Ncert science solutions class 9 Solutions for Chapter 12 sound

Exercises in Chapter 12 sound Grade 9

Sound - Exercise

Sound - Exercise 12.1

Sound - Exercise 12.2

Sound - Exercise 12.3

Questions in Sound - Exercise

What is sound and how is it produced?

Describe with the help of a diagram, how compressions and rarefactions are produced in the air near a source of the sound.

Why sound wave is called a longitudinal wave?

Which characteristics of the sound help you to identify your friend by his voice while sitting with others in a dark room?

Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?

Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in the air and in aluminium to reach the second child.

Does sound follow the same laws of reflection as light does? Explain.

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 m $s^{-2}$ and speed of sound = 340 m $s^{-1}$ .

A sound wave travels at a speed of 339 m $s^{-1}$ . If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

What is reverberation? How can it be reduced?

What is loudness of sound? What factors does it depend on?

Explain how bats use ultrasound to catch prey.

How is ultrasound used for cleaning?

Explain the working and application of a sonar.

A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.

Explain how defects in a metal block can be detected using ultrasound.

Explain how the human ear works.

Questions in Sound - Exercise 12.1

How does the sound produced by a vibrating object in a medium reach your ear?

Questions in Sound - Exercise 12.2

Explain how sound is produced by your school bell.

Which wave property determines (a) loudness, (b) pitch?

Why are sound waves called mechanical waves?

What are wavelength, frequency, time period and amplitude of a sound wave?

A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?

Questions in Sound - Exercise 12.3

Why are the ceilings of concert halls curved?