Sound Waves and Energy Transfer

Sound Waves

• Sound is a type of energy perceived as auditory sensations, resulting from vibrations propagating through a medium (air, liquids, solids).
• Vibrations cause pressure changes in the medium, forming sound waves.
• Sound needs a medium to travel; it cannot travel in a vacuum.

Key Aspects of Sound

• Vibration: Sound originates from a vibrating source (vocal cords, guitar strings, etc.) which sets molecules in the surrounding medium in motion.
• Medium: Sound requires a medium to travel through (air, water, etc.). Sound cannot travel in a vacuum (e.g., space).
• Sound Waves: Vibrations create compressions (molecules closer together) and rarefactions (molecules further apart) in the medium, forming a repeating pattern.

Waves

• Waves are a fundamental concept describing energy transfer through a medium without the actual movement of particles.
• There are two main types:
  • Transverse waves: Particle motion is perpendicular to wave direction (e.g., light waves, water waves).
  • Longitudinal waves: Particle motion is parallel to wave direction (e.g., sound waves).

Sound Wave Characteristics

• Wavelength: Shortest distance over which the wave pattern repeats. Represented by the Greek letter lambda (λ). Measured in meters. Combined length of compression and rarefaction.
• Amplitude: Maximum displacement of particles from their resting positions. Higher amplitude = louder sound. Measured in meters.
• Frequency: Rate at which waves are produced. Measured in Hertz (Hz). Higher frequency = higher pitch.

Speed of Sound

• The speed of sound depends on the medium. It travels faster in solids, then liquids, and slowest in gases.
• Factors influencing speed of sound in a medium include: Nature of medium (density and elasticity), Temperature, Humidity, Pressure, altitude, frequency. Denser, more elastic materials transmit sound faster. Air temperature increase, sound speed also increases.

Reflection of Sound

• Sound can reflect off surfaces. Reflection is governed by same principles as light reflection.
• Angle of incidence = angle of reflection.
• Echo: A reflected sound. A delay occurs between the original sound and its reflected sound. Echoes occur due to the reflection of sound waves off a surface, leading to a delayed repetition of the original sound.
• For distinct echo, the minimum time interval must be at least 0.1 seconds.

Applications of Multiple Reflections/Reverberation and Echo

• Sonar: A technology using reflected sound waves for underwater navigation and object detection.
• Medical Diagnostics (Ultrasound): Generating sound waves to create images of internal body structures.
• Echolocation: Animals use reflected sound waves to navigate and locate prey.
• Sound Engineering: Multiple reflections are used in concert halls and recording studios to create specific reverberation effects.

Human Ear

• The human ear consists of three parts: outer ear, middle ear, and inner ear. Each part plays a role in the process of hearing.
• Outer ear: Collects & directs sound waves into the ear canal.
• Middle ear: Contains ossicles (tiny bones) that amplify vibrations and transmit them to the inner ear.
• Inner ear: Contains cochlea, a fluid-filled structure where sound vibrations are converted into electrical signals.

Inaudible Range

• Infrasound: Frequencies below 20 Hz; humans cannot hear but can have physiological effects.
• Ultrasound: Frequencies above 20 kHz; some animals can hear, used in medical imaging.