NCERT Class-9 Science Solutions: Chapter 12-Sound Part 2

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Question 8:

Infrasound can be heard by

  1. Dog

  2. Bat

  3. Rhinoceros

  4. Human beings

Answer: C

Image animal who can heared Infrasound

Image Animal Who Can Heared Infrasound

Image animal who can heared Infrasound

Question 9:

Before playing the orchestra in a musical concert, a satirist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting

  1. Intensity of sound only

  2. Amplitude of sound only

  3. Frequency of the sitar string with the frequency of other musical instruments

  4. Loudness of sound

Answer: C

Image frequency of other musical instruments

Image Frequency of Other Musical Instruments

Image frequency of other musical instruments

Short Answer Question

Question 10:

The given graph (Figure) shows the displacement versus time relation for a disturbance travelling with velocity of . Calculate the wavelength of the disturbance.

Image wavelength of the disturbance

Image Wavelength of the Disturbance

Image wavelength of the disturbance

Answer:

From the graph

Time period,

Frequency,

Wavelength,

Where,

Question 11:

Which of the above two graphs (a) and (b) (Figure) representing the human voice is likely to be the male voice? Give reason for your answer.

Image the wave disturbance - time graph

Image the Wave Disturbance - Time Graph

Image the wave disturbance - time graph

Answer:

Graph (a) represents the male voice. Usually the male voice has less pitch (or frequency) as compared to female.Male voice have generally lower pitch and hence lower frequency of sound. From the graph, wave "a" is likely to be of a male voice

Question 12:

A girl is sitting in the middle of a park of dimension . On the left side of it there is a building adjoining the park and on right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.

Answer:

If the time gap between the original sound and reflected sound received by the listener is around 0.1 s, only then the echo can be heard.

The minimum distance travelled by the reflected sound wave for the distinctly listening the echo

But in this case the distance travelled by the sound reflected from the building and then reaching to the girl will be , which is much smaller than the required distance. Therefore, no echo can be heard.