Exercise Solutions (From Screenshot Page 109)

Q1: Fill in the blanks.

1. Sound is produced by vibrations.
2. Sound needs a medium to travel.
3. Sound cannot travel through a vacuum.
4. The speed of sound is fastest in solids.
5. The speed of sound is slowest in gases.
6. The maximum displacement of particles from their mean position is called amplitude.
7. The number of oscillations per second is called frequency.
8. The unit of frequency is Hertz (Hz).
9. The characteristic of sound that depends on amplitude is loudness.
10. The characteristic of sound that depends on frequency is pitch.
11. The human audible range is from 20 Hz to 20,000 Hz.
12. Sounds with frequencies below 20 Hz are called infrasonic sounds.
13. Sounds with frequencies above 20,000 Hz are called ultrasonic sounds.
14. The repetition of sound due to reflection is called an echo.
15. The persistence of sound in a large hall due to repeated reflections is called reverberation.
16. Excessive or unwanted sound is called noise pollution.
17. The unit of loudness is decibel (dB).
18. Bats use ultrasound for navigation.
19. SONAR stands for Sound Navigation And Ranging.

Q2: Match the pairs.

(Note: As an AI, I cannot create interactive matching. I will provide the correct pairs.)

• Vibration - Production of sound
• Amplitude - Loudness
• Frequency - Pitch
• 20 Hz - Lower limit of audible sound
• 20,000 Hz - Upper limit of audible sound
• Echo - Reflection of sound
• Reverberation - Persistence of sound
• Cochlea - Inner ear
• SONAR - Underwater navigation
• Sonography - Medical imaging

Q3: Give scientific reasons.

1. Sound cannot travel through a vacuum.
   Reason: Sound is a mechanical wave, which means it requires a material medium (like solids, liquids, or gases) for its propagation. Sound travels by causing the particles of the medium to vibrate and transmit energy. In a vacuum, there are no particles present, so there is no medium for the vibrations to travel through, and thus sound cannot propagate.
2. Steam causes more severe burns than boiling water at the same temperature.
   Reason: Steam at 100°C contains additional energy in the form of 'latent heat of vaporization' compared to boiling water at 100°C. When steam comes into contact with the skin, it condenses into water, releasing this large amount of latent heat (approximately 2260 kJ/kg or 540 cal/g). This extra heat energy, in addition to the sensible heat, causes more severe and deeper burns compared to boiling water, which only transfers its sensible heat.
3. Auditoriums have sound-absorbing materials on their walls.
   Reason: Auditoriums have sound-absorbing materials (like curtains, carpets, acoustic panels, foam) on their walls and ceilings to reduce excessive reverberation. Reverberation is the persistence of sound due to multiple reflections, which can make speeches or music unclear. By absorbing sound, these materials reduce the number of reflections, making the sound clearer and more distinct for the audience.
4. Bats use ultrasound for navigation.
   Reason: Bats use a process called echolocation, which relies on ultrasonic sound waves, for navigation and hunting in the dark. They emit high-frequency ultrasonic sounds that travel outwards. When these sound waves strike an object (like an insect or an obstacle), they reflect back as echoes. Bats can detect these echoes and, by analyzing the time taken for the echo to return and its characteristics, they can accurately determine the location, size, and movement of objects around them, allowing them to fly and hunt in complete darkness.

Q4: Answer the following questions.

1. Explain the production and propagation of sound.
   Answer: Production of Sound: Sound is produced by vibrations. When an object vibrates (moves rapidly back and forth), it disturbs the particles of the surrounding medium (like air, water, or solid). These disturbed particles then transfer their vibrations to adjacent particles, initiating a chain reaction. Propagation of Sound: Sound travels as a longitudinal wave through a material medium. The vibrations of the particles are parallel to the direction of wave propagation, creating regions of compression (high pressure) and rarefaction (low pressure) that travel through the medium. Sound cannot travel through a vacuum because there are no particles to vibrate and transmit the energy. The speed of sound is fastest in solids, slower in liquids, and slowest in gases.
2. Explain the characteristics of sound.
   Answer: Sound waves have several key characteristics:
   • Amplitude: The maximum displacement of particles from their mean position. It determines the loudness of the sound. Larger amplitude means louder sound.
   • Frequency: The number of vibrations or oscillations per second, measured in Hertz (Hz). It determines the pitch of the sound. Higher frequency means higher pitch (shriller sound).
   • Wavelength: The distance between two consecutive compressions or rarefactions.
   • Speed: The distance covered by the sound wave per unit time (v = f × λ).
   • Quality or Timbre: The characteristic that allows us to distinguish between two sounds of the same pitch and loudness produced by different sources (e.g., different musical instruments). It depends on the waveform of the sound.
3. Explain the reflection and absorption of sound.
   Answer: Reflection of Sound: Like light, sound waves can bounce off surfaces.
   • Echo: A distinct repetition of sound heard due to the reflection of sound from a distant hard surface (e.g., a wall, mountain). For a clear echo, there needs to be a sufficient distance between the source and the reflecting surface.
   • Reverberation: The persistence of sound in a large enclosed space (like a hall) due to multiple, continuous reflections from walls, ceiling, and floor. Excessive reverberation can make sound unclear and muddled.
   Absorption of Sound: When sound waves strike a surface, some of the sound energy is absorbed by the material, rather than being reflected. Soft, porous, and rough materials are good absorbers of sound. Sound absorption is used to reduce echoes and reverberation in auditoriums and recording studios by covering surfaces with materials like curtains, carpets, and acoustic panels.
4. Explain the structure and function of the human ear.
   Answer: The human ear is divided into three main parts:
   • Outer Ear: Consists of the pinna (visible part) and the ear canal. The pinna collects sound waves from the surroundings and directs them down the ear canal.
   • Middle Ear: Separated from the outer ear by the eardrum (tympanic membrane). It contains three tiny bones called ossicles (malleus, incus, and stapes). Sound waves cause the eardrum to vibrate, and these vibrations are amplified and transmitted by the ossicles to the inner ear.
   • Inner Ear: Contains the cochlea, a snail-shaped, fluid-filled structure. The amplified vibrations from the middle ear are converted into electrical signals by specialized hair cells within the cochlea. These electrical signals are then sent to the brain via the auditory nerve, where they are interpreted as sound.
   The ear's overall function is to convert sound vibrations into electrical signals that the brain can understand, enabling hearing.

Q5: Differentiate between.

1. Loudness and Pitch
   

   Feature	Loudness	Pitch
   Dependent On	Amplitude of the sound wave	Frequency of the sound wave
   Effect	Determines how strong or faint a sound is (e.g., soft vs. loud)	Determines how shrill or flat a sound is (e.g., child's voice vs. man's voice)
   Unit	Decibel (dB)	Hertz (Hz)

2. Echo and Reverberation
   

   Feature	Echo	Reverberation
   Nature	Distinct repetition of sound	Persistence of sound due to multiple reflections
   Distance Required	Requires a sufficient distance to reflecting surface (e.g., >17.2m)	Occurs in enclosed spaces, even with short distances
   Clarity	Clear, distinct repeated sound	Can make sound unclear or muddled
   Cause	Reflection from a single, distant surface	Multiple, closely spaced reflections from various surfaces