Reflection and Refraction of Sound
When sound travels from one medium to another medium, it strikes the surface of the medium and bounces or return back in some other direction, this phenomenon of returning back of sound is called the reflection of sound.
Echo and reverberation are the products of reflection of sound.
Echo:
The repetition of sound, which is reflected from walls of large room or distant surface is called echo.
Conditions required for echo:
- The distance between the source of sound and reflecting body should be more than 17m
- The reflector should be hard and of large area.
Reverberation:
If the distance between the source of sound and reflecting body is less than 17m, original sound and reflected sound mix and the sound is prolonged. This process is known as reverberation. It is heard in an empty room or newly built building.
Noise and Music
A sound which produces an unpleasant and jarring effect on the ear is called noise. The sound which produces a pleasing sensation on the ear is called musical sound. Musical sound is characterized by a regular, continuous vibration while a noise does not have any of these characteristics.
Differences between Musical sound and Noise
| Noise | Musical sound |
| It produces an unpleasant effect on the ears. | It produces a pleasant effect on the ears. |
| It has abrupt, harsh and discontinuous sound. | It has regularity and rhythm. |
| Changes in amplitude may be sudden. | Changes in amplitude are not sudden. |
Sound pollution
Noise pollution or noise disturbance is the disturbing or excessive noise that may harm the activity or balance of human or animal life.
Effects of sound pollution
- It increases blood pressure and sugar level in blood.
- It may make people deaf and can cause ear problems.
- Communication based on sound is disturbed in noisy places.
- It makes people tired, nausea etc.
Remedy of Sound Pollution
- Cinema halls and industries should be established far from residential areas.
- Use of private vehicles should be reduced and public transport should be used.
- Afforestation should be done in living and working areas.
- Sound absorbing materials such as glass, wool, carpet, etc. should be used.
- Unnecessary use of horn of vehicles should be avoided and silencer should be used in vehicles.
Refraction of sound
Refraction is the process of bending of waves when they pass from one medium to another where their speed is changed or different. Refraction of sound is not important as the refraction of light but the refraction of sound is an interesting phenomenon in sound. As we know that sound in heard clearer at night than in day- time. This is due to the refraction of the sound wave. During the day- time, the temperature of the air near the land is more than the temperature of the air above it. As we go up, the layer of air behave as a denser medium and hence the ray of sound diverges upwards from the source and as a result less sound is heard by the listener. This phenomenon is just opposite during the night. The layer of air near the land or ground behave as a denser medium and the upper layer as a rarer medium. Here, the ray diverging upwards from the source is refracted away from the normal and undergoes total internal reflection and travels downwards. As a result, sound is heard more distinct and clear by the listener.
Things to remember
- The repetition of sound, which is reflected from walls of large room or distant surface is called echo.
- If the distance between the source of sound and reflecting body is less than 17m, original sound and reflected sound mix and the sound is prolonged. This process is known as reverberation.
- A sound which produces an unpleasant and jarring effect on the ear is called noise.
- The sound which produces a pleasing sensation on the ear is called musical sound.
- 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 and Refraction of Sound
Echo Sounding (Finding Depth)
Reflection of Sound: Echo
Reflection of Sound: Reverberation
Sound echoes and dolphins
Questions and Answers
The repetition of sound produced due to the reflection from walls of a large room, hill, mountain, etc. is called an echo.
The required conditions for echo are as follows:
- The distance between the sources and sound and reflecting surface should be more than 17m.
- The loudness of the sound should be sufficient enough so that it can be heard after reflection.
When the reflected sound mix with the original sound and the sound is prolonged, then this phenomenon is called reverberation.
The conditions for reverberation are as follows:
- The distance between the sources and sound and reflecting surface should be less than 17m.
- There should be number of reflecting surfaces close to one another.
| Echo | Reverberation |
| The reflected sound is repeated. | The reflected sound is prolonged. |
| The distance between the sources and sound and reflecting surface should be more than 17m. | The distance between the sources and sound and reflecting surface should be less than 17m. |
In big auditorium or cinema hall, the reverberation is easily occurred and it creates the sound confusion. To avoid this, walls of auditorium and cinema hall are covered with sound absorbing materials.
For echo, the distance between the sources of sound and reflecting surface should be more than 17m. Hence, it is not heard in a small room.
In a furnished room, the furniture and other materials absorb sound a lot and in a newly constructed room, almost sound is reflected and reverberation takes place. So, reverberation is experienced more in newly constructed room than in a furnished room.
The total internal reflection of sound occurs at night but it is impossible at day time. So, sound is heard more distinct at night than at day time.
| Musical sound | Noise |
| 1. It produces a pleasing effect on our ears. | 1. It produces an unpleasing effect in our ears. |
| 2. It has regular and rhythmic sound. | 2. It has harsh, irregular and discontinuous sound. |
The sound which is not pleasant to our ears is called noise. The pollution caused by noise is called sound pollution. The barking of dogs, sound from vehicles, etc. are the examples of sound pollution.
We can reduce it by following ways:
- Controlling the production of unnecessary sound from the sources
- Use of sound absorbing materials
- Using noisy sources away from residential area
Any four effects of sound pollution are as follows:
- It may make people deaf and can cause ear problems.
- It makes difficult to talk.
- It makes people tired and distressed.
- It makes people irritated and short tempered.
Solution:
Here,
The time to strike the bottom of sea and return back is considerably equal.
∴ Time = 3/2 = 1.5 s
Velocity of sound in water (v) = 1500m/s
Depth of sea (d) = ?
We have,
d = v x t
= 1500 x 1.5
= 2250 m
Hence, the depth of the sea is 2250m.
Quiz
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FAQs
What is the repeated reflection of sound from the walls of a big hall that results in persistence of sound called? ›
A sound created in a big hall will persist by repeated reflection from walls until it is reduced to a value where it is no longer audible. The repeated reflection of sound that results in persistence of sound is called reverberation.
When a sound is reflected from a distant object and echo is produced? ›Answer: An echo is heard when the time interval between the reflected sound and the original sound is at least 0.1 second.
What are repeated echoes of sound called? ›Reverberation, on the other hand, happens when sound persists as a result of repeated reflection or scattering after the sound source has stopped. So while an echo is a distinct sound, reverberated sounds are difficult to hear clearly because the reflections keep repeating.
What is an echo when is an echo heard? ›If the time interval between original sound and reflected sound is more than 101s, then the original sound and the reflected sound can be clearly heard. This reflected sound is known as echo.
When you face and shout against the wall sound is reflected the reflected sound is known as <UNK>? ›When we produce a sound wave and it strikes an obstacle, it comes back to us after reflection, this reflected sound wave is called echo. For example, when we shout or clap near a suitable reflecting objects such as a tall building or a mountain, we will hear the same sound again a little later.
When you face and shout against the wall sound is reflected This reflected sound is known as? ›Echoes. 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.
What is reverberation and echo? ›Echo is a single reflection of a sound wave off a surface. Reverberation is the sound or the pattern created by the superposition of such echoes.
What do we call the process of detecting distance through reflecting sound? ›sonar, (from “sound navigation ranging”), technique for detecting and determining the distance and direction of underwater objects by acoustic means. Sound waves emitted by or reflected from the object are detected by sonar apparatus and analyzed for the information they contain.
What is the process for locating distant or invisible objects by sound waves reflected back the emitter from t he objects? ›echolocation, a physiological process for locating distant or invisible objects (such as prey) by means of sound waves reflected back to the emitter (such as a bat) by the objects. Echolocation is used for orientation, obstacle avoidance, food procurement, and social interactions.
What is called reverberation? ›Reverberation is the persistence of sound after it has been stopped due to multiple reflections from surfaces such as furniture, people, air, etc., within a closed surface. These reflections build up with each reflection and decay gradually as they are absorbed by the surfaces of objects in the enclosed space.
What is reverberation and reverberation time? ›
Reverberation reduces when the reflections hit surfaces that can absorb sound such as curtains, chairs and even people. The reverberation time of a room or space is defined as the time it takes for sound to decay by 60dB.
What is the use of echo? ›Echoes are used by bats, dolphins and fisherman to detect an object / obstruction. They are also used in SONAR (Sound navigation and ranging) and RADAR(Radio detection and ranging) to detect an obstacle.
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 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 called echo? ›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.
What do you called to the behavior of sound wave when reflected sound is scattered at many angles? ›In results, the reflected sound is scattered at many angles. We call this phenomenon as acoustic diffusion.
What is the reason for hearing noises in the distance while standing near a body of water? ›This phenomena is due to the refraction of sound waves and temperature plays a key role. Sound wave speed is dependent on air temperature.
Which phenomenon explains why sound is heard at longer distance at night than in day? ›Temperature inversion is the reason why sounds can be heard much more clearly over longer distances at night than during the day—an effect often incorrectly attributed to the psychological result of nighttime quiet.
What are laws of reflection of sound give three applications of reflection of sound? ›Just like the reflection of light, the reflection of sound is similar as it follows the laws of reflections, where the angle of reflection is equal to the angle of incidence and the reflected sound, the incident sound, and the normal sound belong in the same plane.
What is another name for reflection of sound? ›Echo – Repetition of sound caused by the reflection of the sound wave is called an echo.
Which of the following can be the example of reflection of sound waves? ›
Sound boards: Curved surfaces can reflect sound waves. This reflection of sound waves is used in auditorium to spread the waves uniformly throughout the hall. Reflection of sound waves is done by using Sound Boards.
What is echo with example? ›An echo meaning is that it is a kind of sound that occurs due to the reflection of sound waves. The sound waves produced from a certain source bounce off from smooth and hard objects. It is just like a tennis ball that bounces off a wall.
What is reverberation Class 9 answer? ›The NCERT class 9 Science definition of reverberation states the following: The persistence of sound caused by the multiple sound reflections even after the source has stopped is called reverberation.
What is the difference between echo and reverberation class 9th? ›Echo is formed in both open and closed spaces. Reverberation occurs in closed spaces with multiple reflecting objects. The echos can be used to calculate distance of the object. The distance of a reflecting object cannot be determined by the reverberation, since the travel time is too small.
What type of the sensor is used for measuring the distance by using the theory of light? ›Laser Distance Sensors: LIDAR
LiDAR, in short for Light Detection and Ranging, can be considered as a laser distance sensor. It measures the range of targets through light waves from a laser instead of radio or sound waves.
Stethoscope works on principle of multiple reflections of sound.
How do you find the distance of an echo? ›If we know the speed of sound and the time it takes for the echo to be detected, we can use the equation: Speed = to work out distances. Distance = speed x time.
Is the process of locating objects by emitting sound and then interpreting the sound waves that are reflected from these objects? ›Echolocation is the process of locating objects by emitting sounds and interpreting the sound waves that are reflected back.
What is the method of detecting and locating underwater objects using reflected sound waves? ›Sonar uses sound waves to 'see' in the water.
NOAA scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the seafloor such as shipwrecks, and map the seafloor itself. There are two types of sonar—active and passive.
Answer and Explanation: A reflected sound waves is called an echo.
What is reverberation and noise? ›
Reverberation noise is produced when a sound source stops within an enclosed space. Sound waves continue to reflect off the ceiling, walls and floor surfaces until they eventually die out. These reflected sound waves are known as reverberation.
How does reverberation occur Class 8? ›Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air.
What is reverberation with examples? ›Reverberation : “Due to repeated reflections at the reflecting surface reflector is less than 17 metres from original sound the sound gets prolonged This effect is known as reverberation.” Example : 1. Speaking in a large empty room. 2. Clapping in tombs like TajMahal.
What is reverberation time Mcq? ›The time for which sound continues to be heard (due to persistence) after the source has stopped producing the sound is called reverberation time .
What is reverberation in a room? ›When a sound is made in a room it travels outwards in all directions. As soon as it hits a hard surface such as a wall, floor or ceiling, it bounces straight back off, the sound then passes back and forth between the surfaces, creating reverberation. This sounds similar to an echo, but shorter.
What is echo and its types? ›An echocardiogram is an ultrasound test that checks the structure and function of your heart. An echo can diagnose a range of conditions including cardiomyopathy and valve disease. There are several types of echo tests, including transthoracic and transesophageal.
How an echo is formed? ›This phenomenon is called an echo, which has its origins in the Greek ekho, meaning “sound.” An echo happens when a sound wave reflects off a surface, such as the water at the bottom of a well, and the sound is repeated back to you.
Why do we hear echo? ›When we produce a sound wave and it strikes an obstacle, it comes back to us after reflection, this reflected sound wave is called echo. For example, when we shout or clap near a suitable reflecting objects such as a tall building or a mountain, we will hear the same sound again a little later.
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.
Is echo a boy name? ›Echo Origin and Meaning
The name Echo is both a boy's name and a girl's name meaning "echo". Although this is traditionally seen as a female name, via the classical mythological nymph who pined away for Narcissus until all that remalined of her was a disembodied voice--it can also be used for boys.
What is echo time for Class 7? ›
An echo is the repetition of sound that results as a reflection from a surface. We cannot hear an echo unless the reflecting surface is beyond a specified distance from the source of the sound. The minimum distance required to hear an echo is 17.2 metres. The sensation of sound persists for 0.1 second.
What are the two types of echo? ›- Transesophageal echocardiogram.
- Transthoracic echocardiogram.
There are three types of echocardiography: transthoracic echocardiogram (TTE), transesophageal echocardiogram (TEE) and intracardiac echocardiogram (ICE). A transthoracicn echocardiogram takes images within the body from the skin's surface, without devices entering the body.
What is echo of sound? ›An echo is a repetition or a partial repetition of a sound due to REFLECTION. REVERBERATION is also reflected sound, but in this case, separate repetitions of the original sound are not distinguishable.
Why is it called echo? ›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.
What is the reflection of sound called? ›Echo is a reflection of sound that arrives at the listener with a delay after the direct sound. Moreover, the delay is proportional to the distance of the reflecting surface from the source and the listener.
What is the reflection of sound waves called? ›Echo – Repetition of sound caused by the reflection of the sound wave is called an echo.
What are the results of sound reflected from a wall? ›Reflection of sound waves off of surfaces can lead to one of two phenomena - an echo or a reverberation. A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less.
Is the repetition of sound that is reflected from walls in a large room or from a distant surface? ›Echo: The repetition of sound, which is reflected from walls of large room or distant surface is called echo.
What is difference between echo and reverberation? ›Echo is formed in both open and closed spaces. Reverberation occurs in closed spaces with multiple reflecting objects. The echos can be used to calculate distance of the object. The distance of a reflecting object cannot be determined by the reverberation, since the travel time is too small.
What do you mean by an echo? ›
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.
Is echo reflection of sound? ›In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the listener.
How is an echo formed? ›This phenomenon is called an echo, which has its origins in the Greek ekho, meaning “sound.” An echo happens when a sound wave reflects off a surface, such as the water at the bottom of a well, and the sound is repeated back to you.
What is diffraction of sound? ›Diffraction. DIFFRACTION. The phenomenon in SOUND PROPAGATION whereby a SOUND WAVE moves around an object whose dimensions are smaller than or about equal to the WAVELENGTH of the sound.
When a sound wave hits a wall and echoes back this is an example of what? ›Reflection. An echo is an example of wave reflection. Reflection occurs when waves bounce back from a barrier they cannot pass through.
Which of the following can be the examples of reflection of sound waves? ›Reflection of sound is used to measure the speed and distance of underwater objects. This method is called SONAR. Working of a stethoscope – the sound of patient's heartbeat reaches the doctor's ear through multiple reflections of sound.
What property of sound forms an echo? ›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.
What do you mean by reverberation and reverberation time and echo? ›Reverberation is the persistence of sound after the sound source has been stopped. It results from a large number of reflected waves which can be perceived by the brain as a continuous sound. On the other hand, an echo occurs when a pulse of sound can be heard twice.