Question 7
Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
(a) Dholak — Stretched membrane.
(b) Sitar — Stretched strings
(c) Flute — Air column
Key Concepts Covered
This question tests your understanding of the following concepts from the chapter Sound: Question, Part, Vibrates, Produce, Sound, Instruments. These are fundamental topics in Science that students are expected to master as part of the CBSE Class 8 curriculum.
A thorough understanding of these concepts will help you answer similar questions confidently in your CBSE examinations. These topics are frequently tested in both objective and subjective sections of Science papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This Question
Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to Remember
- Read the question carefully and identify all parts before answering.
- Use the terminology specific to this subject and chapter.
- Review the textbook content for this chapter before attempting questions.
- Practice writing concise, well-structured answers within time limits.
Practice more questions from Sound — Science, Class 8 CBSE
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.