How Do Echoes Occur? Understanding Sound Reflection in Daily Life
You must have tried to shout your name out loud in the empty school building and heard the name calling you back. When you visit the Ajanta and Ellora caves in Maharashtra and call out your name, it comes back at you. This phenomenon is called echo. These echoes are produced due to the bouncing of sound on solid surfaces.
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.
Echo
Sound Reflection
Sound is produced due to vibrations from an object. It can be due to beating an instrument or an object or from the voicebox of animals.
The speed of sound is 343 m/s.
The direction of the sound changes after it bounces off a surface. But interestingly, the echo is exactly the same as the original sound.
Echoes are heard in enclosed spaces with hard and tough walls such as wells, caves, or large auditoriums.
The sounds may not always get reflected when the sound hits a soft surface like a cloth, cushion, or rubber.
The sound gets absorbed in those surfaces, and hence echoes don’t form.
Sound waves are vibrations produced by various objects and animals.
The light gets reflected on shiny surfaces, and the reflection of sound is very similar to it.
Just the reflecting surfaces are hard and solid in case of sound.
For the proper reflection of sound, the surface needs to be large and can be either rough or polished.
The sound waves also follow laws similar to the laws of reflection of light.
Uses of Echo in Daily Lives
The stethoscope uses the principle of reflection of sound. The thin film vibrates by the sound of the heartbeat and that vibration through the tubes to the earpiece makes us hear the heartbeat clearly.
Sonar is used to find objects and fishes under the sea.
High-frequency sound waves are released under the sea and when hit any object and reflect back the time required by the sound waves to return measures the distance.
The Reflection of Sound Waves
Examples of Echo
A very common example of echo is what happens when we shout our names in a well or in mountains.
Dolphins also use sound waves to navigate their way.
The stethoscope that doctors use to listen to our heartbeats uses the principle of reflection of sound. The thin film vibrates by the sound of the heartbeat, and that vibration is reflected through the tubes to the earpiece making us hear the heartbeat clearly.
Sonar is a device that produces high-frequency sound waves under the sea water and when they hit any object and reflect back the time required by the sound waves to return and measure the distance.
Summary
In the case of an echo, the direction of sound waves might change, but the echo will sound exactly the same as the original sound. Bats fly in the night and release some special kind of sound waves that hit a surface and echo back allowing them to fly away from obstacles. The calls from an average bat can reach up to 130 decibels.
It is interesting to know that some animal sounds do not produce any echo and it's still not clear why such as the dogs barking and ducks quacking.
FAQs on What Are Echoes? Definition, Facts & Examples for Students
1. What is an echo in Physics, and how is it produced?
An echo is the repetition of a sound that a listener hears after the original sound has ceased. It is produced when sound waves travel from a source, strike a hard, distant surface like a cliff or a large wall, and are reflected back to the listener's ear. For the echo to be heard as a separate sound, there must be a sufficient time delay between the original sound and the reflected sound.
2. What are the essential conditions for hearing a distinct echo?
To hear a distinct echo, two primary conditions must be met:
The time interval between the original sound and the reflected sound must be at least 0.1 seconds. This is because the human brain perceives any two sounds occurring within this interval as a single sound.
The minimum distance between the sound source and the reflecting surface must be 17.2 metres in the air (at 22°C). This distance ensures the sound has enough space to travel to the reflector and back in at least 0.1 seconds.
3. Can you provide some real-world examples of echoes?
Echoes are commonly experienced in various environments. For example, if you shout towards a distant mountain or cliff in an open area, you will hear your voice repeated. Another common example is the sound produced when clapping your hands in a large, empty hall or at the top of a well. The sound reflects off the walls or the water surface, creating a clear echo.
4. How is the principle of echo used to measure the distance of underwater objects?
The principle of echo is used in a technology called SONAR (Sound Navigation and Ranging). A ship equipped with SONAR transmits ultrasonic sound waves into the water. These waves travel down, reflect off an underwater object (like the seabed or a submarine), and return to the ship as an echo. By measuring the total time taken for this round trip and knowing the speed of sound in water, the distance to the object can be accurately calculated.
5. Why don't we hear echoes in a small, furnished room?
We don't hear a distinct echo in a small, furnished room for two main reasons. Firstly, the distance to the walls is much less than the required minimum of 17.2 metres. This means the reflected sound returns in less than 0.1 seconds and overlaps with the original sound, so our brain cannot distinguish it as a separate sound. Secondly, soft furnishings like carpets, curtains, and sofas are good absorbers of sound. They absorb most of the sound energy, preventing strong reflections from occurring.
6. What is the main difference between an echo and reverberation?
The main difference lies in the timing and clarity of the reflected sound. An echo is a single, clear, and distinct repetition of a sound due to reflection from a single, distant surface. In contrast, reverberation is the persistence of sound caused by multiple, continuous, and overlapping reflections from various surfaces in a closed space. Reverberation sounds like a prolonged, garbled sound rather than a clean repetition.
7. How can unwanted echoes be reduced in large spaces like auditoriums?
Unwanted echoes and excessive reverberation in auditoriums can make speech and music sound unclear. To reduce them, sound-absorbing materials are used. These include:
Installing thick carpets on the floor.
Using heavy curtains over doors and windows.
Covering walls and ceilings with sound-absorbent materials like fibreboard or acoustic panels.
Having seats with cushioned surfaces that absorb sound.
8. How do animals like bats and dolphins use echoes to 'see'?
Bats and dolphins use a remarkable biological process called echolocation. They emit high-frequency sound pulses and listen for the echoes that bounce back from objects around them. By interpreting the time delay, direction, and characteristics of these echoes, they can form a mental 'map' of their surroundings. This allows them to navigate, locate prey, and avoid obstacles with incredible precision, even in complete darkness or murky water.
