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## Introduction to sound and waves

### Sound :

Everywhere we can find sound, there can be various sources of it like birds, humans, machines, instruments, bells, vehicles, television, radios, etc.

It is basically a form of energy that produces a sensation of hearing in ears.

We are having different forms of energy like mechanical energy, heat energy, light energy, etc.

One more thing we have learned is about conservation of energy which states that “energy can neither be created nor destroyed” we can just change it in one form to another. So, this phenomenon is also applicable for sounds.

For example- when we clap, a sound is produced. It means we are utilizing our energy to produce sound and we are actually producing sound.

Sound travels in a wave form.

### Wave :

Wave is a kind of disturbance that moves through a medium when the particle of the medium set neighboring particles into motion.

waves are of two types :

1.  Electromagnetic waves :

·   X – rays

·   Lightwaves

·   Infrared waves

·   Ultraviolet

·   Microwave

2.  Mechanical waves :

·   Transverse waves – eg. Polarized waves etc.

·   Longitudinal waves – eg. Sound waves etc.

·   Surface waves – eg. Water ripples etc.

The particles of the medium do not move forward but the disturbance is carried forward that causes the propagation of sound in a medium.

Hence, sound can also be known as a wave.

Production of sound somehow turns the particles in the medium into motion. Thus, they are also known as mechanical waves.

### Mechanical waves :

A wave that is produced when the object of the medium oscillates or move, is known as mechanical waves. Thus, sound waves are basically mechanical waves.

It is divided into two types :

1.  Longitudinal waves :

In these type of waves, the movement of the particle are parallel to the motion of the energy.

Sound waves are longitudinal because the particle of the medium is parallel to the direction of the propagation of the sound waves.

Here, the particles in the medium move to and fro or back and forth.

Example – sound waves, pressure waves etc.

2.Transverse waves :

In this type of wave, the movement of the particle is at right angle or perpendicular to the motion of the energy.

Here, the particles do not oscillate along the line of wave propagation but oscillate up and down about the mean position as the wave travels.

Example – light waves, polarized waves etc.

### 1. Sound: Production and propagation

Jagriti 01 Jan 1970

### Production of Sound :

The basic way for the production of Sound is “vibration”. When an object vibrates it produces sound.

It can be produced by plucking, scratching, rubbing, blowing, flapping, or shaking different objects, as while doing each mentioned activities vibration is produced among the particle of that object.

“Vibration” is a kind of rapid to and fro motion of an object. For example – stretching of a rubber band, a vibration of string, or surface of any musical instrument.

### How does sound propagate :

Vibrating objects produce sound.

The matter or substance through which sound is transmitted from the point of generation to the listener (starting point to ending point) is known as a medium, which can be solid, liquid or gas.

The particles of the medium do not travel all the way from the vibrating object to the ear.

For instance – when we speak the particle in the air gets displaced due to the pressure caused by the production of sound, which again exerts pressure on other adjacent particles and this process continues till the intensity of vibration gets over or the sounds reach our ears.

### Sound needs a medium to travel :

Sound needs a material medium to propagate like air, water, steel, etc. The most common medium through which sound can travel is air. It cannot travel through a vacuum (no air) due to the unavailability of disturbances in the medium.

At the time of propagation of sound when a vibrating object moves forward, it creates Region of High Pressure which is known as compression (C).

With alternate regions of compression, there is also a region of low pressure, which is produced when the vibrating object moves backward and this region of low pressure is known as a rare fraction (R).

As the object moves backward and forward consecutively, a series of compression and rarefaction will be created in the air which will ultimately form sound waves that will produce sound.

Pressure is related to the number of particles of the medium in a given volume or its density.

If the medium is dense, the pressure exerted by the particles of the medium will be more and vice versa.

Thus, propagation of sound is all about change in pressure of the medium.

### 2. Sound waves : Different Characteristics - Frequency, Amplitude, Pitch, Timber

Jagriti 01 Jan 1970
Characteristics of a sound wave :

A sound wave can be described by its :

•  Frequency

•  Amplitude

•  Speed

1.  Compression (C) – These are the regions where particles are crowded together and are represented by the upper portion of the curve that is known as the peak.

•  The region of maximum compression is represented by its peak.

•  Therefore, compressions are regions where density, as well as pressure, is high.

2.  Rarefactions (R) - These are the regions where particles are spread apart and are represented by the lower portion of the wave curve that is known as the crest.

•  These regions always have lower pressure.

•  The trough of a wave is known as the valley and a peak is called the crest.

3.  Wavelength - It can be well described as the distance between two consecutive compression (C) of two consecutive rarefaction (R).

•  It is usually represented by the Greek letter lambda (λ).

•  Its SI unit is metre (m).

4.  Frequency (f) -

•  It can be well described as the number of oscillations per unit time.

•  It can also be described as the number of compressions + number of rarefaction (oscillation) per unit time.

•  A complete oscillation can be described as the change in density from the maximum value to the minimum value and again to the maximum value.

Oscillation = rarefaction + compression

The SI unit of frequency was named as hertz in honour of Henry Rudolf Hertz.

•  It is represented by (v).

•  Its SI unit is Hertz having symbol (Hz).

5.  Time period -

•  It can be described as the time taken by two consecutive compressions or rarefaction to cross a fixed point is known as the time period of the wave.

• In other words, we can say that the time taken for one complete oscillation (compression + rarefaction) in the density of the medium is called the time period of the sound wave.

•  Its SI unit is second (s).

•  It is represented by the symbol (T).

We can relate frequency with time period :
$$v = { 1 \over T }$$
Or,    $$T = { 1 \over v }$$

6.  Pitch:  When we hear two sounds at the same time, originating from different objects or instruments, traveling at same speed and through the same medium but we find both the sounds different. This is because of different characters of sounds which includes pitch.

•  The faster the vibration of the source, the higher is the frequency and the higher is the pitch or, it is directly proportional to the frequency

•  A man's voice is flat having low pitch while a woman’s voice is shrill having high pitch.

•   It depends upon the size of the object, the type of the object and sound frequency.

7.  Amplitude - It is described as the maximum displacement of the particle or the magnitude (value) of the maximum disturbance in the medium on either side of the mean value.

•  It is represented by (A).

•  Its SI unit is metre (m).

•  It usually depends upon the force with which an object is made to vibrate, light force produce softer sound and vice versa, that’s why loudness and softness of a sound is basically determined by it.

8.  Timber or quality – It is a characteristic that enables us to differentiate between two sounds even if they have the same pitch and loudness.

9.  Tone – A sound having a single frequency is known as tone.

10. Note –
•  A sound that has more than one frequency or we can say, a mixture of several frequencies is known as note.
•  They are pleasant to listen.

11. Music - A sound that is pleasant to listen to and has a rich quality.

12. Noise - It can be described as an unpleasant sound.

13. Intensity of sound -
•   It can be described as the amount of sound energy passing each second through a unit area or,
•  A distance by which compression or rarefaction of the wave travels per unit time.

15. Loudness - It can be best measured by our ears. We may hear two different sounds of different intensity and still can decide which is louder.

### 3. Speed of sound in different media

Jagriti 01 Jan 1970

As we know that, the sound of thunder is heard a little later than the flash of light is seen. Thus, it is true that the speed of sound is much less than the speed of light.

Speed of light = 3 × 10 8 m/s

Speed of sound = 344 m/s

The sound cannot travel at the same speed in different mediums.

The speed of the sound in a medium is affected by the following things :

1.  It depends upon the density of the medium. For instance - The speed of sound is maximum through solid.

2.  It depends upon the temperature of the medium. For instance - As the temperature increases, so does the speed of sound.

3.  It also depends on the humidity in the air. For instance – As humidity increases, so does the propagation of sound.

### Sonic Boom :

When an object travels in the air with speed more than that of the sound, it results in sound with high energy.
This energy is loud enough that can break glasses or damage the buildings. The sound produced is a similarity to the sound of an explosion or thunderclap.

These objects exert a large amount of pressure on the air which causes the production of the shock waves in the air. These waves produce extremely large and loud sound waves which are known as Sonic Booms.

A good reflector of sound = The material through which sound can bounce off is known as Good reflector of sound.

For example – metals and walls ( metals or liquid ).
A bad reflector of sound = The material through which sound cannot bounce back is known as a bad reflector of sound.

For example – clothes, cotton or vacuum, etc.

### Reflection of Sound :

Like lights, sound can also get reflected or bounces off like a rubber ball, at the surface of solid or liquid and follows the same law of reflection.

This law states that the incident sound wave, the reflected sound wave and the normal, all the three lies in the same plane.

It can also be defined as the direction in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence.

Angle of incidence = angle of reflection
i.e., i = r

### Echo :

When we hear the same sound of something again and again in any medium, it is known as Echo.

For example – If we shout or clap near a suitable reflecting object such a tall building or a mountain, we hear the same sound of clap again a little later.

The sensation of sound persists in our brain for about 0.1 seconds.

It is basically produced or formed due to the reflection of sound in any medium.

For hearing distance echoes, the minimum distance of the obstacle from the source of sound must be  17.2 m.

Successive of multiple reflections of a sound wave – The phenomenon of hearing echoes more than once.

For example – Roaring of thunder.

### 4. Sound: Reverberation, and Range of Hearing

Jagriti 01 Jan 1970

### REVERBERATION :

It is the persistence of a sound after a sound is produced.

A reverberation is created when a sound signal is reflected multiple of times until it reaches a sound wave that can not be heard by human ears.

It usually takes place in a big hall or auditorium.

Excessively reverberation is highly undesirable due to which the roofs and walls of the auditorium are generally covered with sound-absorbing material like compressed fireboards, rough plaster for draperies.

The material of the seats is also selected on the basis of their sound-absorbing property.

### Advantages of Multiple Reflection of Sound :

Horns, megaphones, loudhailers, musical instruments like trumpets, and Shehanais all are designed to send sound in a particular direction without spreading it in all directions.

It helps listeners and audience to listen to the speaker.

This all could become possible just because of Multiple Reflection of Sound.

Medical instrument “stethoscope” which is used for the listening sound produced within the body and specially used for heart and lungs, works on the same phenomenon that is multiple reflections of sound.

The ceiling of conference halls, cinema halls, concert halls are made curved so that sound after reflection can and even curved soundboard may be placed behind the stage so that sound after reflection can reach all corners of the hall and can spread evenly across the width of the hall.

### Range of Hearing :

The audible range of sound for human beings is between 20 Hz to 20000 Hz (one Hz = one cycle/s)

The children under the age of five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz)

As people grow older their ears become less sensitive to higher frequencies.

On the basis of the range of frequencies of a sound, it has been categorized as “infrasonic sound” or “infrasound” and “ultrasonic sound” or “ultrasound”.

infrasoundultrasound
It refers to sound with a frequency below 20 Hz that can't be heard by humans.It refers to the sound with a frequency higher than the upper limit (20 kHz) which is audible to humans.
Rhinoceros whales and elephants can communicate using infrasound range.Bats, dolphins, porpoises, and moths of certain families can produce this frequency.
It is observed that some animals get disturbed before the earthquake as they can hear low-frequency infrasound which possibly alert the animals.It is observed that certain animals can hear each other using high-frequency ultrasound which helps them to escape & capture.
·It can be used to monitor some natural calamities like earthquakes, volcanic eruptions before it occurs by infrasonic waves.·It can be used to detect cracks and flaws in metal blocks and also to clean parts located in hard-to-reach places.
It is also used to stabilize myopia is young kids.It is used to break small stones formed in the kidneys.
It is also used in charting rocks and petroleum formation below the earth.It is also used to get images of the internal organs of the human body.
It is also used in ballistocardiography and seismocardiography to study the mechanics of the heart.It is also used in “ultrasonography” to examine the fetus during pregnancy.

### 5. Applications of Ultrasound (ultrasonic sound waves)

Jagriti 01 Jan 1970

1.  The high-frequency waves are known as ultrasound.

2.  They are extensively used in industries and for medical purposes.

3.  They can travel long distance despite the obstacles presents within the path.

4.  It is also used to clean parts located in hard-to-reach places. For example- a spiral tube, electronic components, odd-shaped parts, etc.

It is done by placing objects to be clear in a cleaning solution and then passing ultrasonic waves through them.

The high frequency helps the particles of dust, grease, and dirt to detached which finally makes the object thoroughly cleaned.

5.  They are also used to detect flaws and cracks in metal blocks.

Big structures like buildings, machines, scientific equipment, and bridges are made up of metallic components. Some of them while they carry small holes that are invisible to us but they can easily reduce the strength of the structure.

Hence, these waves pass through the metal blocks and detectors are used to detect the transmitted waves if there will be any small defect then the ultrasound wave will reflect back, which will indicate the presence of the flaw or defect.

6.  “Echocardiography” can also be performed using this wave, as they are made to reflect from various parts of the ‘heart’ that can form the image of the heart.

7.  The instrument “ultrasound scanner” which uses ultrasonic waves can also get images of internal organs of the human body such as uterus, gallbladder, kidney, etc.

It can help doctors to detect abnormalities such as stones in the gallbladder and kidney or tumors in different organs.

It can be done by passing ultrasonic waves through the tissue of the body which gets reflected back.

These waves are then converted into electrical signals that are used to generate images of the organs which are then displayed on the monitor.

By the same process, “ultrasonography” is also done to examine the foetus during pregnancy to detect defect or growth abnormalities.

8.  Ultrasound waves are excessively used to break small stones formed in the kidney into fine grains which are later flushed out with urine.

### 6. SONAR : “Sound Navigation and Ranging”

Jagriti 01 Jan 1970

“Sonar” can be defined as “Sound Navigation and Ranging”.

This device is used to measure the distance, direction, and speed of an underwater object by using the same ultrasonic waves.

It consists of two major devices – a transmitter and a detector ( or receiver).

It is usually fixed or installed in a boat or ship for their safety purpose.

The transmitter is used to produce and transmit ultrasonic waves that travel through water and after striking any objects on the seabed it gets reflected back and is sensed by the detector.

The detector is used to convert ultrasonic waves into electrical signals which are then appropriately interpreted.

The distance of the object can be calculated by knowing the speed of the sound in water and the time interval between the transmission and reception of the ultrasound. This phenomenon is known as “Echo-Ranging”.

The formula to calculate the distance of the object is  2d = v × t.

Thus, this technique is used to determine the depth of the sea and to locate underwater hills, submarines icebergs, valleys, sunken ships, etc.

How Do Bats Search Their Prey?

### 7. Structure of Human Ear and Hearing Aid

Jagriti 01 Jan 1970

### Structure of Human Ear :

Humans are privileged as they are able to hear with the help of an extremely sensitive device known as the “Ear”.

We receive audible frequencies from our surrounding which is then converted into electrical signals that are passed through a special nerve called “Auditory Nerve” to our brain.

The brain interprets the received signals and responds accordingly.

### Auditory parts of the human ear are as follows :

The human ear comprises the outer ear, middle ear, and the inner ear.

1. Outer Ear :

Pinna – The outer part of the ear which collects sound from the environment of surroundings.

Auditory Canal – The sound that is collected from the surrounding are passed through the auditory canal.

Eardrum or Tympanic Membrane – This is a thin membrane that is located at the end of the auditory canal.

The eardrum when receives a compression moves inward because of increased pressure. Similarly, when it receives rarefaction it moves outward due to a decrease in pressure.

As a result, the eardrum starts to vibrate inwards and outwards on receiving a sound wave.

2. Middle Ear :

It consists of three bones (hammer, anvil, and stirrup). These bones amplify vibration several times and transmit the amplified pressure variations to the inner ear.

3.
Inner Ear :

The pressure variation received from the middle ear is turned into electrical signals by “Cochlea” which are then sent to the brain via the auditory nerve.

The brain interprets the received electrical signals into sound which we perceive.

### Hearing Aid :

Some of the people who are differently-abled can suffer from hearing loss which needs a proper appliance that can help them deal with this loss and for that “Hearing Aid” is needed.

A hearing aid is a battery-operated, an electronic device that receives sound from the atmosphere and converts it into electrical signals.

These electrical signals or energy is passed by an amplifier which amplifies it to a sound and then transfers it to a speaker.

The speaker then converts electrical signals into sound waves that are further being sent to the ears, due to which we can hear clearly.

## Sound: Production and propagation

The basic way for the production of Sound is “vibration”. When an object vibrates it produces sound.  The matter or substance through which sound is

4.08M Join the discussion.

## Sound waves : Different Characteristics - Frequency, Amplitude, Pitch, Timber

Compression (C) – These are the regions where particles are crowded together and are represented by the upper portion of the curve that is known a

4.08M Join the discussion.

## Speed of sound in different media

The speed of the sound in a medium is affected by the 1.  It depends upon the density of the medium. For instance - The speed of sound is maximum

4.08M Join the discussion.

## Sound: Reverberation, and Range of Hearing

Reverberation is the persistence of a sound after a sound is produced. A reverberation is created when a sound signal is reflected multiple times un

4.08M Join the discussion.

## How do bats search their prey?

Bats generate high-pitched ultrasonic waves which are then reflected from the obstacle or prey and return back to bat’s ear.

4.08M Join the discussion.

## Applications of Ultrasound (ultrasonic sound waves)

The high frequency waves are known as ultrasound. ultrasonography is also done to examine the foetus during pregnancy to detect defect or growth abn

4.08M Join the discussion.

## SONAR : “Sound Navigation and Ranging”

“Sonar” can be defined as “ Sound Navigation and Ranging”  This device is used to measure the distance, direction and speed of underwater objects by

4.08M Join the discussion.

## Structure of Human Ear and Hearing Aid

A hearing aid is a battery-operated, an electronic device that receives sound from the atmosphere and converts it into electrical signals. Humans

4.08M Join the discussion.

Que. How do bats search their prey?
Ans.

Bats generate high-pitched ultrasonic waves which are then reflected from the obstacle or prey and return back to bat’s ear.

This phenomenon help bats to search out prey and fly in dark night.

Porpoises also use the same technique for navigation and location of food in the dark.

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