NCERT solutions Science Textbook for Class 9 chapter 12 Sound



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Chapter 12 - Sound

Page 162

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

Q 1 | Page 162 | view solution

Page 163

Explain how sound is produced by your school bell.

Q 1 | Page 163 | view solution

Why are sound waves called mechanical waves?

Q 2 | Page 163 | view solution

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

Q 3 | Page 163 | view solution

Page 166

How are the wavelength and frequency of a sound wave related to its speed?

Q 2 | Page 166 | view solution

Page 167

In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?

Q 1 | Page 167 | view solution

Page 168

An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s−1?

Q 1 | Page 168 | view solution

Page 169

Why are the ceilings of concert halls curved?

Q 1 | Page 169 | view solution

Page 170

What is the audible range of the average human ear?

Q 1 | Page 170 | view solution

What is the range of frequencies associated with Infrasound?

Q 2.1 | Page 170 | view solution

What is the range of frequencies associated with Ultrasound?

Q 2.2 | Page 170 | view solution

Page 172

A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?

Q 1 | Page 172 | view solution

Pages 174 - 175

What is sound and how is it produced?

Q 1 | Page 174 | view solution

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

Q 2 | Page 174 | view solution

Cite an experiment to show that sound needs a material medium for its propagation.

Q 3 | Page 174 | view solution

Why is sound wave called a longitudinal wave?

Q 4 | Page 174 | view solution

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

Q 6 | Page 174 | view solution

A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 m s−1.

Q 7 | Page 174 | view solution

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 air and in aluminium to reach the second child.

Q 8 | Page 174 | view solution

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

Q 10 | Page 174 | view solution

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?

Q 11 | Page 174 | view solution

Give two practical applications of reflection of sound waves.

Q 12 | Page 174 | view solution

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.

Q 13 | Page 174 | view solution

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?

Q 14 | Page 174 | view solution

What is reverberation? How can it be reduced?

Q 15 | Page 175 | view solution

Explain how bats use ultrasound to catch a prey.

Q 17 | Page 175 | view solution

How is ultrasound used for cleaning?

Q 18 | Page 175 | view solution

Explain the working and application of a sonar.

Q 19 | Page 175 | view solution

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.

Q 20 | Page 175 | view solution

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

Q 21 | Page 175 | view solution

Explain how the human ear works.

Q 22 | Page 175 | view solution

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