Chapter 12: Sound

 

 Sound Production and Transmission

1. What is Sound?

• Sound is a form of energy that produces a sensation of hearing in our ears.
• It is generated by vibrating objects which create waves in the medium around them.

2. Forms of Energy

• Mechanical Energy: Involved in the movement of objects (e.g., moving vehicles, machines).
• Light Energy: Energy that is visible and can be seen by the human eye.
• Sound Energy: Sound energy is produced by vibrations in an object.

3. Energy Conservation

• The Conservation of Energy principle states that energy cannot be created or destroyed. It can only be transformed from one form to another.
• For instance, when you clap your hands, chemical energy in your muscles is converted into sound energy.

4. How is Sound Produced?

• Vibrations: Sound is produced when an object vibrates, causing disturbances in the medium (air, water, or solids).
• These vibrations create sound waves that travel through the medium to reach our ears.
• Examples: Clapping hands, striking a bell, plucking a guitar string.

5. Energy Used to Produce Sound

• When you clap your hands, the mechanical energy from your muscles is converted into sound energy, causing air particles to vibrate.
• It’s not possible to produce sound without using energy because the vibrations required to produce sound must come from some energy source.

6. Sound Transmission

• Sound requires a medium (solid, liquid, or gas) to travel. It cannot travel through a vacuum.
• Mediums for sound transmission: Air, water, steel, and others.
• The speed of sound differs in each medium. It is fastest in solids and slowest in gases.

7. Reception of Sound

• Sound waves travel to our ears, causing the eardrum to vibrate. This vibration is transmitted to the brain, which interprets the signals as sound.

Key Points:

• Sound is a form of mechanical energy.
• Energy conservation law applies to sound production.
• Vibrations of objects are the source of sound.
• A medium is required for sound to travel.
• Sound is received by the ears and interpreted by the brain.

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Production of Sound

1. Introduction to Sound Production

Sound is produced when an object vibrates, creating disturbances in the surrounding medium (air, water, solid). These vibrations travel as sound waves and reach our ears.

2. Activity 12.1: Vibrating Tuning Fork

• Objective: To observe the production of sound through vibration.
• Materials: Tuning fork, rubber pad, table tennis ball, thread.
• Procedure:
  1. Strike the tuning fork on a rubber pad to make it vibrate.
  2. Bring the vibrating tuning fork near your ear. Observation: You hear a sound as the vibrations travel through the air.
  3. Touch the vibrating tuning fork with your finger. Observation: You feel the vibration.
  4. Suspend a table tennis ball using a thread and touch it with the vibrating tuning fork. Observation: The ball moves due to the vibrations.
• Conclusion: Sound is produced by the vibration of objects. The vibration is necessary for sound production, as we observe movement or feel the vibration itself.

3. Activity 12.2: Vibrating Tuning Fork and Water

• Objective: To explore how vibrations affect different mediums (water).
• Materials: Tuning fork, beaker, glass of water.
• Procedure:
  1. Fill a beaker or glass with water up to the brim.
  2. Gently touch the vibrating tuning fork’s prong to the water surface. Observation: Small waves form on the water's surface due to vibrations.
  3. Dip both prongs of the tuning fork in the water. Observation: Stronger waves are generated, showing that sound vibrations can affect water.
• Discussion: When the vibrating prongs touch the water, they transfer their energy to the water, creating waves. This shows that sound energy can propagate through different media.

4. Key Conclusion: Can Sound Be Produced Without Vibration?

• No, sound cannot be produced without a vibrating object. In all activities above, the sound was generated by vibrating objects, such as the tuning fork. Vibration is essential for sound production.

5. How is Sound Produced?

• Vibration: Sound is produced by the vibration of an object. These vibrations create sound waves that travel through the medium (air, water, solid) to our ears.
• Examples of Vibrating Objects:
  • Human Voice: The vocal cords vibrate to produce sound.
  • Bird Flapping Wings: The movement of the wings creates sound.
  • Bee Buzzing: The rapid movement of the bee’s wings generates buzzing sound.
  • Rubber Band: When plucked, a stretched rubber band vibrates to create sound.

6. Activity 12.3: Identifying Vibrating Parts of Musical Instruments

• Objective: To identify which part of different musical instruments vibrates to produce sound.
• Materials: List of musical instruments (e.g., guitar, flute, drum, violin).
• Procedure:
  1. List different musical instruments.
  2. Discuss with your friends which part of each instrument vibrates to produce sound.
• Examples:
  • Guitar: The strings vibrate when plucked.
  • Flute: Air vibrates inside the flute when blown.
  • Drum: The drumhead vibrates when struck.
  • Violin: The strings vibrate when bowed or plucked.
• Conclusion: In every musical instrument, sound is produced by the vibration of some part of the instrument.

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Summary

• Vibration is the key to sound production. Any object that vibrates can create sound.
• Sound can be produced in various ways, including plucking, scratching, rubbing, and blowing.
• Musical instruments produce sound through the vibration of their parts, such as strings, air columns, or drumheads.
• Activities like striking a tuning fork or plucking a rubber band help us observe and understand sound production.

Propagation of Sound

1. Medium for Sound Propagation

• Sound is produced by vibrating objects.
• The substance or matter through which sound travels is called a medium.
• The medium can be:
  • Solid (e.g., metal)
  • Liquid (e.g., water)
  • Gas (e.g., air)
• Sound moves through the medium from the point of generation (vibrating object) to the listener’s ear.

2. How Sound Propagates

• When an object vibrates, it sets the particles of the medium around it vibrating.
• The particles do not travel from the vibrating object to the ear. Instead:
  • A particle in contact with the vibrating object is displaced from its equilibrium position.
  • This particle then exerts a force on the adjacent particle, displacing it as well.
  • After displacing the adjacent particle, the first particle returns to its original position.
• This process continues, creating a chain reaction where the disturbance (vibration) travels through the medium, ultimately reaching the listener’s ear.

3. Understanding Sound as a Wave

• A wave is a disturbance that moves through a medium, transferring energy without moving the medium's particles forward.
• The particles set neighboring particles into motion, creating a disturbance that travels through the medium.
• Sound can be visualized as a mechanical wave, where the particles of the medium vibrate to propagate the sound.
• Mechanical Waves: Sound waves are a type of mechanical wave, as they require a medium (solid, liquid, or gas) to travel through.

4. Sound Waves in Air

• Air is the most common medium through which sound travels.
• When a vibrating object moves forward:
  • It pushes and compresses the air, creating a region of high pressure called compression (C).
  • This compression moves away from the vibrating object.
• When the vibrating object moves backward:
  • It creates a region of low pressure called rarefaction (R).
• Compression and rarefaction alternate in the air, creating a sound wave that propagates through the medium.

5. Compression and Rarefaction

• Compression: A region of high pressure where air particles are densely packed together.
• Rarefaction: A region of low pressure where air particles are spread apart.
• Pressure is related to the density of particles in the medium. More particles per unit volume result in higher pressure, and fewer particles result in lower pressure.
• Sound Propagation: Sound can be visualized as the propagation of density variations (compressions and rarefactions) or pressure variations in the medium.

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Summary

• Sound travels through a medium by setting particles into vibration. The disturbance created by the vibrations is what moves through the medium, not the particles themselves.
• Sound waves consist of alternating regions of compression (high pressure) and rarefaction (low pressure).
• These pressure variations move through the medium and propagate the sound. This behavior can be visualized as a mechanical wave.

 Sound and Its Need for a Medium

1. Sound as a Mechanical Wave

• Sound is a mechanical wave, which means it requires a medium to travel through (solid, liquid, or gas).
• It cannot travel through vacuum (empty space), as there are no particles to transmit the vibrations.

2. Experiment: Sound Cannot Travel in Vacuum

• Materials: Electric bell, airtight glass bell jar, vacuum pump.
• Procedure:
  1. Suspend an electric bell inside an airtight bell jar.
  2. Connect the bell jar to a vacuum pump.
  3. Press the switch to turn on the electric bell. Observation: You will hear the sound of the bell, as the air in the jar allows sound propagation.
  4. Start the vacuum pump to gradually remove the air from the jar. Observation: As air is pumped out, the sound becomes fainter, even though the bell continues to ring.
  5. When the air inside the bell jar is nearly gone, the sound becomes very feeble.
• Question: What happens if the air is removed completely? Will you still hear the sound?
  • Answer: When all the air is removed (creating a vacuum), no sound will be heard because sound cannot travel through a vacuum. The lack of air particles means there is no medium to carry the sound vibrations.

3. Conclusion

• Sound needs a medium to travel. It is unable to propagate in a vacuum, as demonstrated by the bell jar experiment.
• In the experiment, as the air was gradually removed, the sound became weaker because fewer air particles were available to carry the sound waves.
• Without air (or any medium), sound cannot be transmitted, illustrating that sound cannot travel through a vacuum.

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Summary

• Sound is a mechanical wave and requires a material medium (like air, water, steel, etc.) to propagate.
• It cannot travel through a vacuum because there are no particles to carry the sound waves.
• The bell jar experiment clearly demonstrates that as air is removed, the sound fades and eventually becomes inaudible when there is no medium.

 Sound Waves as Longitudinal Waves

1. Sound Waves are Longitudinal Waves

• Sound is a longitudinal wave. In longitudinal waves, the particles of the medium move parallel to the direction of wave propagation.
• This means that the particles of the medium oscillate back and forth about their resting position, rather than moving from one place to another.

2. Activity 12.4: Observing Longitudinal Waves in a Slinky

• Materials: Slinky.
• Procedure:
  1. Stretch the slinky by holding both ends (one end by you, the other by your friend).
  2. Give the slinky a sharp push towards your friend.
  3. Observe the movement of the slinky. When you push and pull alternately, you will notice the following:
     • A marked dot on the slinky will move back and forth in the direction of the disturbance.
     • The coils of the slinky compress (come closer together) in some regions and spread apart in others.
• Observation:
  • The regions where coils are closer together are called compressions.
  • The regions where coils are further apart are called rarefactions.
  • The movement of the slinky represents the propagation of sound as compressions and rarefactions in the air.

3. Sound Propagation as Longitudinal Waves

• Sound propagates through a medium (like air) as a series of compressions (high pressure) and rarefactions (low pressure).
• The particles in the medium oscillate back and forth around their equilibrium positions, transferring energy without moving the particles to new locations.

4. Longitudinal vs. Transverse Waves

• Longitudinal Waves:
  • Particles move parallel to the direction of wave propagation.
  • Example: Sound waves.
• Transverse Waves:
  • Particles move perpendicular to the direction of wave propagation.
  • Example: Water waves (when a pebble is dropped into a pond).
• Light Waves are also transverse, but unlike mechanical waves, they do not require a medium to propagate, as light is an electromagnetic wave.

5. Key Differences Between Longitudinal and Transverse Waves

• Longitudinal Wave:
  • Particles move parallel to the wave’s direction.
  • Sound waves are longitudinal.
• Transverse Wave:
  • Particles move perpendicular to the wave’s direction.
  • Water waves and light waves are transverse.

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Summary

• Sound waves are longitudinal waves, where the particles of the medium move back and forth along the same direction as the wave is propagating.
• The slinky experiment demonstrates this by showing how compressions and rarefactions travel along the slinky.
• Sound moves in a series of compressions and rarefactions, similar to how a slinky moves when pushed.
• Transverse waves (like light or water waves) are different because the particles oscillate perpendicular to the wave direction.

Characteristics of a Sound Wave

1. Key Characteristics of Sound Waves

Sound waves can be described by the following characteristics:

• Frequency: Number of oscillations (vibrations) per unit time.
• Amplitude: Maximum displacement from the mean position (related to loudness).
• Speed: Distance traveled by the wave per unit time.

2. Graphical Representation of Sound Wave (Fig. 12.8)

• Compressions (C): Regions where the particles are close together, resulting in high pressure and high density.
• Rarefactions (R): Regions where the particles are spread apart, resulting in low pressure and low density.
• Crest and Trough:
  • The peak of the wave represents compression (maximum pressure).
  • The valley represents rarefaction (minimum pressure).
• Wavelength (λ): The distance between two consecutive compressions (or rarefactions), typically measured in metres (m).

3. Frequency and Time Period

• Frequency (f): The number of complete oscillations or cycles (compressions or rarefactions) per unit time. It is represented by 𝞶 (Greek letter nu), and its unit is Hertz (Hz).
  • Example: In beating a drum, the frequency is how many times the drum is struck in one second.
• Time Period (T): The time taken for one complete cycle (from one compression to the next compression). Its unit is seconds (s).
• Relationship between Frequency and Time Period: $$f = \frac{1}{T}$$ This means the frequency is the reciprocal of the time period.

4. Pitch and Frequency

• Pitch: The perception of sound's frequency. Higher frequency vibrations correspond to a higher pitch, while lower frequency vibrations correspond to a lower pitch.
• High Pitch: More compressions and rarefactions pass a point per unit time, producing a high frequency sound.
• Low Pitch: Fewer compressions and rarefactions pass a point per unit time, producing a low frequency sound.

5. Amplitude

• Amplitude (A): The maximum displacement of particles from their equilibrium position. It represents the magnitude of the disturbance.
• Loudness: The perception of sound’s amplitude. Larger amplitudes produce louder sounds.
  • Example: A soft sound is created by a small amplitude (small force applied), while a loud sound is created by a large amplitude (strong force applied).
• Effect of Distance on Amplitude: As sound moves away from the source, its amplitude and loudness decrease.

6. Speed of Sound

• The speed of sound is the distance a compression or rarefaction moves through the medium per unit time.
• Formula for Speed of Sound: $$v = \frac{\text{wavelength}}{\text{time}} = \frac{\lambda}{T}$$ where:
  • $v$ is the speed of sound,
  • $\lambda$ is the wavelength,
  • $T$ is the time period.
• Alternatively, using the relationship between frequency and time period: $$v = \lambda \times n$$ where $n$ is the frequency.

7. Quality of Sound (Timber)

• Quality (or Timber): The characteristic of sound that allows us to distinguish between different sounds of the same pitch and loudness.
  • Example: A violin and a flute may produce sounds with the same pitch and loudness, but their quality makes them sound different.
• Tone: A sound of a single frequency.
• Note: A sound produced by a combination of frequencies, which is usually pleasant to the ear.
• Noise: Unpleasant, irregular sounds that are not harmonious.

8. Derivation of Speed of Sound

The speed of sound can be expressed as:

$$v = \frac{\lambda}{T}$$

where:

• $v$ is the speed of sound,
• $\lambda$ is the wavelength,
• $T$ is the time period.

Since the frequency $n = \frac{1}{T}$, we can substitute this into the above equation:

$$v = \lambda \times n$$

Thus, the speed of sound is the product of the wavelength and frequency.

9. Conclusion

• Sound waves are characterized by frequency, amplitude, and speed.
• Frequency determines the pitch of the sound, while amplitude determines the loudness.
• The speed of sound depends on the medium through which it travels but is independent of the frequency for a given medium under the same conditions.

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Summary

• Frequency (f) determines pitch, and amplitude (A) determines loudness.
• Wavelength (λ) and speed (v) of sound are related by $v = \lambda \times f$.
• Pitch increases with higher frequency and decreases with lower frequency.
• The quality (timbre) allows us to distinguish sounds of the same pitch and loudness.

  Heinrich Rudolph Hertz

• • Birth: February 22, 1857, Hamburg, Germany.
  • Education: University of Berlin.
  • Scientific Contributions:
    • Confirmed James Clerk Maxwell’s electromagnetic theory through experiments.
    • Pioneered work that led to the development of radio, telephone, telegraph, and television.
    • Discovered the photoelectric effect, which was later explained by Albert Einstein.
  • Honors: The SI unit of frequency is named hertz (Hz) in his honor

Sound Intensity vs. Loudness

Sound Intensity

• Definition: The amount of sound energy passing through a unit area per second. It is a physical quantity that quantifies the energy transported by sound waves.
• Formula: $$\text{Intensity} (I) = \frac{\text{Energy passing through a unit area}}{\text{Time}}$$ The intensity of sound depends on the amplitude of the sound wave and the medium through which the sound travels. Intensity is typically measured in watts per square meter (W/m²).

Loudness

• Definition: Loudness is the subjective perception of the intensity of sound as detected by the human ear. It refers to how the brain interprets the sound based on intensity, frequency, and the sensitivity of the ear to different frequencies.
• Loudness is not solely determined by the sound's intensity. Two sounds of equal intensity may be perceived differently due to various factors, including:
  • Frequency Response: The ear is more sensitive to certain frequencies and less sensitive to others. For example, sounds in the mid-range frequencies (e.g., speech) are perceived as louder than those at very low or high frequencies, even if the intensity is the same.
  • Duration: A sound of longer duration may be perceived as louder compared to a short sound of equal intensity.
  • Perceptual Factors: The way the brain processes sound information may affect how we perceive loudness.

Difference Between Intensity and Loudness

• Intensity is a measurable physical property of sound, typically measured in decibels (dB).
• Loudness, on the other hand, is a subjective experience and depends on how the human ear perceives the sound.

Relationship between Intensity and Loudness

• Although intensity and loudness are related, they are not the same:
  • Intensity increases proportionally with the square of the amplitude of the sound wave.
  • Loudness increases with intensity, but the relationship is non-linear. A small increase in intensity can lead to a noticeable increase in loudness, but the relationship is not always one-to-one. As the intensity increases, the increase in perceived loudness diminishes after a certain point.

Conclusion

• Intensity is an objective measure of sound energy passing through a unit area per unit time.
• Loudness is a subjective experience of sound based on intensity and the ear's sensitivity to the sound's frequency and characteristics.

Speed of Sound in Different Media

The speed at which sound travels depends on the medium through which it propagates. The speed of sound varies based on several factors such as:

1. Type of Medium: Sound travels at different speeds in solids, liquids, and gases due to differences in the properties of these media.

   • Solids: Sound travels fastest in solids because the particles are more closely packed, which allows for quicker transmission of vibrations.
   • Liquids: Sound travels slower than in solids, but faster than in gases.
   • Gases: Sound travels slowest in gases because the particles are more spread out and it takes longer for vibrations to transfer from one particle to another.

2. Temperature of the Medium: The speed of sound increases with an increase in temperature. For example, in air, the speed of sound increases as the temperature rises.

3. Density of the Medium: In general, denser media (like solids) transmit sound faster because the molecules are closer together, allowing quicker propagation of vibrations.

Speed of Sound in Various Media at 25 ºC

State	Substance	Speed of Sound (m/s)
Solids	Aluminium	6420
	Nickel	6040
	Steel	5960
	Iron	5950
	Brass	4700
	Glass (Flint)	3980
Liquids	Water (Sea)	1531
	Water (Distilled)	1498
	Ethanol	1207
	Methanol	1103
Gases	Hydrogen	1284
	Helium	965
	Air	346
	Oxygen	316
	Sulphur Dioxide	213

Key Points:

• The speed of sound is fastest in solids (like aluminium) and slowest in gases (like sulphur dioxide).
• The temperature of the medium influences the speed: higher temperatures result in a faster speed of sound.
• In gases, lighter molecules (like hydrogen and helium) allow sound to travel faster compared to heavier gases like oxygen.

Sonic Boom

• Definition: A sonic boom is a loud, sharp sound produced when an object moves at a speed greater than the speed of sound (supersonic speed).

• Cause: When an object, such as a bullet or a jet aircraft, exceeds the speed of sound, it creates shock waves in the air. These shock waves carry a large amount of energy.

• Effect: The air pressure variations from these shock waves produce the sonic boom sound, which is very loud and sharp.

• Damage: Sonic booms have enough energy to break windows and even cause damage to buildings.

• Example: Supersonic aircraft like jet planes produce sonic booms as they fly faster than sound.

Reflection of Sound

• Definition: Reflection of sound occurs when sound waves bounce off a surface, such as a solid or liquid, similar to how light reflects off surfaces. The reflected sound follows the same laws of reflection as light.

• Laws of Reflection:

  1. The angle of incidence (the angle at which sound hits the surface) is equal to the angle of reflection (the angle at which sound bounces off).
  2. The incident sound wave, the reflected sound wave, and the normal (line perpendicular to the surface) all lie in the same plane.

• Conditions for Reflection: For effective reflection, the obstacle must be large enough to reflect sound waves, and the surface may be either polished or rough.

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Activity 12.5: Reflection of Sound Using Pipes

Objective: To observe the reflection of sound and verify the relationship between the angles of incidence and reflection.

1. Materials Needed:

   • Two identical pipes (made using chart paper, with sufficient length)
   • A clock or mobile phone set to vibrating mode
   • A table and wall

2. Procedure:

   • Place the pipes near a wall.
   • Place the clock or vibrating phone near one open end of the pipe.
   • Try to hear the sound through the other pipe.
   • Adjust the position of the pipes to best hear the sound.
   • Measure the angles of incidence and reflection and observe the relationship between them.

3. Variation: Lift one pipe vertically to a small height and observe any changes in the sound reflection.

This experiment helps to demonstrate how sound follows the laws of reflection, and how sound waves travel and reflect off surfaces.

Echo

• Definition: An echo is the reflection of sound that we hear after a delay. It occurs when sound waves are reflected by a large surface, such as a mountain, building, or any other obstacle.

• Conditions for Hearing an Echo:

  • The time interval between the original sound and the reflected sound must be at least 0.1 seconds.
  • If the time gap is less than 0.1 seconds, the sound waves will merge, and we will not hear a distinct echo.

• Calculation for Distance:

  • Speed of sound in air at 22°C is approximately 344 m/s.
  • For an echo to be heard distinctly, the total distance traveled by sound (from the source to the reflecting surface and back) must be at least 34.4 meters.
  • Therefore, the minimum distance between the sound source and the reflecting object should be 17.2 meters (half the total distance).

• Effect of Temperature:

  • The speed of sound depends on the temperature of the air, so the distance required for hearing an echo will change with varying temperatures.

• Multiple Echoes:

  • Echoes can be heard more than once due to successive reflections from multiple surfaces. For example, the rolling of thunder occurs as sound reflects off various surfaces, like clouds and the land.

This explains the phenomenon of echoes and how they depend on the speed of sound and the distance to reflecting surfaces.

Reverberation

• Definition: Reverberation is the persistence of sound in a large space, caused by repeated reflections from the walls, ceiling, and other surfaces. The sound continues to bounce around the space until it gradually diminishes to a point where it is no longer audible.

• Cause: It occurs when sound waves repeatedly reflect off surfaces in a large hall or auditorium. This causes the sound to persist longer than desired.

• Effect in Large Spaces:

  • In auditoriums, concert halls, or big halls, excessive reverberation can make it difficult to hear clearly, as sounds may overlap or create echoes that interfere with one another.

• Solution to Control Reverberation:

  • To reduce reverberation in such spaces, sound-absorbent materials are used on the walls, roof, and seating. These materials include:
    • Compressed fibreboard
    • Rough plaster
    • Draperies
  • The seat materials in these spaces are also chosen for their ability to absorb sound and reduce the persistence of unwanted noise.

This process helps to ensure clear acoustics in performance spaces, preventing distortion or confusion caused by reverberation.

Uses of Multiple Reflection of Sound

1. Megaphones, Loudhailers, Horns, and Musical Instruments:

   • These devices are designed to direct sound waves in a specific direction without allowing them to spread in all directions.
   • A common design feature includes a tube followed by a conical opening, which helps reflect sound successively and guides most of the sound waves forward toward the audience.
   • Examples: Megaphones, Horns, Trumpets, Shehnais.

2. Stethoscope:

   • A medical instrument used to listen to sounds within the body, such as heartbeats or lung sounds.
   • The sound produced by the patient’s body undergoes multiple reflections within the stethoscope, directing the sound toward the doctor’s ears.
   • This helps the doctor hear internal body sounds clearly.

3. Acoustic Design of Concert and Cinema Halls:

   • Ceilings in concert halls, conference halls, and cinema halls are often curved to ensure that sound, after reflection, reaches all corners of the hall evenly.
   • A curved soundboard may be placed behind the stage, ensuring that sound reflects off the soundboard and spreads evenly across the width of the hall.
   • This is crucial for ensuring clear sound distribution in large spaces.

Range of Hearing

1. Audible Range for Humans:

   • The human ear can hear sounds with frequencies ranging from 20 Hz to 20,000 Hz (20 kHz).
   • As people age, their sensitivity to higher frequencies decreases.

2. Infrasonic Sound (Infrasound):

   • Frequencies below 20 Hz are called infrasonic sounds.
   • Humans cannot hear these, but some animals, like rhinoceroses, whales, and elephants, use infrasound for communication.
   • Some animals, like dogs, can hear up to 25 kHz and can detect infrasound.
   • Earthquakes produce low-frequency infrasound before the main shock, which may be detected by animals.

3. Ultrasonic Sound (Ultrasound):

   • Frequencies above 20 kHz are called ultrasonic sounds.
   • Animals like dolphins, bats, and porpoises produce and use ultrasound.
   • Some moths and rats are sensitive to ultrasonic frequencies for detecting predators or communication.

4. Hearing Aids:

   • Hearing aids are used by individuals with hearing loss.
   • A hearing aid consists of a microphone that picks up sound, converts it into electrical signals, and then amplifies the signals with an amplifier.
   • The amplified signals are converted back into sound by the speaker and transmitted to the ear for clearer hearing.

Applications of Ultrasound

1. Cleaning:

   • Ultrasound is used to clean hard-to-reach parts, such as spiral tubes, electronic components, and odd-shaped parts.
   • Objects are placed in a cleaning solution, and ultrasonic waves are used to detach particles of dust, grease, and dirt, thoroughly cleaning the objects.

2. Detection of Cracks and Flaws:

   • Ultrasound is employed to detect cracks and flaws in metal blocks used in structures like buildings, bridges, and machines.
   • The ultrasound waves pass through the metal, and any flaw reflects the waves back, indicating the defect's presence.

3. Echocardiography:

   • Ultrasound waves are reflected from different parts of the heart, forming an image. This technique is used to examine and diagnose heart conditions.

4. Ultrasonography (Ultrasound Scanner):

   • An ultrasound scanner uses ultrasonic waves to create images of internal organs like the liver, kidney, and gall bladder.
   • It helps detect abnormalities, such as stones or tumours, and is also used to monitor foetal health during pregnancy.

5. Breaking Kidney Stones:

   • Ultrasound is used to break small kidney stones into fine grains, which are then flushed out with urine.

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SONAR (Sound Navigation and Ranging)

1. SONAR is a system that uses ultrasonic waves for measuring distance, direction, and speed of underwater objects.

   • It consists of a transmitter and a detector installed in a boat or ship.
   • The transmitter sends out ultrasonic waves, which reflect off objects (like the seabed) and are detected by the detector.
   • The time taken for the waves to travel to the object and back is used to calculate the distance: $$2d = v \times t$$ where v is the speed of sound in water, and t is the time interval between transmission and reception.

2. Applications of SONAR:

• Depth measurement of the sea.
• Locating underwater hills, valleys, icebergs, submarines, and sunken ships.

Use of Ultrasound in Bats and Porpoises

1. Bats:

   • Bats emit high-pitched ultrasonic squeaks to navigate and hunt for prey, especially in dark conditions.
   • The reflections of these ultrasonic waves bounce off obstacles or prey and return to the bat’s ears.
   • By analyzing the nature of the reflections, bats can determine the location, distance, and type of object or prey.

2. Porpoises:

   • Like bats, porpoises use ultrasound for navigation and to locate food in the dark.
   • They emit ultrasonic waves, and the echoes help them detect objects in their environment, aiding in hunting and avoiding obstacles.

This phenomenon is an example of echolocation, where animals use sound waves to "see" their surroundings in complete darkness.

Structure of Human Ear and Hearing Process

1. Outer Ear (Pinna):

   • The pinna collects sound from the surroundings.
   • The collected sound travels through the auditory canal.

2. Eardrum (Tympanic Membrane):

   • At the end of the auditory canal is the eardrum.
   • The eardrum vibrates when sound waves (compression and rarefaction) reach it.
     • Compression increases pressure, forcing the eardrum inward.
     • Rarefaction decreases pressure, causing the eardrum to move outward.

3. Middle Ear:

   • Bones in the middle ear (hammer, anvil, stirrup) amplify the vibrations from the eardrum.
   • These amplified vibrations are transmitted to the inner ear.

4. Inner Ear (Cochlea):

   • The cochlea in the inner ear converts pressure variations into electrical signals.

5. Auditory Nerve:

   • The electrical signals are sent to the brain via the auditory nerve.

6. Brain Interpretation:

   • The brain interprets the electrical signals as sound.