SOUND

Science

1. INTRODUCTION
• Sound is a form of energy that produces the sensation of hearing in our ears.
• It is produced due to vibration of objects.
• Sound needs a material medium for propagation.
• Sound cannot travel in vacuum.

2. PRODUCTION OF SOUND
• Sound is produced when an object vibrates.
• Vibrating objects set the surrounding particles into vibration.
• These vibrations are transmitted through the medium.
Examples:
• Vibrating tuning fork
• Vibrating vocal cords
• Vibrating guitar strings
• Vibrating diaphragm of a loudspeaker

3. PROPAGATION OF SOUND
• Sound propagates in the form of mechanical waves.
• It travels through a medium by the process of compression and rarefaction.
• Compression: Region of high pressure and high density.
• Rarefaction: Region of low pressure and low density.
• Particles of the medium do not move from source to listener; only energy is transferred.

4. SOUND WAVES
• Sound waves are longitudinal waves.
• In longitudinal waves, particles vibrate parallel to the direction of wave propagation.
• Sound cannot travel as transverse waves in air.

5. MEDIUM OF SOUND
• Sound can travel through solids, liquids and gases.
• Speed of sound is maximum in solids, less in liquids and minimum in gases.
Order:
Solids > Liquids > Gases

6. SPEED OF SOUND
• Speed of sound depends on:
- Nature of medium
- Temperature
- Humidity (in air)
• Speed of sound in air at 25°C ≈ 346 m/s
• Sound travels faster in warm air than in cold air.

7. CHARACTERISTICS OF SOUND

(a) Amplitude
• Maximum displacement of particles from mean position.
• Determines loudness of sound.
• Greater amplitude → louder sound.

(b) Time Period (T)
• Time taken to complete one vibration.
• Unit: second (s)

(d) Relationship:
f = 1 / T

(e) Wavelength (λ)
• Distance between two consecutive compressions or rarefactions.
• Unit: metre (m)

(f) Velocity of Sound (v)
• Distance travelled per unit time.
• v = f × λ

8. LOUDNESS AND INTENSITY
• Loudness depends on amplitude and sensitivity of ear.
• Intensity is sound power per unit area.
• Loudness is subjective; intensity is objective.
• Unit of intensity: watt per square metre (W/m²)

9. DECIBEL SCALE
• Loudness is measured in decibel (dB).
Examples:
• Whisper: ~20 dB
• Normal conversation: ~60 dB
• Traffic noise: ~80–90 dB
• Pain threshold: ~120 dB

10. AUDIBLE AND INAUDIBLE SOUNDS
• Audible range for humans: 20 Hz – 20,000 Hz
• Infrasonic sound: Frequency less than 20 Hz
- Example: Earthquakes, elephants
• Ultrasonic sound: Frequency greater than 20,000 Hz
- Example: Bats, dolphins

11. ULTRASOUND AND ITS APPLICATIONS
• Ultrasound uses high frequency sound waves.
Applications:
• Medical imaging (Ultrasonography)
• Detecting cracks in metal blocks
• SONAR for underwater navigation
• Cleaning delicate electronic components
• Kidney stone treatment (lithotripsy)

12. ECHO
• Echo is the repetition of sound due to reflection.
• Minimum distance for echo: 17 metres.
• Time gap between original sound and echo ≥ 0.1 second.

13. REVERBERATION
• Persistence of sound due to multiple reflections.
• Excessive reverberation causes noise.
• Controlled using sound-absorbing materials.

14. SONAR (Sound Navigation and Ranging)
• Used to detect underwater objects.
• Works on principle of echo.
Uses:
• Depth measurement of sea
• Locating submarines
• Fish finding

15. REFLECTION OF SOUND
• Sound reflects from hard surfaces.
• Laws of reflection of sound are similar to light.

16. ABSORPTION OF SOUND
• Soft and porous materials absorb sound.
Examples:
• Curtains
• Carpets
• Acoustic panels

17. NOISE AND NOISE POLLUTION
• Noise is unwanted sound.
• Noise pollution causes:
- Hearing loss
- Stress
- Sleep disturbance
- Hypertension
Control measures:
• Use of silencers
• Sound barriers
• Proper urban planning
• Limiting loudspeaker use

18. HUMAN EAR
Parts:
• Outer ear – collects sound
• Middle ear – amplifies vibrations
• Inner ear – converts vibrations to nerve signals
• Auditory nerve carries signals to brain

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Subject: Science

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