NCERT Exemplar solutions for Science [English] Class 9 chapter 12 - Sound [Latest edition]

Note is a sound

A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case

In SONAR we use:

Sound travels in the air if

When we change feeble sound to loud sound we increase its

In the curve (Fig.12.1) half the wavelength is

An earthquake produces which kind of sound before the mainshock wave begins

Infrasound can be heard by

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

The given graph (Fig.12.2) shows the displacement versus time relation for a disturbance travelling with a velocity of 1500 ms^–1. Calculate the wavelength of the disturbance.

Which of the above two graphs (a) and (b) (Fig.12.3) representing the human voice is likely to be the male voice? Give a reason for your answer.

A girl is sitting in the middle of a park of dimension 12 m × 12 m. On the left side of it, there is a building adjoining the park and on the 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.

Why do we hear the sound produced by the humming bees while the sound of vibrations of the pendulum is not heard?

If any explosion takes place at the bottom of a lake, what type of shock waves in water will take place?

The sound produced by a thunderstorm is heard 10 s after the lightning is seen. Calculate the approximate distance of the thunder cloud. (Given the speed of sound = 340 m s^–1.)

For hearing the loudest ticking sound heard by the ear, find the angle x in Fig.12.4.

Why is the ceiling and wall behind the stage of good conference halls or concert halls made curved?

Represent graphically by two separate diagrams in each case 

Two sound waves having the same amplitude but different frequencies?

Represent graphically by two separate diagrams in each case 

Two sound waves have the same frequency but different amplitudes.

Represent graphically by two separate diagrams in each case

Two sound waves have different amplitudes and also different wavelengths.

Establish the relationship between the speed of sound, its wavelength and frequency. If the velocity of sound in air is 340 m s^–1, calculate

(i) wavelength when the frequency is 256 Hz.

(ii) frequency when the wavelength is 0.85 m

Draw a curve showing density or pressure variations with respect to distance for a disturbance produced by sound. Mark the position of compression and rarefaction on this curve. Also, define wavelengths and time periods using this curve.