NCERT Class 9 Sciences Chapter 12 SOUND Notes
NCERT Class 9 Sciences Chapter 12 SOUND Notes
Introduction to Waves:
- Wave: disturbance in a medium carrying energy without net particle movement.
- Types: Transverse (perpendicular particle motion), Longitudinal (parallel particle motion).
Particle Motion of Mechanical Waves:
- Transverse Waves: Particle motion perpendicular to wave motion.
- Example: Light, Mexican wave.
- Longitudinal Waves: Particle motion parallel to wave motion via compressions or elongations.
- Example: Sound waves in air.
Sound Properties:
- Introduction to Sound Waves:
- Sound needs a medium.
- Propagates through compressions and rarefactions.
Characteristics:
- Wavelength (λ), Time period (T), Frequency (𝛎).
- Speed (v) related as v=λ𝛎.
- Amplitude (A), Pitch (directly proportional to frequency), Volume (related to amplitude).
- Note and Tone: Tone (single frequency), Note (mixture of frequencies).
- Quality of Sound: Richness or timber.
- Speed of Sound: Depends on medium properties: pressure, density, temperature.
- Speed hierarchy: Solids > Liquids > Gases.
- Speed in air: 331 m/s at 0°C, 344 m/s at 22°C.
- Sonic boom: Sound speed exceeded, producing shockwaves.
Reflection of Sound Waves:
- Follows laws of reflection, bouncing off surfaces.
- Echo: Sound reflected, heard again.
- Requirements: Time interval ≥ 0.1s, minimum obstruction distance = 17.2m.
Sonar and Radar:
- SONAR: Sound Navigation And Ranging.
- Uses ultrasonic waves.
- Applications: Imaging, detecting objects underwater.
- Ultrasonic Sounds: Frequencies > 20kHz.
- Applications: Medical imaging, object detection.
- Reverberation: Persistence of sound due to multiple reflections.
- Examples: Auditoriums, halls.
- Doppler’s Effect: Change in frequency and wavelength due to motion.
- Example: Ambulance siren.
Human Ear:
- Sensitive organ for sound detection, transmission, balance.
- Components: Outer ear (pinna), auditory canal, eardrum, middle ear (hammer, anvil, stirrup), inner ear (cochlea, auditory nerve).
Post a Comment