Chapter 11: Sound

11.1 Production of Sound

Sound is a form of energy produced by vibrations. A vibrating object sets the particles of the surrounding medium into motion, transmitting the sound through it.

Key Mechanism Sound waves are Mechanical Waves because they require a material medium (solid, liquid, or gas) for propagation. They cannot travel through a vacuum.

11.2 Propagation of Sound

Sound travels as Longitudinal Waves, where particles move back and forth parallel to the direction of wave propagation. This creates regions of high pressure (Compressions) and low pressure (Rarefactions).

11.2.2 Characteristics of a Sound Wave

Frequency (ν)

Number of oscillations per unit time. Measured in Hertz (Hz). Determines Pitch.

Amplitude (A)

Maximum disturbance from the mean position. Determines Loudness.

Speed (v) = λ × ν

λ: Wavelength | ν: Frequency

11.3 Reflection of Sound

Sound reflects off surfaces just like light. Key phenomena:

  • Echo: Repetition of sound caused by reflection. Persists for 0.1s in the brain. Min distance for echo is ~17.2m.
  • Reverberation: Persistence of sound in a big hall due to multiple reflections.

11.5 Applications of Ultrasound

Frequencies above 20 kHz are called Ultrasound. Used in:

  • Cleaning industrial parts.
  • Detection of cracks in metal blocks.
  • Medical imaging (Echocardiography, Ultrasonography).
  • SONAR: Sound Navigation and Ranging for underwater measuring.

Range of Hearing

Average human hearing range: 20 Hz to 20,000 Hz.

  • Infrasonic: Below 20 Hz (e.g., Rhinos, Whales).
  • Ultrasonic: Above 20 kHz (e.g., Bats, Dolphins).