# Class 9th Science Solutions Chapter 12: Sound

Class 9th Science solutions Chapter 12: Sound NCERT Solutions for Class 9 Science Chapter 12 – Sound solved by Expert Teachers as per NCERT (CBSE) Book guidelines. These solutions are part of NCERT Solutions for Chapter 12 Science, Sound class 9. Here we have given Class 9 NCERT Science Textbook Solutions for Chapter 12  Sound class 9

## Class 9th Science solutions Chapter 12: Sound

1: How does the sound produced by a vibrating object in a medium reach your ear?
Answer: When a body vibrates the air in its neighborhood is alternately compressed and rarefied. The compressed air has a higher pressure than the surrounding air. It, therefore, pushes the air particles near it causing compression to move forward. A rarefaction or low pressure is created at the original place. These compressions and rarefaction cause particles in the air to vibrate about their mean position. The energy is carried forward in this vibration. This is how sound travels.

1: Explain how sound is produced by your school bell?
Answer: When the gong strikes the bell, vibrations are produced in the bell which is transmitted through the air to our ears. These vibration produce sensation of sound in our ears.

2: Why are sound waves called mechanical waves?
Answer: Sound waves are called mechanical waves because they need a material medium to travel.

3: Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer: On the moon, sound cannot travel as there is no atmosphere. Sound cannot travel in a vacuum so we will not be able to hear any sound.

1: Which waves property determines
(a) loudness (b) pitch?
a) Loudness is determined by the amplitude of the sound. Greater the amplitude
more will be the loudness.
b) Pitch is determined by frequency. Higher is the frequency, greater will be the
pitch.

2: Guess which sound has a higher pitch: guitar or car horn?

1: What are the wavelength, frequency, time period, and amplitude of a sound wave?
Answer: Wavelength: The distances between two consecutive compressions or rarefaction of a wave.
Its S.I unit is meter.
Frequency: One compression and one rarefaction constitute one vibration. The number of
vibration in a second is called frequency. Its unit is Hertz.
Amplitude: When waves are produced, the particles vibrate about their mean position. The
maximum displacement from its mean position of a particle is called its amplitude. It is
measured in meters.
Time period: The time taken by the wave to complete one oscillation i.e., the time between two consecutive compressions or rarefactions is called time period.

See Also:  NCERT Solutions for Class 9 Science Chapter 12 – Sound