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Inaudible sounds are sounds of frequency that are not audible to the human ear. While, audible sound frequencies are audible to the human ear. A sound is a sequence of disruption generated by the flow of energy as it perpetuates outward from the origin of the sound via a medium (air, liquid, or any other semi solid matter). This is caused by a vibration-producing object, such as a phone ringing or a user's vocal chords.
Read about: Sound Waves
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Key Terms: Sound Waves, Longitudinal Waves, Transverse Waves, Wavelength, Frequency
Audible Sound
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Waves between 20 Hz and 20 kHz are easily detectable by the human ear. As a result, audible sound is defined as sound waves having a frequency spanning from 20 Hz to 20 kHz. If the pressure differences in the air are within the threshold of hearing, the human ear is responsive to them. It can identify pressure differences of about a billionth of an atmosphere.
Our ears become injured as we age and are subjected to sound for longer periods of time, and the upper bound of detectable frequencies lowers. The highest range that an average middle-aged adult can plainly hear is 12-14 kilohertz.
Audible Sound
Also Read: Loudness of Sound
Inaudible Sound
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Human ear is incapable of detecting or perceiving sound frequencies of less than 20 waves per second, or 20 Hz. As a result, any sound wave that falls below this wavelength is inaudible to humans. The human ear cannot identify or perceive wavelengths beyond 20,000 vibrations per sec (20 kHz) in the upper range, and the volume of the sound wave would be determined by its loudness.
As a result, frequencies below 20 Hz and over 20 kHz fall into the inaudible frequency range. Infrasonic sounds are low-frequency vibrations that the human ear is unable to sense or detect. Ultrasonic sound refers to inaudible frequencies in the upper range.
Classification of Sound
Properties of Sound Waves
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Let’s discuss about characteristics of sound:
Wavelength
The wavelength is the shortest distance over which a sound wave can renew itself. It is, in other words, the length of a single full wave. A Greek letter is used to represent it (lambda). The total length of a compaction and a neighbouring rarefaction of a sound wave is known as its wavelength. Also, the wavelength is equal to the distance between the centres of 2 sequential compressions or rarefactions.
Read more: Frequency and Wavelength
Amplitude
When a wave travels through a substance, the medium's particles are momentarily displaced from their natural, undisturbed places. When a wave propagates through a system, the amplitude of the wave is the maximum movement of the particles from their initial undisturbed positions. The amplitude, in reality, is employed to indicate the wave's size. The metre (m) is the SI unit of amplitude estimation, however it is sometimes expressed in centimetres.
Amplitude
Speed of Sound
The velocity of sound is the rate or velocity at which sound waves transmit or move across a medium. The velocity of sound varies depending on the medium. Solids have the fastest sound because their atoms are strongly compressed, whilst gases have the slowest sound since their molecular compaction is the lowest.
In an ideal gas, the speed of sound is determined solely by its concentration and temperature. In common air, the velocity has a weak relationship with frequency and density, departing slightly from optimal behaviour.
Sound Waves
Time Period
The time it takes to create a single complete wave, loop, or cycle is referred to as the wave's time-period. One full oscillation of the vibrating body now produces one complete wave. As a result, the time involved in completing one vibration is referred to as time-period. The letter T stands for it. The second is the standard of time measurement (s). The time period of a waveform reduces as the frequency of the wave rises.
Frequency
The spectrum of a sound (or audio) is the rate at which it vibrates, which defines the resonant frequency. Sound is produced by vibrations that travel through a material such as air and are detected by the ear or other equipment. The frequency of wave oscillations that happen in one second is quantified in Hertz, which is the universal unit of measurement (Hz). In other words, 1 Hz equals 1 vibration every second.
The kilohertz (kHz) is a larger unit of frequency, with 1 kHz equaling 1000 Hz. The letter f stands for the rate of a wave.
Infra Sound and Ultrasound
Things to Remember
- Longitudinal waves are another name for sound waves. That is, particle vibrations propagate in a path that is roughly parallel to the transmission of energy waves. Vibrations and rarefactions are terms for high-pressure and low-pressure zones, accordingly.
- Substances' sound-absorbing properties change dramatically with frequency. Low-frequency noises (less than 500 Hz) are more difficult to manage, but high-frequency sounds (greater than 500 Hz) are simpler.
- Two or more advancing waves can flow through the medium at the same time without interfering with one another's motion. As a result, the vector sum of the separations obtained by different waves independently equals the resulting displacement of each particle of the medium at each time. The superposition principle is the name given to this concept.
- When two waves with same frequency move in a medium in the same direction at the same time, the ensuing intensity at any place in the medium differs from the product of two waves' levels due to their superposition. The intensity of the resulting wave is quite high at some spots and very low or non-existent at others. Interruption of waves is the name given to this occurrence.
- A wave can travel through a substance or across space. In either case, the results are used to compute the wave speed. Through addition, the media in which the wave promulgates determines the wave's speed.
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Sample Questions
Ques. What are longitudinal and transverse Sound waves? (3 Marks)
Ans. There are two types of waves:
Longitudinal Waves- A waveform in which the medium's molecules vibrate back and forth in the 'same direction' as the wave moves. Solids, liquids, and gases can all be used as mediums. Sound waves are hence longitudinal waves.
Transverse Waves- A waveform in which the medium's components vibrate up and down 'at right angles' to the wave's path of motion. These waves can only be created in solids and fluids, not in gases.
Ques. What are ultrasonic Sound waves? (2 Marks)
Ans. Ultrasonic sounds are vibrations with a huge or excessively high frequency that cannot be detected or identified by the human ear. Ultrasonic noises are those that have a frequency greater than 20,000 hertz. Humans are incapable of hearing or perceiving ultrasonic sounds. Humans are unable to make ultrasonic sound waves or to detect ultrasonic noises.
Ques. What are Infrasonic sound waves? (3 Marks)
Ans. Infrasonic sound, often known as low-frequency sound waves, characterizes waves having a frequency underneath the human ear's lower bound of audibility (generally it is 20 Hz). As the wavelength of sound lowers, hearing becomes less delicate, hence the sound pressure must be sufficiently strong for humans to sense or detect infrasound. Rhinos, hippos, elephants, octopuses, pigeons, and other creatures that can converse or chat with one other utilising infrasonic sound.
Ques. What affects the Speed of the sound? (3 Marks)
Ans. The speed of sound is influenced by two key factors:
- Density of the medium: Any channel is required for sound to travel through it, and the concentration of the medium is one of the parameters that determines its speed. When the material is denser, the molecules are closer together, causing sound water to move faster. As a result, the observed speed of sound grows as the density of the material increases.
- Another factor is the temp of the medium through which it spreads: Sound waves and the temperature of the chosen medium are directly related or reliant on one other. The speed of sound rises as the temperature rises.
Ques. What are the Applications of Ultrasonic & Infrasonic Sound waves (5 Marks)
Ans. Applications of Infrasonic Sound Waves:
- Elephants and giraffes use infrasonic sound waves to converse over longer distances with their herds.
- Microphones are commonly used by scientists to follow herds of animals, even if they are buried in dense surroundings.
- Volcanic eruptions can be detected using infrared waves.
- Infrared sound can be used by scientists to track meteors in the air.
Ultrasonic Sound Waves Have a Wide Range of Applications:
- The hard materials must be cut and matched.
- Welding and ultrasonic soldering.
- Flow devices are being measured.
- In medicine, there are numerous applications.
- Ultrasonic as a way of long-distance communication.
Ques. Are Sound waves capable of generating heat?(3 Marks)
Ans. Sound waves can, in fact, generate heat. In truth, sound waves almost always emit a small amount of heat as they move and almost always absorb heat as well. Both sound and heat are macro representations of atoms and particles in motion.
The orderly motion of atoms and particles in rapid waving sequences is known as sound. The chaotic, unpredictable flow of atoms and molecules is known as heat. To convert sound into heat, all you have to do is convert some of the organized motion of the atoms and particles into disorganized movement.
Ques. What are Electromagnetic Waves? (3 Marks)
Ans. Electromagnetic waves, or EM ripples, are waves that are formed when an electric current and a magnetic field vibrate together. EM waves, in other terms, are made up of oscillating magnetoelectric fields.
When an electric field collides with a magnetic field, electromagnetic waves are created. As a result, they're called 'electromagnetic' waves. An electromagnetic wave's magnetic fields are perpendicular to one other (at right angles).
Ques. How are Electromagnetic Waves used in real life? (5 Marks)
Ans. Artificially created electromagnetic radiation pervades everyday life: microwave ovens cook food, radar waves direct planes, tv sets acquire electromagnetic waves produced by transmitting stations, and heaters emit infrared waves that offer warmth.
Automated self-focusing lenses that digitally measure and adjust the correct position of the object to be photographed also emit and receive infrared waves. Ultraviolet light is a form of electromagnetic radiation that is potentially detrimental to human health. This is also true of X-rays, which are useful in medicine since they allow doctors to see into the body, but should be avoided as much as possible.
Read about: Echo and Reverberation
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