General Science Question Answers Chapter 15 Sound Class 8 Maharashtra Board

Question Answers For All Chapters – General Science Class 8

Exercise

1. Fill in the blanks with appropriate words:

(a) The region in a sound wave with higher pressure and density is called compression, and the region with low pressure and density is called rarefaction.

(b) Medium is necessary for the generation of sound.

(c) The total number of compressions and rarefactions per second in a sound wave is 1000, so the frequency of the sound wave is 1000 Hz.

(d) Different sound notes have different frequencies.

(e) In a loudspeaker, electrical energy is converted into sound energy.

2. Give Scientific Reasons:

(a) It is essential to change the tension on the vocal cords, as we produce different sound notes from our larynx.

• The tightness and thickness of the vocal cords control the pitch of sound.
• Tight cords produce high-pitched sounds, while loose cords produce low-pitched sounds.

(b) Astronauts on the moon can not hear each other directly

• Sound needs a medium like air, water, or solid to travel.
• Since there is no air on the moon, sound cannot travel, and astronauts use radio communication.

(c) As the sound wave propagates from one place to the other in air, the air itself is not required to move from one place to the other.

• In sound waves, air molecules only vibrate back and forth in their position.
• Only the pattern of compression and rarefaction moves, carrying the sound energy.

3. How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation?

• In a guitar, different sound notes are produced by changing the tension and length of the vibrating strings.
• In a flute, sound notes change when air passes through different hole positions, altering the length of the vibrating air column.

4. How is sound produced in the human larynx and a loudspeaker?

• In humans, sound is produced in the larynx (voice box). Air from the lungs vibrates the vocal cords, producing sound.
• In a loudspeaker, a coil and magnet vibrate, moving the attached screen back and forth, creating sound waves.

5. Explain the experiment, with a diagram, to prove the following : “Sound needs a material medium for propagation.”

Experiment using a Bell Jar:

1. Take an electric bell inside a vacuum jar and connect it to a power source.
2. Initially, with air inside, the bell rings, and we can hear the sound.
3. As air is removed using a vacuum pump, the sound becomes weaker.
4. When all air is removed, the sound completely stops, proving that sound needs a medium to travel.

6. Match the Following: