Question 9
List sources of noise pollution in your surroundings.
Sources of noise pollution are:
- Horn of vehicles
- Explosions including bursting of crackers
- Sounds from machines, loudspeakers
- Television, transistor and radio at high volumes
- Desert coolers, air conditioners
Chapter Overview: Sound
This chapter covers how sound is produced by vibrating objects, how it travels through media (solid > liquid > gas), and its characteristics: frequency (pitch), amplitude (loudness), and time period. The audible range, ultrasound applications, human ear anatomy, and noise pollution are important exam topics.
Board Exam Weightage: 5-7 marks | Difficulty: Moderate to High
Key Formulas & Concepts
| Concept | Details |
|---|---|
| Frequency | f = number of oscillations per second; Unit: Hertz (Hz) |
| Time Period | T = 1/f; Time for one complete oscillation; Unit: seconds |
| Audible Range | 20 Hz to 20,000 Hz (for humans) |
| Sound Speed | Solid (~5000 m/s) > Liquid (~1500 m/s) > Gas (~340 m/s in air at 20°C) |
Must-Know Concepts
- Sound is produced by vibrating objects and needs a medium to travel (cannot travel in vacuum)
- Loudness depends on amplitude; pitch depends on frequency
- Men have deeper voices because their vocal cords are longer (lower frequency)
- Ultrasound (>20,000 Hz): used in medical imaging (ultrasonography), SONAR, cleaning
- Infrasound (<20 Hz): produced by earthquakes, elephants, whales
- Noise pollution causes hearing loss, stress, high blood pressure; controlled by silencers, green belts, ear protection
Loudness vs Pitch
| Property | Loudness | Pitch |
|---|---|---|
| Depends on | Amplitude | Frequency |
| Greater → | Louder sound | Higher (shriller) sound |
| Unit | Decibel (dB) | Hertz (Hz) |
| Example | Shouting vs whispering | Woman's voice vs man's voice |
Common Mistakes to Avoid
- Confusing loudness (amplitude) with pitch (frequency)
- Thinking sound can travel through vacuum
- Errors in T = 1/f calculations (they are inversely related)
- Mixing up ultrasound (>20,000 Hz) and infrasound (<20 Hz)
Scoring Tips
- Practice T = 1/f problems: if f = 500 Hz, T = 0.002 s
- Draw and label the human ear with all parts
- Learn 3 applications each of ultrasound and noise prevention
- Remember: solid > liquid > gas for speed of sound
Frequently Asked Questions
Q: How many marks does this chapter carry in the exam?
A: Approximately 5-7 marks in the annual exam.
Q: What question types are commonly asked?
A: MCQs (1 mark), Very Short Answer (2 marks), Short Answer (3 marks), and Long Answer / Diagram (5 marks).
Q: Is this chapter important for competitive exams?
A: Yes, concepts from this chapter appear in NTSE, Olympiad, and other science competitions.