What is Sound? Its Transmission, Acquisition, Movement and Effect

What is sound?

Sound is a type of energy, the origin of which is produced by the vibration of some object, it can be understood with the help of an example, like when we hit a bell, we hear the sound and the bell is lightened. On touching it, there is a feeling of tingling in it. As soon as the vibration of the bell stops, the sound also stops. But it is not necessary that every vibration produces sound. The sound waves, whose frequency is between 20 Hz to 20,000 Hz, that humans can perceive only through their ears, are called sound waves. Sound waves are longitudinal mechanical waves. When a medium vibrates, sound is produced.

Transmission of sound:

In order for sound to travel from one place to another, it is necessary to have some substance, medium, gas, liquid or solid, sound cannot travel through vacuum, sound is produced in vacuum but it is not heard. Sound depends on the elasticity and density of the medium, which is not elastic, it cannot be transmitted over a long distance. In daily life, the sound generated from a sound source usually reaches our ear through air, but sound can also travel through liquid and solid.

This is the reason why the diver can hear the sound even when he is under water. Temperature also has an effect on the speed of sound. An increase of 1 degree Celsius in temperature results in an increase in the speed of sound by 60 cm/s. Similarly the sound of a train approaching from a long distance can be heard by putting one ear to the railway track. Sound travels in any medium as longitudinal waves.

Sound acquisition:

Normally we perceive sound through our ears. When the sound waves from a vibrating object hit the eardrum, the same type of vibrations occur in the screen. So this gives us the experience of sound.

Speed of sound:

Scientific experiments show that for the movement of sound, the same object can serve as a medium, which has elasticity and which extends uninterruptedly from the sound source to the ear. Objects which do not have these properties, such as wood sawdust, salt, etc., cannot pass through them. The speed of sound is different in different mediums. The speed of sound is greater in liquids than in gases and the highest in solids. When sound travels from one medium to another, the speed and wavelength of the sound change, while the frequency does not change. Thus, the speed of sound through a medium does not depend on the frequency of the sound.

The effect of various factors on the velocity of sound:

Velocity of sound in gases:- The formula for the velocity of sound in gases is- Where γ = isentropic expansion factor or adiabatic coefficient, R = universal gas constant T = temperature (in Kelvin) M = is the molecular mass of the gas.

Velocity of sound in solids:- where E is the Young's modulus of the solid and ρ is the density of the solid. From this formula the velocity of sound in steel can be calculated which is about 5148 m/s.

Velocity of sound in liquids:- The importance of the velocity of sound in water is because it is used to map the depth of the ocean floor. The velocity of sound in salt water is about 1500 m/s while in pure water it is 1435 m/s. The velocity of sound in water varies mainly with pressure, temperature and salinity etc. The velocity of sound in liquid is given by the following formula- where K' is the bulk modulus and ρ is the density of the fluid. Velocity of sound in different mediums : Solid > Fluid > Gas

Electromagnetic Radiation:

Electromagnetic waves are different from mechanical waves, which can also travel in vacuum, no physical medium is necessary for their propagation. They move at the speed of light, these waves are transverse light waves. Electromagnetic waves are produced by the free state oscillations of charged radicals such as electrons, protons, etc. Light, thermal radiation, X-rays, radio-waves etc. are their well-known forms. The general introduction of electromagnetic waves is as follows-

1. Gamma-rays: Gamma-rays are also called baccal rays after their discoverer. Their wavelength ranges from 10-¹⁴ meters to 10-¹⁰ meters. Due to their high frequency, they carry a lot of energy with them. Their penetrating power is so high that it is 30 cm. They pass through the thick iron sheet.
2. These rays are also called Roentz rays after their discoverer. They are produced by the collision of terrific electrons on a heavy target object. In medicine, they are used to diagnose broken bones and lung diseases.
3. Ultraviolet radiation: This radiation was detected by Ritter. Their wavelength ranges from 10–⁸ m to 4 × 10–⁷ m. They are detected by the photoelectric effect, fluorescent screen or photographic plate. They are used for irrigation, producing photoelectric effect, destroying harmful bacteria, etc.
4. Visible Light: The wavelength of visible light ranges from 4.0 x 10-⁷ m to 7.8 × 10-⁷ m. Happens till. Apart from the sun and stars, their sources are flames, electric-bulbs, arc lamps etc. It is through light that we see things.
5. Infrared radiation: These radiations were detected by Herschel. Their wavelength ranges from 7.8 × 10–⁷ m to 103 m. They are obtained from hot objects and the sun. The object on which it falls, its temperature increases.
6. Hertzian Waves: These were discovered by scientist Heinrich Hertz. In common language, they are also called wireless-waves or radio-waves. Their wavelength can range from 10³ meters to 104 meters. They originate from the flow of high frequency alternating current in an electrical conductor.

These waves are also called short radio waves. In these, the waves of wavelength 10 -3 meters to 10-2 meters are called micro waves. They are used in the transmission of television, telephone etc. Electromagnetic waves of wavelength up to 1 meter 104 meters are called wireless or long radio waves.

Frequency Range of sound:

1. Audible Waves: Those waves, whose frequency is 20 Hz and maximum frequency of 20,000 Hz and which we can hear, are called audible waves. Humans cannot hear waves of frequency less than 20 Hz because these waves do not sense the eardrum and the frequency of waves above 20,000 Hz is so high that the oscillation of the eardrum cannot be so high that it to receive these waves. Bats have a very high hearing range. They can generate and hear waves of 100,000 hertz. Dogs can easily hear waves up to 20,000 Hz.
2. Infrared Waves: Those mechanical waves, whose frequency is less than 20 Hz, are called infrared waves. These waves are generated inside the earth during earthquakes. The frequency of our heartbeat is similar to that of an inaudible wave. We cannot hear these waves.
3. Ultrasonic Waves: Those mechanical waves, whose frequency is more than 20000 Hz or 20 kHz, are called ultrasonic waves. These waves were first generated by Galton by a whistle. Human ears cannot hear these waves, but some animals, such as dogs, cats, dolphins, birds, etc., can hear them.

Signs of sound:

There are three main characteristics of sound – intensity, pitch and quality.

• Intensity: The intensity of sound depends on the amplitude of vibration of the vibrating object producing the sound. The greater the amplitude of the vibration, the greater the intensity of the sound. The intensity of sound is measured in decibels. A sound of 50 decibels is enough to wake a sleeping person. 90 decibels is the maximum limit for tolerating any noise. The larger the size of the vibrating object, the greater the amplitude of vibrations will be produced, due to which the intensity of the sound produced will be higher and the louder the sound will be heard.
• Tolerance: The characteristic of sound due to which we call sound as thick or thin is called pitch. The pitch of sound depends on its frequency. The pitch of the sound of males is lower than that of females. In the roar of a lion and the buzz of a mosquito, the buzz of a mosquito has a high pitch and that of a roar of a lion is low.
• Quality: It is the characteristic of sound by which the number of sounds of the same frequency or of the same intensity depends on their sum and their relative intensity. The quality of sound depends on the number of overtones present in it, their sum and their relative intensity. Due to the quality of sound, we recognize our various acquaintances by listening to their voices without seeing them.

Main features of sound:

• Sound is a mechanical wave and not an electromagnetic wave. (Light is an electromagnetic wave.
• On passing from one medium to another, there is reflection and refraction of sound.
• Microphone converts sound into electrical energy; Loudspeaker converts electrical energy into sound energy.
• A medium is needed for the propagation of sound. The propagation of sound is possible in solid, liquid, gas and plasma. Sound cannot propagate in vacuum.
• Echo - The reflected sound is called echo. To hear a clear echo, the reflecting surface should be at least 17 meters away from the listener, and the time should be 1 second.
• The speed of sound in air at normal temperature and pressure (NTP) is about 332 meters per second. Many aircraft that can travel faster than this are called supersonic aircraft.
• The principle of resonance is used to determine the depth of the ocean, radar and the position of submarines in the ocean, etc.
• The human ear can only hear sound waves ranging from about 20 Hz to 20,000 kHz. Many other animals can hear waves of much higher frequency than this.
• In liquids, gases and plasma, sound travels only as a longitudinal wave, while in solids it can also travel in the form of a transverse wave. The medium in which sound is propagated if its particles vibrate in the same direction as the speed of sound, then it is called a longitudinal wave; When the particles of the medium vibrate perpendicular to the direction of motion of sound, it is called a transverse wave.
• Refractive Resonance: When two big rocks or big buildings are located parallel and at a proper distance and a sound is produced between them, then that sound will be reflected again and again from both the rocks respectively. This type of reflected sound is called refracted resonance. Due to repeated reflection from the reflectors, all these echoes together produce the sound of thunder. This is also the reason for the thunder of lightning, because the clouds, mountains etc. act as reflective surfaces.

Noise pollution:

Noise pollution or excessive noise is called any kind of unusable sounds, which cause problems to humans and animals. The main reason for this is the noise generated during the traffic. Along with population and development, the number of traffic and vehicles also increases, due to which the noise pollution during traffic also starts increasing. There is also a risk of loss of hearing due to excessive noise. It is very rare that noise pollution causes any physical damage. This happens only when a person has to live for a long time in such a very strong level of noise which is much higher than the noise of normal life. The common man rarely has to stay in such noise for a long time that his hearing can be permanently damaged. But a frequency of about 1000 Hz can have a temporary effect on the body, if its intensity level is 100 decibels. An example of this is the temporary deafness of airborne soldiers.

Radio and television broadcasting: Radio waves sent by radio stations are reflected by the ionosphere, so they can be received anywhere on Earth. During the night, the layers of the ionosphere become stable, so radio transmission is better at night. Waves containing high frequency television signals cross the ionosphere and go out. Therefore, they are directly sent from one transmitting antenna to another receiving antenna. Therefore, the height of the transmitter antenna is kept as high as possible. Transmission is possible up to a distance of 80 km with a 500 meter high antenna. Nowadays television signals can also be carried to many places on the earth plane using geostationary satellites. 

Radar: Radar is an acronym for radio detection and ranging. Enemy ships and aircraft are detected by using micro waves in radar. The waves are transmitted by a revolving aerial and they are reflected from the target of the aircraft, ship etc. and returned to the radar. The distance of the vessel can be found by finding the time difference of the transmitted and received waves. The image of the area being scanned by the waves also comes on the radar screen.

Interference of sound: When two sound waves of equal frequency and amplitude reach a point simultaneously, the sound energy is redistributed at that point. This is called interference of sound. This interference is called accelerating, when both the waves reach a point in the same phase. In this case the resultant amplitude is equal to the sum of the different amplitudes of both the waves and the intensity of the sound is maximum and if both the waves meet in opposite phase then the interference is said to be destructive. In this direction the intensity of sound is minimum.

Diffraction of sound: When we are inside our room, we can easily hear the noise or conversation coming from outside. That is, we hear the sound produced without seeing the source. The reason for this is that when there is an obstacle in the path of sound, then these waves bend it and reach our ear. This is called diffraction of sound. For diffraction, it is necessary that the size of the barriers should be comparable to the wavelength of sound. Since the wavelength of sound is about one meter and the doors and windows of our house are of this category, due to which the diffraction of sound takes place easily and we can feel the sound coming from the source without seeing it.

Reflection of sound: Like light, sound also travels through one medium and returns to the first medium when it strikes the surface of another medium. This process is called reflection of sound. Reflection of sound also takes place according to the law of reflection of light, but due to the longer wavelength of sound, the reflection occurs from large sized surfaces. That's why the sound gets reflected from the walls, mountains and the surface of the earth. 

Refraction of sound: When sound waves travel from one medium to another, they get refracted, that is, they deviate from their path. The refraction of sound waves occurs due to the different layers of air having different temperatures. Because the speed of sound in hot air is higher than in cold air. That is why when sound waves are transmitted from hot air to cold air or from cold air to hot air, they deviate from their path.

Hertz: Heinrich Rudolf Hertz was born on February 22, 1857 in Hamburg, Germany, and was educated at the University of Berlin. He J.C. Maxwell's electromagnetic theory was confirmed by experiments. He also laid the foundation for future development of radio, telephone, telegraph and television. He also discovered the photoelectric effect, which was later explained by Albert Einstein. The SI unit of frequency is named in his honour,

Echo sounding: a sound wave emitted to measure the depth of an ocean or ocean, which strikes the ocean floor and returns. The depth is determined based on the time taken for the echo to return.

Sonar: Objects in water are detected by sonar. Ultrasonic waves are used in sonar Sonar was invented by Paullenguin. Sonar is a technology that uses sound transmission for navigation, underwater communication, and detection of objects under water or on the surface. The word 'Sonar' in English is basically a short form of Sound Navigation And Ranging.

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