SSC CGL - Detailed Guide 2025
Self-Paced Course
Sound
Reference: NCERT Class 9-12, Lucent GK
1. Nature of Sound Waves
- Sound is a mechanical wave that requires a medium (solid, liquid, or gas) for propagation.
- Sound cannot travel through vacuum. It needs particles to transfer energy.
| Property | Details |
|---|---|
| Type of Wave | Longitudinal (particles oscillate parallel to wave) |
| Transmission Medium | Cannot travel in vacuum |
| Wave Features | Consists of compressions (high pressure) and rarefactions (low pressure) |
2. Speed of Sound
- Speed of sound depends on the medium's density and elasticity.
- Sound travels fastest in solids, slower in liquids, and slowest in gases.
- Speed increases with temperature.
- Speed in air is less than in water or metal.
| Medium | Approx. Speed at Room Temp |
|---|---|
| Air | 343 m/s (at 20°C) |
| Water | ~1500 m/s |
| Iron | ~5000 m/s |
3. Pitch, Frequency, and Amplitude
| Concept | Definition | Unit | Notes |
|---|---|---|---|
| Frequency (f) | Number of oscillations per second | Hertz (Hz) | More frequency → higher pitch (shrill sound) |
| Amplitude (A) | Maximum displacement from mean position | meters (m) | Greater amplitude → louder sound |
| Pitch | How high or low a sound is perceived | — | Depends on frequency |
| Loudness | Perceived intensity of sound | Decibel (dB) | Loudness ∝ Amplitude² |
| Time Period (T) | Time for one complete oscillation | Seconds (s) | T = 1 / f |
- Humans can hear frequencies between 20 Hz to 20,000 Hz (called audible range)
- < 20 Hz → Infrasonic | > 20,000 Hz → Ultrasonic
4. SONAR (Sound Navigation and Ranging)
- A technique to detect underwater objects using reflected ultrasonic waves.
- Used by ships, submarines, and for ocean bed mapping.
| Feature | Description |
|---|---|
| Principle | Echo (reflection of sound) |
| Components | Transmitter and Receiver |
| Medium | Water (mainly used in submarines, sea-depth measuring) |
| Distance Formula | Distance = (Speed × Time) / 2 (as it's a round trip) |
5. Doppler Effect
- Apparent change in frequency of sound due to relative motion between source and observer.
- Also observed in light and other wave phenomena.
- Example : Pitch of a siren increases as it approaches and drops after passing.
| Scenario | Apparent Frequency Change |
|---|---|
| Source approaching observer | Frequency increases |
| Source moving away | Frequency decreases |
Developed By Satyam Kumar
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