Mind map :: Chapter 12: Sound

• Produced by: Vibrating objects (e.g., tuning fork, vocal cords).
• Medium required: Travels in solids, liquids, and gases but not in vacuum.
• Wave Type: Longitudinal waves (compression & rarefaction).
• Propagation Speed Order: Solids > Liquids > Gases.

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• Longitudinal Waves: Particles move parallel to wave direction.
• Crest & Trough: Only in transverse waves (not for sound).
• Key Terms:
• Frequency (ν): No. of vibrations/sec (Hz) → Determines pitch.
• Amplitude (A): Maximum displacement → Determines loudness.
• Wavelength (λ): Distance between two consecutive compressions/rarefactions.
• Time Period (T): Time for one complete wave cycle.
• Speed of Sound (v): $$v = \lambda \times \nu$$
• Loudness: Measured in decibels (dB).
• Pitch: High-frequency = high pitch (e.g., child’s voice), Low-frequency = low pitch (e.g., adult male voice).

• Depends on:
  • Density of medium (higher density → higher speed in solids).
  • Temperature: In gases, speed increases with temperature.
  • Humidity: More water vapor → speed increases.

Speed of sound (approx.):

• Air (at 25°C) ≈ 344 m/s
• Water ≈ 1500 m/s
• Iron ≈ 5000 m/s

• Laws of Reflection: Same as light reflection.
• Echo:
  • Reflection of sound from a large surface.
  • Minimum distance = 17.2 m (at room temperature).
  • Time gap ≥ 0.1 sec for separate perception.
• Reverberation:
  • Multiple reflections cause prolonged sound.
  • Controlled by: Soft materials (curtains, carpets, acoustic panels).
• Applications:
  • SONAR (Sound Navigation and Ranging): Used in submarines & ocean exploration.
  • Ultrasound Scanning: Used in medical imaging (e.g., fetal scans).
  • Bats & Dolphins: Echolocation to navigate & hunt.

• SONAR: Uses ultrasound to detect underwater objects.
• Ultrasound: Used in medical imaging, cleaning, and flaw detection.
• Musical Instruments: Different instruments create different wave patterns.
• Seismology: Earthquake waves analyzed using sound wave principles.

• Born: 22 February 1857, Hamburg, Germany
• Education: University of Berlin

Key Contributions:

1. Confirmed Maxwell's Electromagnetic Theory.
2. Laid the Foundation for radio, telephone, telegraph, and television.
3. Discovered the Photoelectric Effect (later explained by Einstein).
4. Unit of Frequency: Named Hertz (Hz) in his honor.

Legacy:

Hertz’s work revolutionized communication and physics, shaping modern technology.

1. Outer Ear (Pinna & Auditory Canal): Collects sound waves.
2. Middle Ear (Eardrum & Ossicles): Converts sound into mechanical vibrations.
3. Inner Ear (Cochlea & Auditory Nerve): Converts mechanical signals into electrical impulses for the brain.

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