. Introduction to Sound

  • Sources of Sound: Humans, birds, machines, vehicles, televisions, radios, etc.
  • Definition: Sound is a form of energy that creates a sensation of hearing in our ears.
  • Conservation of Energy: Energy cannot be created or destroyed, only transformed from one form to another (e.g., clapping converts mechanical energy to sound energy).

2. Production of Sound

  • Key Concept: Sound is produced by vibrations. Vibrations are rapid to-and-fro motions of an object.
  • Examples:
    • Human voice: Vibrations in vocal cords.
    • Flapping wings of birds or buzzing of bees.
    • Plucking a stretched rubber band.

3. Propagation of Sound

  • Medium Requirement: Sound travels through solids, liquids, or gases, not in a vacuum (e.g., you cannot hear on the moon due to the absence of a medium).
  • How it Travels:
    • Vibrating objects cause particles of the medium to oscillate.
    • The disturbance moves forward, not the particles themselves.
  • Wave Nature:
    • Sound waves are mechanical waves because they need a medium.
    • These are also longitudinal waves, where particles move parallel to the direction of wave propagation.

4. Characteristics of Sound Waves

  • Compression and Rarefaction:
    • Compression (C): Region of high pressure/density.
    • Rarefaction (R): Region of low pressure/density.
    • Together, they form the sound wave.
  • Key Properties:
    1. Wavelength (λ): Distance between two consecutive compressions or rarefactions (Unit: meters).
    2. Frequency (ν): Number of oscillations per second (Unit: Hertz, Hz).
      • High frequency → High pitch (e.g., flute sound).
    3. Time Period (T): Time taken for one oscillation (T = 1/ν).
    4. Amplitude (A): Maximum disturbance from the mean position.
      • Larger amplitude → Louder sound.
    5. Speed (v): Distance a wave travels in unit time (v = λν).

5. Types of Waves

  • Longitudinal Waves: Particles oscillate parallel to wave propagation (e.g., sound waves).
  • Transverse Waves: Particles oscillate perpendicular to wave propagation (e.g., water waves).

6. Sound Quality

  • Loudness: Depends on amplitude (higher amplitude = louder sound).
  • Pitch: Related to frequency (higher frequency = higher pitch).
  • Timber (Quality): Helps distinguish sounds of the same pitch and loudness.
    • Tone: Sound of a single frequency.
    • Note: Mixture of multiple frequencies (pleasant).
    • Noise: Unpleasant sound.

7. Mathematical Relations

  • Speed of Sound:
    v=λν, (Wavelength × Frequency)

8. Practical Insights

  • Intensity: Energy passing through a unit area per second. Loudness is subjective and depends on how the ear perceives sound.
  • Medium Properties:
    • Denser mediums (e.g., solids) allow faster sound propagation compared to gases.

Reflection of Sound

  • Sound reflects off solid or liquid surfaces, much like a rubber ball bounces off a wall.
  • It follows the laws of reflection:
    • The angle of incidence = angle of reflection.
    • The incident sound, the reflected sound, and the normal lie in the same plane.
  • Large obstacles (smooth or rough) are necessary for sound reflection.

Extra Knowledge:

  • This principle is the basis of sonar systems used in submarines and ships to detect underwater objects.

Speed of Sound in Different Media

  • Sound travels faster in solids than in liquids, and fastest in gases. This is because the molecules are closer in solids, allowing energy transfer more efficiently.
  • The speed of sound increases with temperature.

Extra Knowledge:

  • Thunder is heard later than lightning because light travels faster (3×108 m/s3 \times 10^8 \, \text{m/s}3×108m/s) than sound.

Echo

  • Echo: Reflection of sound heard after a delay.
  • To hear a distinct echo, the sound must reflect back after at least 0.1 seconds.
    • Minimum distance of the obstacle: 17.2 m in air at 344 m/s.

Extra Knowledge:

  • Echoes are used in sonar and echolocation (e.g., by bats and dolphins) to detect objects or navigate.

Reverberation

  • Reverberation is the persistence of sound due to repeated reflections.
  • Excessive reverberation in halls is controlled by using sound-absorbing materials like:
    • Compressed fiberboards, curtains, or rough plaster.

Uses of Multiple Reflection of Sound

  1. Megaphones and Loudhailers: Direct sound towards the audience efficiently.
  2. Stethoscope: Multiple reflections amplify body sounds (heartbeat, lungs).
  3. Curved Ceilings/Soundboards: Ensure sound reaches all corners of halls.

Range of Hearing

  • Humans: Audible range 20 Hz to 20,000 Hz.
  • Below 20 Hz: Infrasound (e.g., elephants, earthquakes).
  • Above 20,000 : Ultrasound (e.g., bats, dolphins).

Extra Knowledge:

  • Animals detect infrasound before earthquakes, possibly explaining unusual behavior.

Applications of Ultrasound

  1. Medical:
    • Echocardiography: Imaging the heart.
    • Ultrasonography: Imaging internal organs and monitoring fetal growth during pregnancy.
    • Kidney Stone Treatment: Break stones into smaller particles.
  2. Industrial:
    • Detecting cracks in metal blocks.
    • Cleaning intricate components using ultrasonic vibrations.

Extra Knowledge:

  • Sonography is non-invasive and safer than X-rays for certain uses.

Key Learnings

  1. Sound travels as a longitudinal wave, carrying energy, not particles.
  2. Wavelength (λ): Distance between two compressions or rarefactions.
  3. Speed (v), frequency (ν), and wavelength are related: v=λν.
  4. Intensity of sound determines its loudness.
  5. The laws of reflection apply to both sound and light.

Extra Knowledge for Competitive Questions:

  • Applications of Echo:
    • Measuring distances (e.g., sonar in oceans).
    • Studying architectural acoustics.
  • Sound absorption coefficients of materials are critical in hall designs to avoid echoes and reverberation.

THESE ALL ARE THE NOTES OF CHAPTER 11 SCIENCE. AND AFTER SOME TIME YOU GET IMPORTANT QUESTIONS HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊