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Chapter Analysis
Intermediate12 pages • EnglishQuick Summary
The chapter on Sound in Class 9 Science explains how sound is produced, its propagation as a wave, and its characteristics, including frequency, wavelength, etc. It details the reflection of sound, applications of echo, and the concepts of loudness and intensity. The chapter also covers applications of sound, including ultrasound in medical and industrial fields.
Key Topics
- •Production and propagation of sound
- •Characteristics of sound waves
- •Reflection of sound
- •Applications of echo
- •Loudness and intensity
- •Range of hearing
- •Applications of ultrasound
Learning Objectives
- ✓Understand how sound is produced and propagated
- ✓Identify the properties of sound waves, such as frequency and amplitude
- ✓Explain the phenomenon of echo and its uses
- ✓Differentiate between loudness and intensity
- ✓Explore the range of human hearing and sounds beyond it
- ✓Learn about practical uses of ultrasound in various fields
Questions in Chapter
What is sound and how is it produced?
Page 138
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
Page 138
Why is sound wave called a longitudinal wave?
Page 138
Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Page 138
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Page 138
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.
Page 139
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.
Page 139
The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Page 139
Does sound follow the same laws of reflection as light does? Explain.
Page 139
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 remain the same. Do you hear echo sound on a hotter day?
Page 139
Give two practical applications of reflection of sound waves.
Page 139
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.
Page 139
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?
Page 139
What is reverberation? How can it be reduced?
Page 139
What is loudness of sound? What factors does it depend on?
Page 139
How is ultrasound used for cleaning?
Page 139
Explain how defects in a metal block can be detected using ultrasound.
Page 139
Additional Practice Questions
Explain the difference between frequency and amplitude in sound waves.
mediumAnswer: Frequency refers to how often the particles of the medium vibrate when a wave passes through the medium. It is measured in hertz (Hz). Amplitude is the maximum displacement of particles from their mean position. It determines the loudness of sound.
Why can't sound travel through a vacuum?
easyAnswer: Sound requires a medium to travel because it is caused by vibrations that need particles to propagate through. In a vacuum, there are no particles to carry the sound waves.
What happens to the speed of sound as the temperature of air increases?
mediumAnswer: The speed of sound in air increases as the temperature increases. This is because warmer air has particles that are moving faster, which facilitates the quicker transfer of wave energy.
Describe how ultrasound is used in medical imaging.
hardAnswer: Ultrasound in medical imaging is used by sending high-frequency sound waves into the body. The waves bounce back when they hit different tissues and these reflections are used to create an image of structures inside the body.
How is the pitch of a sound determined?
easyAnswer: The pitch of a sound is determined by its frequency. High-frequency sounds have a high pitch, while low-frequency sounds have a low pitch.
NCERT Exemplar
AvailablePractice with NCERT Exemplar problems and solutions for this chapter. Exemplar problems are designed to help you master the concepts with advanced-level questions.
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