CG SCERT (Chhattisgarh Board) Class 8 Science & Technology Solutions | 2026-27 Official Edition
Welcome to the complete, 100% textbook-grounded CG Board Class 8 Science Chapter 10 Solutions: Sound (ध्वनि) in Bilingual Format (English Medium + हिंदी माध्यम). Every in-text question (Answer these / इनके उत्तर दीजिए) and end-of-chapter exercise (Exercises / अभ्यास के प्रश्न) has been solved strictly from the official 2026-27 SCERT Chhattisgarh Raipur textbook.
End-of-Chapter Exercises (Solutions)
अभ्यास के सभी प्रश्नों के हल
(1) The range of audible frequencies for human beings is: (a…
अभ्यास प्रश्न
(1) The range of audible frequencies for human beings is:
(a) 0 – 20 Hertz
(b) 20 – 2000 Hertz
(c) 0 – 20,000 Hertz
(d) 20 – 20,000 Hertz
- Answer:(d) 20 – 20,000 Hertz
(2) On increasing the frequency of a sound, what else increases:
(a) Its pitch
(b) Its intensity
(c) Its time period
(d) Its amplitude
- Answer:(a) Its pitch
(3) To hear the echo clearly, the minimum distance of the reflecting surface should be:
(a) 11 metre
(b) 34 metre
(c) 17 metre
(d) 50 metre
- Answer:(c) 17 metre
(4) Sound propagation is not possible:
(a) In metals
(b) In water
(c) In vacuum
(d) In air
- Answer:(c) In vacuum
Write the definitions of amplitude and frequency
आयाम Amplitude कंपित वस्तु का अपनी मध्यमान मूल…
Amplitude:** The maximum displacement of a vibrating body from its mean (central) position is called its amplitude. Its S.I. unit is metre (m).
- Frequency: The total number of vibrations or oscillations completed by a vibrating object in one second is called its frequency. Its S.I. unit is Hertz (Hz).
How would you show through an experiment that…
योग व्यवस्था एक काँच का जार लेते हैं…
Experiment Setup:** Take an airtight glass jar fitted with an electric bell inside it and connected to a vacuum pump at the bottom.
- Procedure:
- Initially, when air is present inside the jar, press the bell switch. The sound of the ringing bell is clearly heard outside. This shows that sound propagates through air (gas).
- Now, gradually pump out the air from inside the jar using the vacuum pump.
- Observation: As the air is removed, the sound of the bell becomes fainter and fainter, until it completely stops when a vacuum is created, even though the hammer is still seen striking the bell.
- Conclusion: This experiment proves that gas (air) is a medium through which sound propagates, and sound cannot travel in a vacuum.
Differentiate between a noise and a melodious sound
लक्षण सुरीली ध्वनि संगीत शोर Noise 1 कानों…
| Feature | Melodious Sound (Music) | Noise |
|---|---|---|
| 2. Nature of Vibrations | Produced by regular and harmonious vibrations. | Produced by irregular and non-harmonious vibrations. |
| 3. Health Impact | Does not cause mental stress or health damage. | Causes irritation, headache, and noise pollution. |
| 4. Examples | Sound from sitar, flute, violin, or sweet singing. | Sound of heavy traffic, gunshots, or loud horns. |
Sound is heard clearly in a big room…
बिना पर्दे वाले खाली बड़े कमरे की कठोर…
In a big empty room without curtains, the hard bare walls act as good reflectors of sound. Sound reflects repeatedly from the walls, producing multiple echoes and reverberations that overlap with the original sound, making it indistinct and unclear.
- In contrast, when curtains (made of cloth/fabric) are hung on the walls, they act as good sound absorbers. The curtains absorb the reflected sound waves instead of bouncing them back, preventing echoes and allowing the original sound to be heard cleanly and clearly.