10.1 Characteristics of Sound Waves
Sound is a form of energy produced by the vibration of objects. Sound travels through a medium in the form of longitudinal waves consisting of compressions and rarefactions.
Propagation of Sound
- Medium Requirement: Sound requires a medium (solid, liquid, or gas) to travel. Sound cannot travel through a vacuum because there are no particles to transmit vibrations.
- Speed of Sound: Depends on the arrangement and density of particles in the medium.
$$\text{Speed of Sound: } \text{Solids} > \text{Liquids} > \text{Gases}$$
- Sound travels fastest in solids because particles are packed closely together, transferring kinetic energy from particle collisions rapidly.
Reflection and Absorption of Sound
- Hard, Smooth Surfaces: Good sound reflectors (e.g., concrete walls, tiles, glass, metal sheets).
- Soft, Rough Surfaces: Good sound absorbers (e.g., curtains, carpets, sponges, wooden acoustic panels). Used in cinema halls and recording studios to reduce unwanted echoes.
10.2 Loudness and Pitch of Sound
Loudness and Amplitude
- Loudness: The intensity of sound as perceived by the human ear.
- Depends on wave Amplitude (maximum displacement of a particle from its rest position).
- High Amplitude $\rightarrow$ Loud Sound (carries more energy).
- Low Amplitude $\rightarrow$ Soft Sound (carries less energy).
- Measured in Decibels (dB).
Pitch and Frequency
- Pitch: The highness or lowness of a sound tone.
- Depends on wave Frequency (number of complete vibrations per second).
- SI Unit of Frequency: Hertz (Hz).
- High Frequency $\rightarrow$ High Pitch (shorter wavelength).
- Low Frequency $\rightarrow$ Low Pitch (longer wavelength).
10.3 Phenomena and Applications of Sound Waves
Echo
An echo is a sound heard again after being reflected off a hard, flat surface (such as a tall cliff or concrete wall). Echoes occur when the original and reflected sounds are heard as separate sounds.
Doppler Effect
The Doppler Effect is the apparent change in frequency or pitch of a sound caused by the relative motion between the sound source and the observer.
- Approaching Source: Frequency/pitch appears higher because sound waves are compressed together.
- Receding Source: Frequency/pitch appears lower because sound waves are spread further apart.
- Example: The changing pitch of an ambulance siren as it drives past a bystander.
Audio Frequency Limits
- Human Hearing Range: $20\text{ Hz}$ to $20,000\text{ Hz}$ ($20\text{ kHz}$).
- Infrasound: Frequencies below $20\text{ Hz}$ (audible to elephants and whales).
- Ultrasound: Frequencies above $20,000\text{ Hz}$ (audible to bats, dolphins, and dogs).
Applications of Ultrasound in Technology
- SONAR (Sound Navigation and Ranging): Uses ultrasonic reflections to measure ocean depth, map seabed topography, or locate submerged shipwrecks and fish shoals.
- Medical Imaging: Ultrasonic scans produce images of internal organs or developing fetuses safely without harmful ionizing radiation.
- Industrial Cleaning: High-frequency ultrasound vibrations dislodge microscopic dirt from delicate jewelry and electronic components.