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Kerala State Syllabus 8th Standard Basic Science Solutions Chapter 19 Sound
Sound is a form of energy which is familiar to us and necessary for communication. Three components are essential to experience the sound. Source of sound, medium, and the ear.
Source of sound
The sources that produce sound is called sources of sound. We can classify the sources of sound into two. Natural sources of sound and manmade sources of sound. Sound is produced by the vibration of object. The object that produces sound is called the source of sound.
Hss Live Guru 8th Physics Kerala Syllabus Natural frequency
When a body is set into vibration it vibrates with particular frequency of its own. This frequency is called its natural frequency. The unit of frequency is hertz (Hz). The constituents those affect the natural frequency of an object are the nature of the object, length of the object, surface area, tension of the object, etc.
Frequency (f) = Number of vibration(n)/ time(f)
Pitch and loudness
The sharpness of the sound heard is called the pitch. It depends on its frequency of sound. Cuckoo’s cry, female voice etc have high pitch and male voice, duck’s sound, lion’s roar, etc have low pitch. Loudness is the measure of audibility of a person. This depends mainly on frequency of sound and the sensory ability of the ear. Its unit is decibel (dB).
Kerala Syllabus 8th Standard Physics Notes Propagation of sound
A medium is necessary for sound to propagate. Sound is propagated not only through air but also through other substances. Loss of hearing is a disability of the ear. The people having damage to ear by birth effect many difficulties for commu¬nication, for ability to speak, vulnerability to danger, etc.
Class 8 Physics Notes Kerala Syllabus Limit of audibility
We cannot here sound of all frequencies. We can hear the sound of frequency in between 20 Hz and 20000Hz. Sounds with frequency less than 20 Hz are called infrasonic and that greater than 20000Hz are called ultrasonic. Ultrasonic sounds are used in the instrument sonar and in medical field.
Hss Live Guru 8th Basic Science Kerala Syllabus Noise pollution
Kerala is one of the places which is highest noise pollution in the world. Noise effects not only ear but mental, emotional level, and physical problems. Reduce the use of air horns, use silencers in vehicles, planting trees, etc are some ways to reduce noise pollution.
Sound Textbook Questions & Answers
Hsslive Guru Physics 8th Standard Kerala Syllabus Question 1.
If a tuning fork vibrates 480 times in one second, what would be its natural frequency?
Answer:
Natural frequency = 480Hz
Kerala Syllabus 8th Standard Chemistry Notes Question 2.
If a simple pendulum oscillates 10 times in 10 seconds, what would be its frequency?
Answer:
n = 10
t = -10 s
\(\mathrm{f}=\frac{n}{t}=\frac{10}{10 s}=1 \mathrm{Hz}\)
Hsslive Guru 8th Class Physics Kerala Syllabus Question 3.
What are the factors influencing the natural frequency of a body?
Answer:
i. Nature of the object
ii. Length
iii. Tention
iv. Surface area
v. Area of cross-section
Hss Live Physics Class 8 Kerala Syllabus Question 4.
The frequencies of certain tuning forks are given below. Find out which among these have the highest and the smallest pitches.
(256 Hz, 512 Hz, 480 Hz, 288 Hz)
Answer:
High pitch = 512 Hz
Low pitch = 256 Hz
Kerala Syllabus 8th Standard Basic Science Notes Question 5.
In the sources of sound given below, vibration in which main part produces sound?
a. Chenda
b. Flute
c. Vocal cord
Answer:
a. Chenda – Diaphragm
b. Flute-Air
c. Vocal box – vocal cord
Kerala Syllabus 8th Standard Chemistry Notes Malayalam Medium Question 6.
Design an activity to prove that sound can he propagated even through solid substances.
Answer:
Answer:
Press the ear on one end of a iron rod and beat on the other end with another iron rod or, toy telephone
8th Standard Physics Notes Kerala Syllabus Question 7.
Say whether the following statements given below are true or false.
If false, rewrite it by making necessary changes.
a. Sound cannot travel through vacuum.
b. When frequency of sound increases, pitch decreases.
Answer:
a. correct
b. false, when frequency decreases pitch decreases
Kerala Syllabus 8th Standard Physics Question 8.
‘Bats can catch prey even in the dark’. Do you agree with this statement? Explain your inference.
Answer:
Agree. Bats can produce and hear ultrasonic waves. The sound they produced reflects by hitting on objects. The bats can analyze the returning sounds.
8th Class Biology Notes Pdf Kerala Syllabus Question 9.
How do human beings contribute to noise pollution?
Answer:
- Air horn
- Loudspeaker
- The sounds of vehicles etc
8th Standard Chemistry Notes Pdf Kerala Syllabus Question 10.
Which unit represents loudness? (Hz, m/s, dB, W)
Answer:
dB
Sound Additional Questions & Answers
8th Standard Chemistry Notes Kerala Syllabus Question 1.
Complete the table
| Source of sound | The main part which produces sound by vibration | The part which vibrates with the main part |
| Voicebox | ….. a …….. | Throat, lips |
| Flute | Air column | …. b ….. |
| Chenda | Leather, diaphragm | …… c ……. |
| Violine | ……… d ………. | Frame, air |
Answer:
| Source of sound | The main part which produces sound by vibration | The part which vibrates with the main part |
| Voicebox | Vocal cord | Throat, lips |
| flute | Air column | Throat, air |
| chenda | Leather, diaphragm | wooden frame, cord |
| Violine | Metal Wire | Frame air |
Basic Science Class 8 Sound Kerala Syllabus Question 2.
Fill suitably
Frequency – hertz; Loudness- ………….
Answer:
decibel (dB)
Class 8 Science Notes Kerala Syllabus Question 3.
Table the following as those having high pitch and low pitch separately.
Cuckoo’s cry, lion’s roar, female voice, duck’s sound, male voice, air horn
Answer:
| high pitch | low pitch |
| Cuckoo’s cry | Lion’s roar |
| Female voice | Duck’s sound |
| Air horn | Male voice |
Class 8 Physics Kerala Syllabus Question 4.
Table the natural source and manmade source from the following. Lips, chenda, flute, tabla, violin, vocal cord, sound of birds
Answer:
| Natural | Man-made |
| Lips | Chenda |
| Vocal cord | Flute |
| Sound of bird | Tabala |
| Violin |
Vibration Solutions Question 5.
What is the relation between the length of the pendulum and frequency?
Answer:
When the length of the pendulum increases, the frequency decreases.
Question 6.
Will the intensity of sound increase when the instrument like chenda and maddalam are beaten strongly? Justify your answer.
Answer:
Yes. When beaten strongly the diagram vibrates with greater amplitude and increases frequency and loudness
Question 7.
What are the demerits of sound pollution?
Answer:
- Causes mental stress.
- Causes emotional strain
- Causes deafness
- Increase the blood pressure
Question 8.
Write the ways to reduce sound pollution.
Answer:
- Ban the air horn
- Control loudspeakers
- Use silencers in vehicles
- Control the sound having more than 50 dB near the hospitals
Question 9.
Write two uses of ultrasonic sound.
Answer:
Use in SONAR
To find out the disease and treatment in medical field
Question 10.
Can we hear the sound from Galton whistle having a frequency of 30000Hz? Why?
Answer:
No. We cannot hear the sound having a frequency greater than 20000Hz
Question 11.
What are the problem faced by deaf people?
Answer:
The people having damage to hereby birth effect many difficulties for com¬munication, for ability to speak, vulnerability to danger, etc.
Question 12.
Complete the table.
| No of vibrations | time | Frequency |
| 10 | ….. a …. | 2 |
| 15 | 3 | …… b ….. |
| ……. c ….. | 5 | 4 |
Answer:
a. 5
b. 5
c. 20
Question 13.
An object vibrates 200 times in one second. What is its frequency?
Answer:
frequency = \(\frac{n}{t}=\frac{200}{1}=200 \mathrm{Hz}\)
Question 14.
How many times vibrate a body of frequency 290 Hz in 12 seconds.
Answer:
n = f × t
f = 290 Hz,
t = 12 s
n = 290 × 12 = 3480 times
Question 15.
Name the sounds of frequency below 20 Hz and above 20000 Hz.
Answer:
below 20 Hz = Infrasonic
Above 20000 Hz = ultrasonic