NCERT Solutions Class 9 Science Chapter 11 Sound - PDF Download

11.1 Production of Sound: The production of sound is the production of mechanical vibrations, or waves, which travel through a medium such as air and are perceived by the human ear as auditory experiences. The production of sound can take place through a variety of sources, including vibrating objects, acoustic instruments, electronic devices, human voice, etc.

11.2 Propagation of Sound: The propagation of sound is a process in which mechanical waves are transmitted through a medium, usually air, but also solids and liquids, in a manner that involves the transfer of energy between two points without the transfer of mass.

Subtopics covered in the section 11.2 Propagation of Sound:

11.2.1 Sound waves are longitudinal waves

11.2.2 Characteristics of a sound wave

11.2.3 Speed of sound in different media

11.3 Reflection of Sound: When sound waves bounce off a surface or something and change direction. It's similar to how light reflects off a mirror. The law of reflection says that the angle at which a sound wave hits the surface is the same as the angle at which it bounces off the surface.

Subtopics covered in the section 11.3 Reflection of Sound:

11.3.1 Echo

11.3.2 Reverberation 

11.3.3 Uses of multiple reflection of sound

11.4 Range of Hearing: The audible frequency range, or audible spectrum, is the frequency or pitch range that the average person's ears can pick up on and hear as sound. People's hearing range can be different, but it's usually between 20 Hertz (20 Hz) and 20,000 Hertz (20 kHz).

11.5 Applications of Ultrasound: Ultrasounds or ultrasonic waves are high frequency waves that travel along well defined paths, even when there are obstacles in the way. They are widely used in industry, medical purposes, clean parts located in hard to reach places, detect cracks and flaws in metal blocks etc.

Key Features of Class 9 Science Chapter 11 

• Vibrations of various objects produce sound.

• Sound travels as longitudinal waves through a medium.

• Sound travels through successive compressions or rarefactions in the medium.

• When sound travels through a medium, it travels as energy, not particles.

• When the density changes from one highest value to the minimum value and back to the maximum value, one complete oscillation occurs.

• The distance between consecutive compressions or consecutive rarefactions is known as the wavelength.

• The time taken by a wave for a complete oscillation of the density or pressure in the medium is known as the time period, T.

• The speed of sound (v = λ) is related to the frequency ν and the wavelength λ. The speed depends mainly on the nature of the sound and the temperature of the medium being transmitted.

• The law of reflection states that the direction in which the sound is reflected and the direction in which it is incident are at the same angles with the normal of the reflecting surface (at the point of incidence) and that the three are in the plane of each other.

• For a distinct sound to be heard, there must be a time interval of at least 0.1 s between the original and reflected sound.

• The presence of sound in the auditorium is caused by repeated reflections of sound, and is known as reverberation.

Benefits of Downloading the PDF of NCERT Solutions Class 9 Science Chapter 11 Sound 

Downloading PDFs of NCERT solutions for class 9 science chapter 11, which deals with sound, can provide several advantages for students learning this subject. Some of the advantages include:

• NCERT Solutions provide a wide variety of practice questions and exercises. Download the PDF to have access to the questions that are necessary for practice and reinforcing the concepts of the chapter. 

• You can use the pdf at your own pace, re-visiting the specific section or problems as you need. This flexibility helps you to prepare for tests and exams. 

• If you have any doubts or problems while solving the problems, the solutions can help you overcome them.

• You can improve your performance in exams by using the solutions. NCERT Solutions are aligned with your curriculum and exam patterns, so you are well prepared for assessments. 

• The solutions not only give answers but also explain the concepts behind them. This helps you to understand the subject better, so you can apply the concepts in real-world situations.

Frequently Asked Questions

Question 1: How is sound produced and detected?

Answer 1: In this chapter, we look at how sound is created by vibrations, and how those vibrations are picked up by the human ear, or by electronic devices such as microphones. We also look at how different musical instruments create sound.

Question 2: What is the significance of the study of echoes and reflection of sound?

Answer 2: echoes and sound reflection can be used for a variety of purposes, including acoustic design, distance measurement, and understanding how sound waves interact with surfaces.