Sound: Energy, Production, and Propagation

Sound is an energy form that creates hearing sensations and follows the law of conservation of energy, transforming from one type to another without being created or destroyed. It originates from vibrating objects, causing air particles to disturb and transfer energy until it reaches the ear. Sound propagates as waves through a chain reaction of particle disturbances.

Types of Waves (Based on Medium)

• Waves are of two types based on the requirement of a medium: mechanical and electromagnetic.
• Mechanical Waves: Require a medium for propagation (e.g., air, water, solid).
• Electromagnetic Waves: Don't require a medium for travel (e.g., light, radio waves).

Mechanical vs. Electromagnetic Waves

• Mechanical waves need a medium, while electromagnetic waves do not.
• Sound waves fall under the category of mechanical waves.
• Light waves are electromagnetic, hence sunlight reaches Earth through the vacuum of space.

Types of Waves (Based on Particle Motion)

• Based on particle motion, waves are either transverse or longitudinal.
• Transverse Waves: Particles move perpendicularly to the wave's direction.
• Longitudinal Waves: Particles' motion is parallel to the wave's direction.

Transverse Waves

• Particles move at right angles to the direction of the wave.
• These waves have crests (highest points) and troughs (lowest points).
• Light serves as an example of a transverse wave.

Longitudinal Waves

• Particles move in the same direction as the wave.
• Characterized by compressions (high pressure) and rarefactions (low pressure).
• Sound is a longitudinal wave.

Remembering Wave Types

• Use "PT Sir said SLEEP Later" to remember wave movement.
• PT: Perpendicular Transverse waves.
• SLEEP: Straight Longitudinal waves.

Sound Waves as Longitudinal Waves

• Sound waves are longitudinal, with particles vibrating along the wave's direction.
• Sound propagates through compressions and rarefactions.
• Compression occurs when air particles are forced together under high pressure.
• Rarefaction is when air particles expand under low pressure.

Characteristics of Sound Waves

• Frequency and time period are key characteristics.
• Frequency: The number of oscillations per second of a wave as it passes a fixed point.
• Measured in Hertz (Hz).
• Higher frequency results in a higher-pitched sound.
• Time Period: The duration of one complete oscillation.
• Measured in seconds.

Relationship Between Time Period and Frequency

• Time period (T) is inversely proportional to frequency (f): T = 1/f.
• Higher frequency corresponds to a lower time period, and vice versa.

Amplitude

• Amplitude is the maximum displacement of a particle from its resting position.
• It determines the loudness.

Wavelength

• Wavelength is the distance between two crests or troughs for transverse waves.
• For longitudinal waves, it's the distance between two compressions or rarefactions.
• Represented by lambda (λ), with meters as its SI unit.

Wave Speed

• Speed is the rate at which a wave travels.
• Wave speed (v) is calculated as v = wavelength (λ) x frequency (ν).

Factors Affecting Speed of Sound

• The medium affects the speed of sound.
• Sound travels faster in high-density media (solids) compared to low-density media (gases).
• Temperature influences sound speed.

The Flash-Bang Phenomenon

• Light travels faster than sound; lightning is seen before thunder is heard.
• Light's speed is 3 x 10^8 m/s, and sound's speed is about 330 m/s.

Super Sonic Speed

• Speed faster than the speed of sound.

Characterising "Sonic Boom"

• Sharp, loud sound generated when an object creates a shock wave.

Reflection of Sound

• Defined as the bending of sound waves.
• Sound waves follow two laws:
  • Incident, reflected sound, and the normal line lie on the same plane.
  • The reflected angle are equivalent.

Key Phenomenon

• Sound wave properties: echo, reflection, and reverberation.
• Echo: Sound heard again from a single reflection back to the source, which must be 17.2 meters away from the reflecting surface.
• Reverberation: Persistency of sound from repeated deflections off walls and ceilings, creating a long-lasting sound in the surroundings.

Addressing Reverberation

• Use sound-absorbent materials to minimize disturbance.
• Sound-absorbent materials include walls, carpets, and seats.

Additional Sound Phenomenon

• Multiple reflections are beneficial in megaphones for shouting to a larger audience and in stethoscopes.
  • Curved ceilings in auditoriums bounce back sound.

Additional Sound Phenomenon

• Audible Sound: The frequency range humans can hear, from 20 Hz to 20,000 Hz.

More Sound Phenomena

• Infrasound: Frequencies below 20 Hz.
• Ultrasound: Frequencies above 20,000 Hz.

Application when using Ultrasound

• Ultrasound cleans electronic components.
• It detects cracks in blocks, buildings, and metal by measuring waves.
• Heart conditions are measured by checking the heart rhythm.
  • Ultrasonography is used.
  • It's used to destroy kidney stones.

The "SONAR" System

• A sound navigation tool with a transmitter and detector to measure objects.
• Sound frequency bounces back and is measured to provide distance and location.
• Used to measure objects from boats and ships or for navigation by bats.