CBSE Class 8 Science Sound Chapter Notes

Scroll down for PDF

CBSE Class 8 Science Sound Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

SOUND

Sound is a form of energy which produces the sensation of hearing in our ear's.

HOW SOUND IS PRODUCED
The following activities will help you understand how sound is produced.

ACTIVITY
Place a metallic/plastic ruler on the table. Take care to place it in such a way that 2/3rds of the scale projects (just out) from the edge of the table. Place a heavy object such as a dictionary or a brick on the ruler. Now press the projecting end downwards and release it abruptly. What do you observe?


class_8_science_concept_045

You wil see that the ruler snaps back and starts vibrating. At the same time, it also produces a sound. Once the vibrations stop, the sound also stops.
Vibrating Bodies Produce Sound

Cut a rubber band. Hold one end of it in your mouth and the other end in your hand and stretch it. Now, pull it with the other hand and release it (fig). What happens to the rubber band? You will notice that it moves to and fro or vibrates and it also produces sound.

class_8_science_concept_046

Sound from a Vibrating Blade
Take a used shaving blade and fix it on a table, or desk as shown in Fig. Bend the upper end of the blade and leave it. The blade begins to vibrate. You can actually see it vibrating. Touch the blade carefully with your finger. It stops vibrating. Does it produce any sound now?

Conclusion : From these activities, we come to the conclusion that the sound is produced by the vibrating objects or bodies.

Characteristic of Vibrations : In sound producing objects, the vibrations take place very fast...so fast, in fact, that they cannot be seen very clearly with the unaided human eye (slow-motion video is one practical solution that is routinely used in scientific and industrial applications). We can produce slower vibrations, which are also called oscillations, by an arangement called a simple pendulum. It consists of a ball or any weight, such as a stone, wooden top, steel bolt, etc. which is here called a bob, and which hangs down vertically.

class_8_science_concept_047

Figures show a oscillating simple pendulum and a vibrating string depicting the mean position and amplitude. by means of a thread. It hangs vertically because of the force of gravity acting upon it. When the bob is given a small push, it performs a to-and-fro motion for some time and ultimately stops. The position where the bob stops is called the mean position (A) or the equilibrium position.

class_8_science_concept_048

AMPLITUDE
The maximum displacement of the bob from the mean position during oscilations is called amplitude of the oscillation. In the case of a simple pendulum, as show in the figure, the amplitude is AB (or AC).

FREQUENCY
The number of oscillations produced by the vibrating body in one second is called its frequency. It is denoted by the letter 'f'. The unit of frequency in SI
system is Hertz (Hz or s–1). When a vibrating body produces 10 vibrations (oscillations) in one second, its frequency is said to be 10 hertz.
If the frequency of a tuning fork is written as 200 Hz, it means that it produces 200 vibrations in one second.

TIME PERIOD
When a bob moves from one position and returns to the same position, such that it repeats the motion, it is said to complete on oscillation.

The time taken by a vibrating body to complete one oscilation is called the time period.

class_8_science_concept_049

TRY YOUR SELF
Q. Define vibrations Q. How is sound produced?
Q. What is meant by oscillatory motion? Q. Define frequency.
Q. Give the unit in which frequency is measured.
Q. The sound from a housefly is produced when it vibrates its wings at an average rate of 300 vibrations per second. What is the time period of the vibration?
Q. The frequency of a given sound is 4.5 kHz. how many vibrations is it completing in one second?

Please click the link below to download pdf file for CBSE Class 8 Science Sound Chapter Notes.


Click on the text For more study material for Science please click here - Science

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

CBSE to conduct a voluntary test for class 11th and 12th

Nowadays students have the liberty to choose the field they seem to fit in. A few years back the problem was parents who burdened children with their own choices. On the other side, now students along with their parent's support are free to choose their field. Not any...

How to crack a competitive examination

“How I crack a competitive examination” is a frequently asked question by today’s students. Cracking a competitive exam is a challenging task. Attaining a huge amount of study and solving several complex problems in a limited amount of time is a huge task. Competitive...

Tips for exam preparation

Students often get nervous during their exams. The reason behind this nervousness is either a lack of confidence or a lack of preparedness. To overcome these fears students are advised to do their preparation in such a way that will retain their confidence. For this...

TIPS: Study habits for success

Being a student is fairly a difficult job. Alongside maintaining your curricular as well as extra-curricular activities adds more to it. Performance in academics is one of the major concerns. Every parent now tries to get their children more indulged in studies. Need...

JEE Entrance Exam 2020 Dates Registration Admit Cards Exam Pattern

JEE Entrance exam is conducted for students who wish to pursue engineering in different subjects or categories like mechanical, CS, etc.. It is officially organized and conducted by NTA. Formerly it was organized by CBSE. It avails seats for students in IITs, NITs, and...

Error in the evaluation of answer sheets in CBSE

The education board has witnessed many events where invigilators are being suspended for allotting wrong marks to the students.  This has affected students mainly of classes X and XII in the 2019 CBSE Board Exams. The central board of secondary education has taken...

×
Studies Today