To identify the different sound voices, the characteristics that help are timbre and pitch. Even if a person is sitting in a dark room with friends, they can identify different voices due to the difference in sound pitch and timbre.

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

Explain how defects in a metal block can be defected using ultrasound?

How is ultrasound used for cleaning?

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

What is reverberation? How can it be reduced?

A sound wave travels at a speed of 339 ms–1. If it’s wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

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 ms–2 and speed of sound = 340 ms–1.

Give two practical applications of reflection of sound waves?

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?

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

The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

Two children are at opposite ends of an aluminum 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 aluminum to reach the second child.

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 ms–1?

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

Why is sound wave called a longitudinal wave?

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

What is sound and how is it produced?

What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?

Why are the ceilings of concert halls curved?

An echo is heard in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms–1?

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

Distinguish between loudness and intensity of sound.

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?

Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

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

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

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

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

Why are sound waves called mechanical waves?

Explain how sound is produced N by your school bell.

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

Chapter 11 NCERT Class 9 Science SOLUTIONS

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