Page No 163: - Chapter 12 - Sound - Ncert Solutions class 9 - Science

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Question 1:

Explain how sound is produced by your school bell.

Answer:

When the school bell vibrates, it forces the adjacent particles in air to vibrate. This disturbance gives rise to a wave and when the bell moves forward, it pushes the air in front of it. This creates a region of high pressures known as compression. When the bell moves backwards, it creates a region of low pressure know as rarefaction. As the bell continues to move forward and backward, it produces a series of compressions and rarefactions. This makes the sound of a bell propagate through air.

Question 2:

Why are sound waves called mechanical waves?

Answer:

Sound waves force the medium particles to vibrate. Hence, these waves are known as mechanical waves. Sound waves propagate through a medium because of the interaction of the particles present in that medium.

Question 3:

Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

Answer:

Sound needs a medium to propagate. Since the moon is devoid of any atmosphere, you cannot hear any sound on the moon.