🌈 RAINBOW MIND MAP: SOUND
Class 9 – ICSE Physics
1. Sound and its Production
Sound is a form of energy that produces the sensation of hearing. It is produced due to vibrations of objects.
Examples: tuning fork, vocal cords, loudspeaker diaphragm, stretched string.
No vibration → no sound.
2. Sound Requires a Medium & Conditions of the Medium
Sound cannot travel in vacuum. It needs a material medium.
Conditions of the medium:
- Elasticity – to regain original position
- Inertia – mass of particles
- Very low friction – to avoid loss of energy
3. Sound as a Longitudinal Wave & Related Terms
Sound travels as a longitudinal wave. Particles vibrate parallel to the direction of propagation.
- Compression: region of high pressure and density
- Rarefaction: region of low pressure and density
- Wavelength (λ): distance between two successive compressions
- Frequency (f): number of vibrations per second
- Time Period (T): time taken for one vibration
4. Speed of Sound in Different Media & Factors Affecting It
Speed of sound:
- Maximum in solids
- Less in liquids
- Least in gases
Factors affecting speed in a medium:
- Density of the medium
- Elasticity of the medium
5. Factors Affecting & Not Affecting Speed of Sound in a Gas
Affected by:
- Density
- Temperature
- Humidity
- Direction of wind
Not affected by:
- Pressure
- Amplitude of the wave
- Wavelength or frequency of the wave
6. Comparison of Speed of Sound and Light
Speed of sound in air ≈ 330 m/s
Speed of light in vacuum ≈ 3 × 10⁸ m/s
Light travels much faster than sound. Hence, lightning is seen before thunder is heard.
7. Infrasonic, Sonic and Ultrasonic Waves
- Infrasonic: frequency < 20 Hz (earthquakes, elephants)
- Sonic (Audible): 20 Hz – 20,000 Hz (human hearing range)
- Ultrasonic: frequency > 20,000 Hz (SONAR, medical imaging, flaw detection)
💬 Think & Comment:
Why does sound travel faster in solids than in gases? Write your answer in the comments.
Why does sound travel faster in solids than in gases? Write your answer in the comments.
