Application of Echo | JEE Important Topic

Suppose you are standing at the edge of a cliff and you shout your name, and it seems like the mountains answer back to you with your name. This phenomenon is called echo. This also happens when you shout in a large hall room. This phenomenon mainly happens due to the reflection of sound waves with the change of propagation medium. This is a basic property of sound waves and there are many real-life and biological applications of echo that we will discuss here. 

What Is Echo?

Now we know the physical phenomena of echo. Let us define echo in physics: When a sound divides from its unique sound and repeats itself due to reflection, the reflected sound is called an echo. When we speak, we throw sound in a particular direction (forward or away from us), then it returns back to us, becomes noticeable in our brain, and we say our voices get echoed. 

How is Echo Formed?

We know that sound waves only travel through some medium. When the density of the medium increases, a few sound waves transmit through the medium of different densities while some get reflected towards the source, producing an echo.

Sound wave forming echo

You can also observe the echo of a sound wave with this small set-up:

Take a big rope and tie it to a hard surface or wall. Now, start moving the other end of the rope such that you make sine waves on the rope. You will observe the rope reflecting back from the hard surface. Thus, you can observe the phenomenon by hand.

Waves generated using a rope

Now we would explain how echoes are formed in large hall rooms or on the cliff of a mountain. So, we know that sound waves get reflected when the traversing medium’s density gets higher. So, sound waves get reflected in a small room too, but we don't hear the echo. Sound waves travel at a velocity of 343 $\dfrac{m}{s}$ in air. If the distance from the nearest wall is “$l$”, the sound wave needs to travel $2l$ distance and it will require time $\dfrac{2l}{343}$ seconds. And our brain needs 0.1 seconds to distinguish between two different sounds. For small rooms, $\dfrac{2l}{343} < < 0.1$ as the “$l$” is small. That’s why it happens but we can not notice.

Echo in a small room

Application of Echo Sound

There are a lot of real-life uses of an echo or reflection of sound waves. Here we are discussing some of the important ones.

1. Measuring Depth and Height

Measuring heights or depths is a pretty basic application of an echo. Suppose there is a well with a depth ‘h’ metre and we have a source and receiver of sound waves, and we have a stopwatch to measure the time. Now we send sound waves from the source in the well and they come back to the receiver, and we measure the time amount in the stopwatch.

So, the sound wave has to travel (h-(-h))=2h 

Now time required by it is,

$t=\dfrac{2h}{v}$ 

v=velocity of sound waves

Now we can measure “t” in the stopwatch, so we can get h using the above equation.

Similarly, we can calculate the height.

Measuring depth of a well

2. Measuring Distance

As we have seen earlier, by knowing the velocity, we can find out any distance by measuring the time it takes for the wave to return. Submarines use this principle to measure the distance in deep seawater. SONAR (Sound Navigation and Ranging) is used for the purpose, where a particular frequency of sound waves is released and the distance is calculated.

SONAR in Submarine

3. Animals Using Echo

There are few animals, especially mammals with weak optical power, that rely on echo to hunt prey, self-defence and find mates. Bats and dolphins use a self-built biological SONAR system to hunt prey. They emit ultrasonic waves if they get hit by their prey. They know their position and can hunt them. They can even guess the physical measurements of the prey via this method. Even a bat can produce and hear a sound of about 100000 Hz.

4. Medical Purpose

Ultrasonic imaging is a common use of echo in medical fields nowadays. It is the safest way of getting images of your internal organs. An integrated source and a receiver are held on the organ to be scanned that emits high-frequency sonic waves that get reflected by the internal organs, thus producing images of internal organs. We can modulate frequency according to the organ and person for a better image.

Conclusion

From a mountain cliff to your classrooms, echoes happen everywhere, all the time around you, whether you notice it or not. It is a very interesting property of a wave to change its velocity in different media, thus generating interesting phenomena. It has so many applications, so you can expect questions from its real-life applications in the JEE paper. It is basically a theory-based topic, and one can perform the mathematical side accordingly. We suggest you solve some problems on this topic before your JEE paper.