflection of sound by a hill or a large building some distance away. When sound falls on a surface, it is partly reflected and partly absorbed. If there are a number of reflecting surfaces near one another, a series of reflection takes place. Such sound is called reverberation. This note provides information about echo, application of echo, absorption of sound, reverberations and some numerals.
- Note
- Things to remember
- Videos
- Exercise
- Quiz
Reflection of Sound
Like light, the sound reflects and obeys the laws of the reflection. Reflection of sound can be heard in long tunnels, deep wells, deep forest, deep ridges of mountains etc.
Echo is, simply, the reflection of sound by a hill or a large building some distance away. You can hear an echo only from a reflecting surface which is far away. This is because when sound reaches in your ears very quickly, your ears will not be able to distinguish it as a separate sound. In fact, your ears can able to distinguish two sounds as separate sounds only if the second sound wave is received 1/15th of a second or more after the first sound.The minimum distance for an echo to be heard is 17 m approximately.
Application of Echo
The principle of reflection of sound is used in an instrument called SONAR which is used to find the depth of the sea at any time. A SONAR produces ultrasonic pulses which are sent down into the sea from a ship. They are received back after being reflected by the bottom of the sea. SONAR stands for Sound Navigation And Ranging.
The depth of the sea is calculated by measuring the time taken by the echo to be received.
Nature also makes use of the principle of reflection of sound. The bat uses the echo to feel its way through and also to detect its prey. It gives out shrieks of ultrasound which gets reflected from any obstacle and avoids it. If echo comes from an insect, it easily recognises and catches it.
Absorption of sound
When sound falls on a surface, it is partly reflected and partly absorbed. Walls of aroom are good reflectors of sound. Wood, carpets, curtains, clothes and even our bodies absorb sound better and reflect less. In fact, soft surfaces are better absorbers of sound whereas hard surfaces are better reflectors of sound. Porous materials, Soft materials, non-metals, etc. are absorbers of sound.
Reverberations
If there are a number of reflecting surfaces near one another, a series of reflection takes place. Such sound is called reverberation. The reverberation of a thunder is due to thenumber of reflections of sound from clouds, rocks and cliffs, etc. Reflection of sound takes place in a big room, hall or newly constructed room. If the reflecting surface is less than 15m, reverberation distinguishes an echo from the source of a sound. The value of this suitable distance depends on the type of sound produced.
Things to remember
- Echo is simply the reflection of sound by a hill or a large building some distance away hear an echo only from a reflecting surface which is far away.
- The principle of reflection of sound is used in an instrument called SONAR which is used to find the depth of the sea at any time.
- The depth of the sea is calculated by measuring the time taken by the echo to be received.
- It includes every relationship which established among the people.
- There can be more than one community in a society. Community smaller than society.
- It is a network of social relationships which cannot see or touched.
- common interests and common objectives are not necessary for society.
Videos for Reflection of Sound
Reflection of Sound
Reverberation
Questions and Answers
The phenomenon of returning the incident sound wave from a distance more than 17 m is known as echo.
Its two uses are:
i) It is used to find the depth of the sea.
ii) Bats use echo to find its path and prey.
The phenomenon of multiple reflections of sound when a reflector is at a distance less than 17m is known as reverberation. The conditions for the occurrence of echo or reverberation are : i) The sound should be so loud that after reflection also listener must listen.
ii) For an echo distance of reflecting object must be more than 17m and for reverberation, the distance must be less than 17m.
In an empty room, no absorbers are there, so that almost all sound is reflected from the wall and heard louder but materials in the room absorb more sound. Hence, sound will be faint.
Echo is not heard in a small room because to occur an echo reflector should be more than 17m distance and in asmall room, it becomes less than 17m.
We know that a cinema hall is large. The distance between the wall and the source of sound is more than 17m. So, there may be echo and sound may not be clear. So, to avoid it, sound absorbers are kept on the walls of a cinema hall.
| Echo | Reverberation |
| 1. The reflected sound is repeated. | 1. The reflected sound is prolonged. |
| 2. The distance between the sources and sound and reflecting surface should be more than 17m. | 2. The distance between the sources and sound and reflecting surface should be less than 17m. |
Given,
Echo time (t) = 3s
Velocity of sound (v) = 332m/s
Distance (d) = ?
For echo,
v = 2d/t
or, 332 = 2d/3
or, 996/2 = d
∴ d = 448m
Hence, the distance between the man and the hill is 448m.
Given,
Distance (d) = 2km = 2000m
Time (t) = 6sec
Speed (v) = ?
We know, Speed (v) = d/t = 2000/6 = 333.3m/s
Hence, speed of sound is 333.3m/s.
Given,
Echo time (t) = 0.4s
Velocity of sound (v) = 332m/s
Distance (d) = ?
For echo,
v =2d/t
or, 332 = 2d/0.4
or, 132.8/2 = d
∴ d = 66.4m
Hence, the distance between Sita and the surface of water in the well is 66.4m.
Echo time (t) = 5s
Velocity of sound (v) = 330m/s
Distance (d) = ?,
v =d/7 or, 332 = d/5 or, 1650 = d ∴ d = 1650m Hence, the distance of flash from the observer is 1650m.
An instrument called SONAR is used to find the depth of the sea.
Solution,
Distance traveled, s = 660 m/s
Speed (v) = distance traveled / time taken
= 660/ 330
= 2 sec#
So the sound is heard after 2 second.
Solution,
Total distance traveled by sound in going and coming back = 2 sec
Therefore, V = distance traveled/ time taken
Or, s = V x t/ 2
Or, s = 350 x ½
Or, s = 175 m#
Thus, the distance of the hill from the boy is 175 m.
Solution,
t = 1.5 s
v = 14000m/s
h= v x t/2
= 14000 x 1.5 /2
= 1050m#
Thus, the depth of the sea is a 1050m for students.
Quiz
Start
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FAQs
What distance is required for echo to be heard? ›
The total distance between a sound source and the reflector is twice that. So, if the obstacle is at least 17 m away, then after 0.1 second, the reflected sound or the echo is clearly detected. Hence, to hear a clear echo, the minimum distance between the reflecting surface and the observer is 17 m.
What should be the minimum distance between the source and reflecting surface to hear an echo in air? ›To hear an echo, the minimum distance between source of sound and reflecting body is 17m.
How far is a wall if an echo is reflected off it and returns to the source in 3 seconds? ›Distance of reflecting surface from the source s=vt=342×1. 5=513m.
Is it true that the echo is the term used for the sound that is reflected back to its source? ›An echo is a sound that is repeated because the sound waves are reflected back. Sound waves can bounce off smooth, hard objects in the same way as a rubber ball bounces off the ground. Although the direction of the sound changes, the echo sounds the same as the original sound.
What is the least distance for echo? ›Echoes are heard due to the phenomenon of Reflection of sound waves. To hear the echo clearly, the reflecting object must be more than 17.2 m from the sound source for the echo to be heard by a person standing at the source.
Why will an echo not be heard when the distance? ›The echo will not be heard when the distance between the source of sound and the reflecting surface is because the least distance to hear an echo is .
What is the minimum distance required to form an echo in steel? ›Thus, the minimum distance to hear echo is 17.2 m.
Is it possible to produce an echo in a room of length 10 m? ›To hear an echo, there should be at least a distance of 17 m between the source of the sound and the body from which sound is reflected. In small rooms this is not the case, so echoes are not heard.
What is the minimum distance to hear an echo in water when speed is 1500 m s? ›Minimum distance =v×t2 = 1500×0.12=75m.
Can we hear the echo if we are too close to a big hard wall? ›So this means that the minimum distance the obstacle needs to be at to hear an echo is 17 meters. So if the obstacles are closer than 17 meters, we won't hear the echo. And so this explains why we don't hear echoes in our rooms.
Why do we hear echo in mountains? ›
For reflection of sound wave to take place the size of the reflector should be large So a mountain side and deep valleys are good reflector of sound for producing an echo.
What is the minimum distance between the source of sound and the reflector for echo to be heard if the velocity of sound in air is 340 m s? ›So, if the obstacle is at a distance of 17 m at least, the reflected sound or the echo is heard after 0.1 second, distinctly.
What is the full meaning of echo? ›: the repetition of a sound caused by reflection of sound waves. : the sound due to such reflection. : a repetition or imitation of another : reflection.
Is there any difference between echo and reflection of sound explain? ›...
Difference Between Echo and Reverberation.
| Echo | Reverberation |
|---|---|
| It is the reflection of a sound wave off a surface. | It is created by the reflection of sound waves created by the superposition of echoes. |
An echo is a sound caused by the reflection of sound waves from a surface back to the listener. It is the reflection of sound, arriving at the listener some time after the direct sound.
How far away can you hear a human voice? ›The normal intelligible outdoor range of the male human voice in still air is 180 m (590 ft 6.6 in).
Does distance affect echo? ›The farther away the source of a sound is from a listener, the more echoes there are, and the more degraded the depth of amplitude modulation gets.
Why echo can not heard in a small room? ›Beacuse time gap between direct sound and reflected sound too low to be perceptible by human ear. Because small rooms reflect less amount of energy.
Can you hear echoes everywhere? ›we can hear echoes anywhere, where the distance between the source and the point of reflection is sufficient enough.
Can an echo be silent? ›Sometimes we need to be quiet. Shouting Alexa commands while your baby or significant other sleep can cause undesirable results. Thankfully, Alexa has a “whisper mode” so we can do what we need to do quietly without causing utter chaos.
What should be the minimum distance between two buildings? ›
| Wall Condition* | Maximum Building Height above Base Plane or Curb Level, as Applicable (in feet) | |
|---|---|---|
| 25 | 50 | |
| Wall to Wall | 20 | 35 |
| Wall to Window | 30 | 45 |
| Window to Window | 40 | 55 |
What is the distance of the cliff from the person if the speed of the sound, `v` is taken as `346 m//s` ? UPLOAD PHOTO AND GET THE ANSWER NOW! Solution : Here, `t = 5 s, v = 346 m//s, d = (vt)/(2) = d = (346 xx 5)/(2) = 865 m`.
What are the three conditions for echo? ›- The minimum distance between the source of the sound and the reflector should be at least. 17. 2m.
- The size of the reflector must be large, as compared to the wavelength of the incident sound.
- The intensity or loudness of the sound waves must be sufficient.
This is due to the distance sound waves travel and the fact that there is generally less to absorb the waves as they pass across the room. The larger the space and the harder the walls, the more echo you will experience.
What stops an echo in a room? ›- Cover the Floor. Carpets and rugs do more than provide soft padding for your feet. ...
- Cover the Walls and Windows. Wall and window coverings reduce the amount of sound reflecting off window glass and hard wall surfaces. ...
- Fill Rooms with Furnishings. ...
- Install Acoustic Panels.
Sound will echo in an empty room because if there is nothing to stop the sound from reflecting between hard surfaces, such as the walls, windows, ceiling, and floor . Since each surface is not a perfect reflector, some of the sound energy will be absorbed by the surface.
What is the minimum distance required for the formation of echo in water if speed of sound in water is 1450m s? ›What should be the minimum distance between the source of sound and so that the echo is heard distinctly? (Speed of sound in water is 1450 mis between the source of sound and the reflector in water eed of sound in water is 1450 m/s). (Ans: 72.5 m]
Why can you not hear the echo if you stand 10 m away from a wall and shot towards it? ›Echo will not be heard when the distance between the source of sound and the reflecting surface is 10m because the least distance to hear an echo is 17m.
How are echoes used by a ship to find the depth of the water? ›depth finder, also called echo sounder, device used on ships to determine the depth of water by measuring the time it takes a sound (sonic pulse) produced just below the water surface to return, or echo, from the bottom of the body of water.
Why does a man hears an echo if he is too close to a wall? ›(i) The echo must be heard after 0.1s of the transmission of the sound wave otherwise it gets overlapped with the sound and our ears are not able to distinguish between the two. Now, since sound travel approximately at 340m/s therefore it should be able to travel a minimum of 34m before it hits our ears.
What is the maximum distance to hear an echo? ›
The minimum distance for echo to be heard is 17.2 m. But is there a maximum distance for echo to be heard? No, there is no maximum distance to hear an echo.
How do I reduce the echo in my house with high ceilings? ›Utilizing fabric wrapped acoustical panels is your first line of defense for how to reduce echo in a room with high ceilings. They are constructed of acoustical materials and trap enough waves to reduce both echo and reverberation. Place them near eye level for maximum effect.
Why do we hear an echo when we speak loudly among hills? ›The reflection of sound is called echo. Echo is heard only when surfaces are far away. Echo is heard on hills because there is no object to absorb the sound.
Why do we hear two echoes? ›Reflection of sound leads to the formation of echo. When a sound is repeatedly reflected from a number of obstacles, such as two parallel distant buildings or hills, more than one echo can be heard. Was this answer helpful?
What finds an echo in the poets heart? ›Solution : As the drops of rain fall on shingles, they make a tinkling sound. The tinkling sound echoes in the poet's heart.
What is the minimum distance required for a person to hear the echo of his sound? ›To hear an echo, the minimum distance between source of sound and reflecting body is 17m.
What is the minimum distance between a person and a reflective surface for him to hear his own echo? ›Since sound has to travel an equal distance in going up to the reflecting surface and in coming back from the reflecting surface, therefore it must travel nearly 33/2 = 16.5m either way. Thus, to hear the echo clearly in the air, the reflecting surface should be at a minimum distance of 16.5m from the source of sound.
Why must reflecting surface be at least 17 m away for an echo to be heard? ›Since the sound speed is 340 m / s the sound traveling distance is 34 m in 0.1 second. The total distance between a sound source and the reflector is twice that. So, if the obstacle is at least 17 m away, then after 0.1 second, the reflected sound or the echo is clearly detected.
Is echo a real name? ›From a sweet cry to an adorable coo, Echo is a baby girl name of Latin and Greek origin. Meaning “reflected sound,” you might recognize an echo in tunnels, waves, and by skipping tiny pebbles. Besides these beautiful vibrations, the name Echo derives from a nymph who loved Narcissus in Greek mythology.
Why is it called an echo? ›A true echo is a single reflection of the sound source. The word echo derives from the Greek ἠχώ (ēchō), itself from ἦχος (ēchos), "sound". Echo in the Greek folk story is a mountain nymph whose ability to speak was cursed, leaving her able only to repeat the last words spoken to her.
What is the sentence of echo? ›
His voice echoed around the room. The call echoed off the walls of the cave. Their voices echoed back across the water. The protest seemed to echo across the room.
What do you mean by reflection of sound give two example? ›Reflection of Sound Waves – The bouncing back of the sound wave on striking a surface such as a wall, metal sheet, plywood, etc. is called the reflection of the sound wave. Reverberation – If the distance is less than 17 m, then the original sound mixes with the reflected sound.
What is an echo Class 7? ›An echo is a sound caused by the reflection of sound waves from a surface back to the listener. It is the reflection of sound, arriving at the listener sometime after the direct sound.
What is full form of echo? ›What is an echocardiogram? An echocardiogram (echo) uses high frequency sound waves (ultrasound) to make pictures of your heart. The test is also called echocardiography or diagnostic cardiac ultrasound.
What is echo in real life? ›When a sound wave is produced in air, some of it is absorbed after hitting with a reflector while some of the sound wave is reflected back to the listener. This reflected sound is called echo.
What are the three essential conditions for an echo to be heard? ›- The minimum distance between the source of the sound and the reflector should be at least. 17. 2m.
- The size of the reflector must be large, as compared to the wavelength of the incident sound.
- The intensity or loudness of the sound waves must be sufficient.
An echo is an example of wave reflection. Reflection occurs when waves bounce back from a surface they cannot pass through.
What are the two characteristics for an echo to be heard? ›Then we see the important conditions to hear an echo that are The minimum distance between the observer and the obstacle should be 17m in the air. The minimum time gap between the source and the echo should be 0.1 seconds.
How far can a human hear? ›The commonly stated range of human hearing is 20 to 20,000 Hz. Under ideal laboratory conditions, humans can hear sound as low as 12 Hz and as high as 28 kHz, though the threshold increases sharply at 15 kHz in adults, corresponding to the last auditory channel of the cochlea.
What is an example of the echo effect? ›Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound source.