NCERT Solutions for Class 9 Science Chapter 12 – Sound

NCERT Class 9 Science Solutions for Chapter 12 ‘Sound’ will help you prepare the best for CBSE exams. NCERT Solutions for Chapter 12 deals with concepts like amplitude, frequency, vibrations, mechanics behind SONAR and the velocity of sound. There are a total of 10 exercises and 38 questions in the chapter.

This chapter includes a variety of exercises such as diagram based questions, questions which require comparative analysis, numerical and experimental questions. These questions will put your analytical and observation skills to action. Concepts like the mechanics of SONAR, wavelength and mechanical waves require a good deal of understanding and application skills. Overall the chapter has a lot to offer in terms of fundamentals of sound.

NCERT solutions for class 9 science chapter 12 will help you prepare all these topics thoroughly so that you can score better marks in your exams. Before you start solving the NCERT exercises for chapter 12, take a quick look at the important topics of the chapter. This summary will help you revise the chapter and hence you will be able to solve the questions easily.

Important Topics for NCERT Class 9 Solutions for Chapter 12: Sound

As the name suggests, the NCERT Solutions Class 9 Science Chapter 12 – Sound elaborates the concept of sound along with the terms related to it. Sound is defined as the disturbances which reach our ears. Sound is produced by vibrations.

 Whenever a body vibrates, it forces the particles present in its neighbouring medium to vibrate. This leads to the creation of disturbance in a medium and on travelling it gives rise to waves. These waves or disturbances reach our ears and we call them sounds.

 A sound wave is also termed as a longitudinal wave. This is because the particles of the medium producing the sound travel in a direction parallel to the direction of the propagation of disturbance. 

Sound also tends to follow all the laws of reflection as they are followed by light. The waves of sound which are incident and then reflected, form the exact same angle with the normal to the surface the point of incidence, as the light rays. Moreover, like the light waves, the incident sound wave and the reflected sound wave and the normal to the point of reflection, all lie in the same plane. 


Wavelength is defined as the distance between the two consecutive compressions or the distance between the two consecutive rarefactions. The SI Unit of wavelength is Meter(m).


The total number of complete oscillations occurring per second is termed as the frequency of that sound wave. It is measured in Hertz (Hz). 


Amplitude is explained as the maximum height that is reached by the crest or the through of a sound wave. 

Longitudinal waves 

When the vibrations of a medium journey in a parallel direction to the direction of the wave, they are termed as longitudinal waves. A sound wave is also a longitudinal wave. 

Numerical problems 

The chapter has many numerical problems which require you to find the speed of sound, its velocity, its wavelength, amplitude etc. 

Example –

A sound wave travels at a speed of 339 m/s. if its wavelength is 1.5 cm, what is the frequency of the wave and will it be audible?

Solution –

Speed of sound (given), v = 339 m/s

Wavelength of sound (given), ƴ = 1.5 cm = 0.015 m

Speed of sound = wavelength x frequency

Therefore v = 339/0.015 = 22600 Hz 

Answer – the frequency of audible sound lies between 20 Hz to 20,000 Hz. Since the frequency of the sound here is 22600 Hz which is more than the range mentioned, it will not be audible. 

Exercise-wise Discussion of NCERT Class 9 Solutions Chapter 12 – Sound

  1. The first exercise of NCERT Class 9 Solutions for Chapter 12 begins with theory-based questions whose answers are derived directly from the concepts of the chapter. 
  2. There are questions which ask you to explain how sound is produced from a vibrating body, why are sound waves called mechanical waves etc. 
  3. Also, there are definition-based questions like those which ask you to write what amplitude means, or the definition of frequency, wavelength, time period, amplitude etc. 
  4. Further, there are questions which require comparative analysis, like a question which requires you to differentiate between the loudness of a sound and the intensity of a sound. 
  5. There are questions which require you to pen down an experiment. Many questions are derived from real-life conditions. 
  6. There are numerical problems in the chapter which require you to find terms like the wavelength, frequency, velocity of sound etc. 

About NCERT Solutions for Class 9 Science Chapter 12 by Instasolv

  • We have adhered to the latest CBSE syllabus while formulating the NCERT solutions for class 9 science chapter 12. 
  • We make sure that along with the correct solutions you achieve a strong understanding of the concepts as well. 
  • The answers are given in a step by step format, to ensure that all your doubts are solved. 
  • All the questions have been carefully tackled and no stone has been left unturned. 

At instasolv we are devoted to quality learning and productive outcomes. With our help and guidance, we ensure that you get well accustomed to the chapter and all its fundamental concepts. Once you invest your time in the Instasolv’s NCERT Class 9 Science Solutions for Chapter 12 – Sound, you will get strong command on all its ideas and basics. With us, holding your back, no hurdle can come in your way and nothing can stop you from scoring high in your exams.