Study Materials

# NCERT Solutions for Class 8th Science

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## Chapter 13. Sound

Ques: What is sound?

Ans: When an object vibrates, it produces sound.

Ques: What is eco sound?

Ans: When any sound reflects by striking on any medium, that sound heard us again and again. This is called eco sound.

Ques: What is minimum audible range for human ears?

Ans: The audible range is 20 Hz to 20,000 Hz.

Ques: What is minimum audible distance from sound source to barrier medium?

Ans: 17.2 m.

Ques: What is S.I unit of frequency?

Ans: Hz (Hertz).

Ques: What is S.I unit of wave length?

Ans: S.I unit of wave length is meter.

Ques: By what organ human produces sound?

Ans: Vocal cord. (Larynx)

Ques: How do we produce sound?

Ans: Two vocal cords, are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air When the lungs force air through the slit, the vocal cords vibrate, producing sound.

Ques: In which mediums sounds propagate?

Ans: Solid, liquid and gas.

Ques: In which medium sound does not propagate?

Ans: Vacuum.

Ques: What is eardrum?

Ans: The shape of the outer part of the ear is like a funnel. When sound enters in it, it travels down a canal at the end of which a thin membrane is stretched tightly. It is called the eardrum.

Ques: Write the function of eardrum.

Ans: The eardrum sends vibrations to the inner ear.

Ques: What is oscillatory motion?

Ans: The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.

Ques: What is frequency? Write is its S.I unit?

Ans: The number of oscillations or vibrations per second is called the frequency of oscillation. The frequency is expressed in hertz (Hz).

Ques: On which measure does loudness of sound depend?

Ans: On its amplitudes.

Ques: What are two important properties of sound?

Ans: Amplitude and frequency are two important properties of any sound.

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