Sound Archives

What is Echo and Sonar

December 18, 2020December 18, 2020 by Veerendra

What Is Echo

The sound returning back towards the source after suffering reflection from a distance obstacle (a wall, a row of building etc.) is called an echo.
When the sound is reflected repeatedly from a number of obstacles, more than one echoes, called multiple echoes are heard. Multiple echoes may be heard one after the other when sound gets repeatedly reflected from distant high rise buildings or hills. The rolling of thunder is an example of multiple echo formation.
The two sounds–one direct and the other echo, can be heard distinctly provided the distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him without interfering with the direct sound. Since the sensation of sound persists for 1/10 second after it is produced, the echo can be heard distinctly only if it reaches at least 1/10 second after the original sound is produced.

Minimum distance between the observer and the obstacle for echo to be heard:
Let
Distance between the observer and the obstacle = d
Speed of sound (in the medium) = v
Time after which echo is heard = t
\( \text{Then, }t=\frac{2d}{v}\text{ or }d=\frac{vt}{2} \)
We know
Speed of sound in air at 25ºC = 343 ms^-1
For an echo to be heard distinctly,
t ≥ 0.1 s
\( \text{Then, }d\ge \frac{343m{{s}^{-1}}\times 0.1s}{2} \)
or d ≥ 17.2 m
Thus, the minimum distance (in air at 25ºC) between the observer and the obstacle for the echo to be heard clearly should be 17.2 m.
The speed of sound increases with a rise in temperature. Therefore, the minimum distance in air between the observer and the obstacle for an echo to be heard clearly at temperatures higher than 25ºC is more than 17.2 m. In rooms having walls less than 17.2 m away from each other, no echo can be heard.

People also ask

How does the sonar work?

The word ‘SONAR’ stands for Sound Navigation and Ranging.

(A) Principle of Sonar
Sonar is an apparatus which is used to find the depth of a sea or to locate the under water things like shoals of fish, enemy submarines etc. Sonar works by sending short bursts of ultrasonic sound from a ship down into sea water and then gets echo produced by the reflection of ultrasonic sound from under-water objects like bottom of sea, shoal of fish, a submarine.

(B) Working of Sonar
Working-of-Sonar
(i) A transmitter (for emitting ultrasonic waves) and (ii) a receiver (for detecting ultrasonic waves). Now suppose a sonar device is attached to the under-side of a ship and we want to measure the depth of sea (below the ship). To do this the transmitter of sonar is made to emit a pulse of ultrasonic sound with a very high frequency of about 50,000 hertz. This pulse of ultrasonic sound travels down in the sea-water towards the bottom of the sea. When the ultrasonic sound pulse strikes the bottom of the sea, it is reflected back to the ship in the form of an echo. This echo produces and electrical signal in the receiver part of the sonar device. The sonar device measures the time taken by the ultrasonic sound pulse to travel from the ship to the bottom of the sea and back to the ship. Half of this time gives the time taken by the ultrasonic to travel from the ship to the bottom of the sea.
d = Depth of sea
v = Velocity of sound in sea water
t = time recorded by the recorder
\(v=\frac{2d}{t}\)

Reason For Using Ultrasonic Waves In Sonar

Ultrasonic waves have a very high frequency due to which they can penetrate deep in sea water without being absorbed.
Ultra sonic waves cannot be confused with the noise, such as the voice of engines of ship. It is because the ultrasonic waves are not perceived by human ear.

Echo And Sonar Example Problems With Solutions

Example 1. A girl hears the echo of his own voice from a distance hill after 3 second. The speed of sound in air is 340 m/s. What is the distance of the hill from the girl ?
Solution: Let d be the distance of the hill from the girl. Total distance travelled by the sound in going and coming back = 2d
Now,
\( v=\frac{\text{Total}\,\text{distance}\,\text{travelled}}{\text{Time}\,\text{taken}}=\frac{\text{2d}}{\text{t}} \)
\( \Rightarrow 340=\frac{2\times d}{3} \)
⇒ d = 510 m

Example 2. The ultrasonic waves take 4 seconds to travel from the ship to the bottom of the sea and back to the ship. What is the depth of the sea ? (Speed of sound in water = 1500 m/s.)
Solution: The time taken by the ultrasonic sound waves to travel from the ship to the sea-bed and back to the ship is 4 seconds. So, the time taken by the ultrasonic sound to travel from the ship to sea-bed will be half of this time, which is 4/2 = 2 seconds. This means that the sound takes 2 seconds to travel from the ship to the bottom of the sea
\( \text{Now, Speed}=\frac{\text{distance}}{\text{Time}} \)
\( 1500=\frac{\text{Distance}}{2} \)
And, Distance = 1500 × 2m = 3000m

Example 3. A submarine emits a sonar pulse which returns from the underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 ms^-1, how far away is the cliff ?
Solution: Given: Speed of sonar pulse, V = 1531 ms^-1, Time interval of return journey of the pulse,
t = 1.02s
Let the distance of the underwater cliff be S.
For distance S of the cliff, the pulse travels a total distance of 2S in return journey.
From relation, distance = speed × time
2S = vt
\( \text{We have, }S=\frac{vt}{2} \)
\( S=\frac{1531m{{s}^{-1}}\times 1.02s}{2} \)
S = 780.8 m

Example 4. An ultrasonic ruler is used to determine the depth of a seabed. A pulse of sound is generated and travels to the seabed before reflecting back. The time taken by the pulse to travel to the seabed and back is 0.28 seconds. If the speed of sound in the water is 1500 m s^-1, calculate the depth of the seabed.
Solution:
Let the depth of the seabed be h m.
The distance travelled by the pulse to the seabed and back = 2h m
2h = v x t
= 1500 x 0.28 = 420 m
Therefore, h = 210 m
Hence, the depth of the seabed is 210 m.

Example 5. A boy shouts towards a mountain and hears his echo 4.5 seconds later.

If the mountain is 765 m from the boy, calculate the speed of sound in air.
Solution:
Let the speed of sound in air be v m s^-1.
The distance travelled by the sound to the mountain and back = 2d
2d = 2 x 765
= 1530 m
2d = v x t
1530 = v x 4.5
Therefore,
v = 1530/4.5
= 340 m s^-1
Hence, the speed of sound in air is 340 m s^-1.

Example 6. A radar transmits a signal towards an aeroplane. The velocity of the signal is 3.0 x 10⁸ m s^-1. After 3.6 x 10^-3s, the radar detects the reflected signal. What is the distance of the aeroplane from the radar?
Solution: 2d = v x t
= 3.0 x 10⁸ x 3.6 x 10^-3
= 1.08 x 10⁶ m
Therefore,
d= 5.4 x 105 m

Classification Of Wave Motion

December 18, 2020December 18, 2020 by Veerendra

Classification Of Wave Motion

On the Bases of Necessity of Medium Required

MECHANICAL WAVES
The wave which propagates only in a material medium are called elastic or mechanical waves.
Example: Sound waves, Water waves (ripples), Waves on stretched strings, Earthquake waves and the Shock waves produced by a supersonic aircraft are mechanical (or elastic) waves.

ELECTROMAGNETIC WAVES
Wave which do not require any material medium for their propagation are called electromagnetic waves.
Example: Light waves, Radio waves, Television waves, and X-rays are electromagnetic waves. Thus, Light waves, Radio and Television waves, and X-rays can also travel through vaccum.

Difference between mechanical waves & electromagnetic waves

	Mechanical waves	Electromagnetic waves
1.	Mechanical waves need a material medium for their propagation. These waves cannot travel through vacuum.	Electromagnetic waves do not need any material medium for their propagation. These waves can travel through vacuum.
2.	Speed of mechanical waves are low and depends upon the source and the medium through which they travel.	(EMW) a electromagnetic waves travel with the speed of light (3 × 10⁸ m/s) in vaccum. The speed of an electromagnetic wave in any material medium is less than that in vaccum.
3.	Mechanical waves are due to the vibrations of the particles of the medium.	(EMW) a electromagnetic waves are not due to vibration of medium particles
4.	Mechanical waves may be longitudinal or transverse waves.	Electromagnetic are transverse waves.
5.	Example: Sound waves, water waves, string waves are mechanical waves.	Examples: Light waves, radio and TV waves, and X-rays are electromagneti

TRANSVERSE WAVES On the Basis of mode of Vibration of the Particle

A wave in which the particles of the medium oscillate about their mean position in a direction perpendicular to the direction of propagation of the wave is called a transverse wave.
Transverse waves can travel through solids and over the surface of liquids, but not through gases.

Examples: Following are the examples of transverse waves

The water waves (ripples) produced on the surface of water is transverse waves. In water waves, the molecules of water move up and down from their mean positions.
A pulse on a slinky when it is given a jerk is a transverse wave.
All electromagnetic waves, e.g., light waves, radio waves etc., are transverse waves.
The waves produced in a stretched string when plucked are transverse waves. When a string of sitar (a musical instrument) or guitar is plucked, transverse waves are produced in the string.

Graphical Representation:
Displacement-distance-graph-for-a-transverse-waves
(a) Crest: The highest point on the hump in a transverse wave is called a crest. Thus, the point of maximum positive displacement on a transverse wave is called a crest.
(b) Trough: The lowest point on the depression in a transverse wave is called a trough. Thus, the point of maximum negative displacement on a transverse wave is called a trough.

LONGITUDINAL WAVES
A wave in which the particle of the medium oscillate (vibrate) to and fro about their mean position in the direction of propagation of the wave is called a longitudinal wave.
Longitudinal waves can be produced in any medium, viz., in solids, liquids and in gases.
Example:
(i) Sound waves are longitudinal waves.
(ii) The waves produced in a spring (slinky) by compressing a small portion of it and releasing are longitudinal waves.

Graphical Representation:
Displacement-distance-graph-for-a-transverse-waves-1
(a) Compression: The part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.
(b) Rarefaction: The part of a longitudinal wave in which the density of the particles of the medium is lesser than the normal density is called a rarefaction.

What is the difference between longitudinal and transverse waves?

	Longitudinal	Transverse waves
1	In a longitudinal wave the particles of the medium oscillate along the direction of propagation of the wave.	In a transverse wave, the particles of the medium oscillate in a direction perpendicular to the direction of propagation of the wave
2	Longitudinal waves can propagate through solids, liquids, as well as gases.	Transverse waves can propagate through solids, and over the surface of liquids, but not through gases.
3	Longitudinal waves consist of compression and rarefactions.	Transverse waves consist of crests and troughs.

Transverse Waves and Longitudinal Waves Experiment

Aim: To study transverse waves and longitudinal waves using a slinky spring.
Material: Ribbon
Apparatus: Slinky spring
Method:

Classification Of Wave Motion 1

1. A slinky spring is placed on the floor. One end of it is tied to the leg of a table.
2. A short length of ribbon is tied to any part of the spring between the two ends.
3. A set of transverse waves is produced by vibrating the spring at right angles with it as shown in Figure The movement of the ribbon is observed.
4. A set of longitudinal waves is produced by vibrating the spring in a to-and-fro direction as shown in Figure The movement of the ribbon is observed.

Observations:

In step 3, the ribbon is displaced in an up-and-down motion which is perpendicular with the direction of the propagation of the waves.
In step 4, the ribbon is displaced in a to-and-fro motion which is parallel with the direction of the propagation of the waves.

Discussion:

The ribbon tied to the slinky spring represents the particles of the medium of the waves.
Step 3 shows that any point on the spring is displaced in an up-and-down motion which is perpendicular with the direction of the propagation of the waves.
Step 4 shows that any point on the spring is displaced in a to-and-fro motion which is parallel with the direction of the propagation of the waves.

Conclusions:

For transverse waves, the particles of the medium move in a direction perpendicular to the direction of the propagation of the waves.
For longitudinal waves, the particles of the medium move in a direction parallel to the direction of the propagation of the waves.

Analysing Sound Waves

November 27, 2020November 27, 2020 by Veerendra

Analysing Sound Waves

Sounds are mechanical waves. They are caused by vibrating objects. The string of a guitar, the skin of a drum and a tuning fork, all of these vibrate to produce sound.
The vibrating cone of a loudspeaker in Figure produces sound. Its vibrating diaphragm is continually compressing and stretching the air next to it. This makes a series of compressions and rarefactions which travel through the air away from the loudspeaker.
A compression is a region of increased pressure and a rarefaction is a region of decreased pressure. The resulting succession of compressions and rarefactions constitutes the sound waves.
A sound wave is longitudinal in nature because the air molecules vibrate in the direction which is parallel to its direction of propagation.
A sound wave needs a medium for its propagation because its propagation is essentially due to the vibration of the molecules of its medium.
Compressions and rarefactions need a material which can be compressed and stretched. This explains why we do not hear any sound in space which mainly consists of a vacuum.

People also ask

Amplitude and Frequency of Sound Waves

The amplitude of sound waves is related to its loudness. The louder the sound, the bigger is its amplitude.
The frequency of sound waves is related to its pitch. The higher the pitch of the sound, the higher is its frequency.
Figure summarises the relationship between, amplitude and loudness; frequency and pitch of a sound.

Application of Sound Waves in Daily Life

Sound can be generated in a wide range of frequencies. Sound waves generated between 20 Hz and 20 kHz can be heard by normal human ears and are known as audio waves. Those below 20 Hz are called infrasonic and those above 20 kHz are known as ultrasonic.
A bat can navigate in complete darkness by emitting very high-pitched sound waves in the ultrasonic range.
(a) When these waves hit an object, they are reflected back and received by the bat.
(b) The time between the emission of the sound waves and the reception of the reflected waves enables the bat to estimate the position of the object accurately.
Dolphins use ultrasonic frequencies of about 150 kHz for communication and navigation.
Figure shows the process of detecting flaws inside a piece of metal using the echo sounding method.
(a) An ultrasonic transmitter sends out pulses of ultrasound in the metal.
(b) A receiver picks up the echoes from different parts of the metal and sends the information to a C.R.O.
(c) The C.R.O. displays the information on its screen. Pulse P is the transmitted pulse, pulse Q has been reflected by the flaw and pulse R is the echo from the end of the metal.
An ultrasonic ruler uses ultrasonic echoes to measure distance. Figure shows an ultrasonic ruler being used to determine the depth of the sea.
(a) Pulses of ultrasounds are directed from the ship to the seabed and a receiver attached to the ship detects the reflected pulses.
(b) The time taken by a pulse to travel to the seabed and return to the ruler enables the depth of the sea to be determined. The ruler can be calibrated to give the value of the depth directly.
Opticians and goldsmiths use ultrasound to clean spectacles, jewellery and ornaments. The water used for the cleaning purpose is vibrated by ultrasound. The vibrations shake off dirt attached to these objects.
Dentists use ultrasonic waves to vibrate and shake dirt and plaque off patients’ teeth.
Animals like elephants and rhinoceroses call to one another using infrasonic waves.

Amplitude and Frequency of Sound Waves Experiment

Aim: To study the effect of amplitude on the loudness and frequency on the pitch of sound.
Apparatus: Cathode ray oscilloscope (C.R.O.), audio signal generator, loudspeaker
Method:

Amplitude and Frequency of Sound Waves Experiment

The apparatus is arranged as shown in Figure.
The audio signal generator and C.R.O. are adjusted so that a sound is produced by the loudspeaker and a sine wave is observed on the screen of the C.R.O.
By fixing the frequency, the volume*of the audio signal generator is increased gradually. The observation is recorded.
By fixing the volume, the frequency of the audio signal generator is increased gradually. The observation is recorded.

Observation:

Adjustment done on the audio signal generator		Change in the sine wave on the screen of the C.R.O.		Change in the sound produced by the loudspeaker
Volume	Frequency	Amplitude	Frequency	Change in the sound produced by the loudspeaker
increased	Fixed	Increased	Unchanged	Louder
Fixed	Increased	Unchanged	Increased	FHigher pitch

Conclusion:
Based on Table, it can be concluded that
(a) the bigger the amplitude of the sound, the louder is the sound.
(b) the higher the frequency of the sound, the higher is the pitch of the sound.

What Is A Sonic Boom And How Is It Produced

September 7, 2016September 6, 2016 by Veerendra

What Is Sonic Boom

When a body moves with a speed which is greater than the speed of sound in air, it is said to be travelling at supersonic speed jet fighters, bullets, etc, often travel at supersonic speed, and when they do so, they produce a sharp, loud sound called a sonic boom.

The source moves at a speed greater than that of sound, sound waves travelling at the speed of sound, are left behind. The high-pressure layers due to sound waves originating at different points bunch together as shown in figure.

sonic-boom

Actually, these layers fall on the surface of an imaginary cone of which OA, OB is a part. The total pressure on the surface of this cone is very high. The source is at the apex of this cone. As the source moves ahead, it drags the cone together with it. when the surface of the cone reaches a person, the ears experience a sudden increase in pressure. After the surface crosses him, the pressure is suddenly reduced. This causes the person to hear a sharp, loud sound-the sonic boom.

A region consisting of a very-high-pressure layer followed by a lower-pressure layer travels through the space together with the cone. This is called a shock wave. This shock wave gives rise to the sonic boom when it reaches a person.

The shock waves produced by supersonic aircraft have enough energy to shatter glass and even damage weak structure.

What Is Ultrasound And Its Applications

March 30, 2017September 6, 2016 by Veerendra

What Is Ultrasound

The sound waves having frequency higher than 20,000 Hz is called ultrasonic waves or ultrasound. Human beings cannot hear ultrasound. Dogs, bats and dolphins can hear ultrasound.
For example bats and dolphins can hear sound waves having frequencies of about 150,000 Hz. Bats and dolphins detect the presence of any obstacle by hearing the echo of the sound produced by them.
Ultrasound finds many technological applications.

Audible Wave: The human ear is sensitive to sound waves of frequency between 20 Hz to 20 kHz. This range is known as audible range and these waves are known as audible waves.
Example: Waves produced by vibrating sitar, guitar, organ pipes, flutes, shehnai etc.

Ultrasonic waves: A longitudinal wave whose frequency is above the upper limit of audible range i.e. 20 kHz, is called ultrasonic wave. It is generated by very small sources.
Example: Quartz crystal

Infrasonic wave: A longitudinal elastic wave whose frequency is below the audible range i.e. 20 Hz, is called an infrasonic wave. It is generally generated by a large source.
Example: Earthquake.

Characteristics of Ultra Sound

Ultrasound (or ultrasonic waves) are found very useful due to the following reasons:

Ultrasound (or ultrasonic) waves are high frequency sound waves. So these waves have short wavelength. These short wavelength sound waves can be reflected back from the smaller objects. Thus, ultrasound can detect smaller objects (< 1 cm size). The sound waves in the audible range cannot detect or ‘see’ objects smaller than having size ranging from a few tens of centimeters to a few metres.
Ultrasound beam is more directional and can be aimed towards any target just like a torch. These waves remain undeviated over long distances.

Applications of Ultrasound

Some important applications of ultrasound are described below :

In ultrasonic spectacles for blind people: Such a spectacle is fitted with a transmitter and a receiver. The receiver produces a high or low sound in the person’s ear depending upon whether the object causing the echo is near or far.
For medical use: Ultrasound is used to detect any infirmity / deformity in the unborn baby (X-rays cannot be used for this purpose because X-rays may harm the unborn baby). In this method, an ultrasonic transmitter / receiver is moved across the mother’s stomach. Different tissues (skin, muscles, bones) reflect the sound waves differently to produce many echoes. The machine uses these echoes to construct a picture on the screen. Any deformity / infirmity in the baby can be detected and proper treatment could be prescribed.
This technology has been misused for knowing the sex of the unborn baby. It has been noticed that many people force the would-be mother to have an abortion if the unborn baby is identified to be a female baby. This practice is unethical and a social crime. Our Government has banned such practices. We all should work together to eradicate this social menace.
In echocardiography: In this medical diagnostic technique, ultrasonic waves are used to construct the image of the heart.
For determining the depth of sea: Ships use ultrasound to determine the depth of the sea by echo-sounding method. A transmitter on the ship sends ultrasound towards the sea-bed and the receiver receives the echo. From the time gap between the two signals, the depth of the sea can be estimated. This is illustrated below.
For clearing hard to reach places: Ultrasonic waves are also used for clearing hard to reach places, such as spiral tube, odd shaped machine parts / components, electronic components etc. The object to be cleaned is kept in the ‘cleaning solution’ and the solution is subjected to the ultrasonic waves. The high frequency (ultrasonic) waves stir up the dust / dirt particles. These particles get detached and the object is thoroughly cleaned.
Bats fly in the darkness of night without colliding with other objects by the method of echolocation. Bats emit high frequency ultrasonic squeaks while flying and listen to the echoes produced by the reflection of their squeaks from the objects in their path. From the time taken by the echo to be heard, bats can judge the distance of the objects in their path and hence avoid it by changing the direction. Bats search their prey at night by the method of echolocation.