Imp Questions For All Chapters – General Science Class 8
Short Questions
1. What is sound?
- Sound is a form of energy produced by vibrations.
2. What do sound waves need to travel?
- Sound needs a medium (solid, liquid, or gas) to travel.
3. Can sound travel in a vacuum?
- No, sound cannot travel in a vacuum because there are no particles to carry the vibrations.
4. What are compressions and rarefactions?
- Compression is a region of high pressure, and rarefaction is a region of low pressure in a sound wave.
5. What is the speed of sound in air?
- The speed of sound in air is 340 m/s.
6. In which medium does sound travel fastest?
- Sound travels fastest in solids, then in liquids, and slowest in gases.
7. What is frequency?
- Frequency is the number of sound waves passing a point per second.
8. What is the unit of frequency?
- Frequency is measured in Hertz (Hz).
9. What is pitch?
- Pitch tells us how high or low a sound is, based on its frequency.
10. What is loudness?
- Loudness is the strength of a sound, which depends on the amplitude of the sound wave.
11. What is the unit of loudness?
- Loudness is measured in Decibels (dB).
12. What is the function of the larynx in humans?
- The larynx (voice box) produces sound by vibrating the vocal cords.
13. What is an echo?
- An echo is a reflected sound wave that we hear again.
14. What is the minimum distance required for an echo?
- At least 17 meters is needed to hear an echo.
15. What is SONAR?
- SONAR (Sound Navigation and Ranging) is used in ships and submarines to measure ocean depth.
16. Why do bats use echolocation?
- Bats use sound waves to find food and move in the dark.
17. What are noise and music?
- Noise is an unpleasant sound, while music is a pleasant and rhythmic sound.
18. What is noise pollution?
- Noise pollution is excessive and harmful noise in the environment.
19. How can we reduce noise pollution?
- We can reduce noise pollution by soundproofing, reducing honking, and planting trees.
20. What are the three types of musical instruments?
- String instruments (guitar, violin), wind instruments (flute, trumpet), and percussion instruments (drums, tabla).
Long Questions
1. How is sound produced in humans?
- Sound is produced in the larynx (voice box) when air from the lungs vibrates the vocal cords. The tightness and length of the vocal cords control the pitch of the sound.
2. Why does sound travel fastest in solids?
- Sound travels fastest in solids because the particles are closely packed, allowing vibrations to pass quickly. In gases, the particles are far apart, so sound moves slower.
3. What is an echo, and how is it useful?
- An echo is a reflected sound that we hear again after bouncing off a surface. It is used in SONAR for measuring ocean depth and in medical ultrasound for imaging.
4. How does a loudspeaker produce sound?
- A coil and magnet inside the loudspeaker vibrate a diaphragm, creating sound waves. These vibrations travel through the air, allowing us to hear the sound.
5. What are the harmful effects of noise pollution?
- Noise pollution can cause hearing loss, stress, sleep problems, and heart disease. It also disturbs wildlife, reduces concentration, and affects mental health.
6. How do musical instruments produce sound?
- In string instruments, sound is made by vibrating strings, while in wind instruments, air vibrations create sound. Percussion instruments like drums produce sound when struck.
7. Why do we hear sound from a guitar when we pluck its strings?
- When we pluck a guitar string, it vibrates and produces sound waves in the air. The vibrations are amplified by the hollow wooden body of the guitar, making the sound louder.
8. Why can we not hear sounds on the Moon?
- The Moon has no air (vacuum), so there is no medium for sound to travel. Since sound needs air, water, or solids to move, astronauts must use radios to communicate.
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