Samacheer Kalvi 8th Science Solutions Chapter 6 Pdf

Samacheer Kalvi 8th Science Solutions Chapter 6 Pdf

Tamilnadu Board Samacheer Kalvi 8th Science Solutions Chapter 6: Tamilnadu State Board Solution Class 8 Science Chapter 6 – Sound.

Samacheer Kalvi 8th Science Solutions Chapter 6: Overview

Board

Samacheer Kalvi
Class

8

Subject

Science
Chapter

6

Chapter Name

Sound


Samacheer Kalvi 8th Science Solutions Chapter 6 Pdf

(I) Choose the best answer.

(1 ) Sound waves travel very fast in

a ) air

b) metals

c) vacuum

d) liquids

(2) Which of the following are the characteristics of vibrations?

i ) Frequency

ii ) Time period

iii ) Pitch

iv) Loudness

a) i and ii

b) ii and iii

c ) iii and iv

d) i and iv

(3) The amplitude of the sound wave decides its

a) speed

b) pitch

c) loudness

d) frequency

(4) What kind of musical instrument is a sitar?

a ) String instrument

b) Percussion instrument

c) Wind instrument

d) None of these

(5) Find the odd one out .

a) Harmonium

b) Flute

c) Nadaswaram

d) Violin

 

(6) Noise is produced by

a) vibrations with high frequency.

b) regular vibrations.

c) regular and periodic vibrations.

d) irregular and non- periodic vibrations.

(7 ) The range of audible frequency for the human ear is

a) 2 Hz to 2000 Hz

b) 20 Hz to 2000 Hz

c) 20 Hz to 20000Hz

d) 200 Hz to 20000 Hz

(8) If the amplitude and frequency of a sound waves are increased ,which of the following is true?

a) Loudness increases and pitch is higher.

b) Loudness increases and pitch is unchanged.

c) Loudness increases and pitch is lower.

d) Loudness decreases and pitch is lower.

 

9) Which of the following may be caused by noise?

a) Irritation

b) Stress

c) Nervousness

d) All the above

 

(II). Fill in  the blanks .

1 ) Sound is produced by vibrating bodies.

2 ) The vibrations of a simple pendulum are also known as oscillation.

3) Sound travels in the form of waves.

4) High frequency sounds that cannot be heard by you are called Ultrasonic.

5) Pitch of a sound depends on the frequency of vibration.

6) If the thickness of a vibrating string is increased, its pitch will be decreased .

(III) Match the following.

Ultrasonics Frequency below 20 Hz
Speed of sound in air Needs material medium
Infrasonics 330 ms-1
Sound propagation Frequency more than 20000 Hz

Answer

Ultrasonics Frequency more than 20000 Hz
Speed of sound in air 330 ms -1
Infrasonics Frequency below 20 Hz
Sound propagation Needs material medium

(IV) Consider the statements given below and choose the correct option.

1 ) Assertion : When lightning strikes, the sound is heard a little after the flash is seen.

Reason : The velocity of the light is greater than that of the sound.

Answer : A . Both assertion and reason are true and reason is the correct explanation of assertion.

2 ) Assertion : Two persons on the surface of the moon cannot talk to each other.

Reason : There is no atmosphere on moon.

Answer : A . Both assertion and reason are true and reason is the correct explanation of assertion.

(V) Answer briefly.

1 ) What is vibration?

When an object is set to vibrate, then there is formation of sound. A kind of rapid back and forth motion of a particle is known as vibration.This back and forth motion of the particles enables the substances around it to vibrate .This results in the spreading of sound to the surroundings.Medium refers to the substance through which there is transmission of sound. It  is the medium, which permits the sound to travel from the point of generation to the listener.

2) Give an example to show that light travels faster than  sound?

Lightning is one of the most common example which depicts that light travels faster than sound.We always perceive the lightning first, whenever there is a lightning strike and then the sound of the thunder is heard after some period of time.

This is one of the most relevant example that clearly manifests that light travels faster than sound.

3) To increase loudness of sound by four times, how much should the amplitude of vibration be changed ?

As we know that ,loudness of a sound is dependent on the amplitude of the vibration. For this reason, it is necessary to increase the amplitude of the vibration by fourtimes, in order to increase loudness of sound by four times.

4 ) What is an ultrasonic sound?

Ultrasonic sound refers to a sound, whose frequency is higher than 20000 Hz . Bats, dogs and dolphins are for instance ,those animals who possesses the ability to hear certain ultrasonic sounds.

The uses of ultrasonic sounds are as follows :

  • Sonogram is a medical applications ,where it is used to a great extent .
  • It is used in the SONAR system for the purpose of detecting the depth of the sea and the enemy submarines.
  • It is also used in dishwashers.

5) Give two differences between music and noise.

Music

1 ) The regular patterns of vibrations give rise to the formation of music.

2 ) The sound that is produced by music is not harsh to the human ear  but rather it gives a pleasing sensation to the ear.

Noise

1 ) The irregular and non- periodic vibrations leads to the formation of noise.

2) The sound that is produced by noise does not provide a pleasing sensation but rather it gives an unpleasant sound which is disruptive to the ear.

6) What are the hazards of noise pollution?

The hazards of noise pollution are as follows :

  • Noise may give rise to headache, stress irritation and nervousness.
  • The sleeping pattern of a person may change, if that person is exposed to noise for quite a long period of time.
  • Constant exposure to noise may bring about a negative impact on the hearing ability.
  • Instant exposure to loud noise may lead to heart attack and loss of consciousness.
  • Continuous exposure to noise might divert the concentration of a person from his or her assigned task.
  • A person’s peace of mind is greatly affected by noise pollution. Itextends the current tension of modern day living.

7 ) Mention few measures to be taken to reduce the effect of noise pollution.

By adopting the following steps, noise pollution can be reduced to a considerable extent.

  • Strict guidelines should be regulated for the proper usages of loudspeakers on various religious, social and political events.
  • There should be an effective silencers on every automobiles.
  • While driving, people should be encouraged to abstain from enormous honking.
  • There should be a proper maintenance of industrial machines and home appliances
  • There must be operations of all communication system on a moderate volume
  • Residential areas should get rid of heavy vehicles

8) Define the following terms.

a.) Amplitude  b) Loudness

a) Amplitude

The greatest displacement of a vibrating particle from its mean position is known as amplitude. It is indicated by ‘A’ . The unit of amplitude is represented as ‘metre’ (m).

b.) Loudness

The feature of a sound that permits us to differentiate a fragile or weak sound from an intense or loud sound is known as loudness. The loudness of sound is dependent on its amplitude. On one hand, the sound will be louder, if the amplitude is higher and on the other hand, the sound will not be louder, if the amplitude is lower. There is formation of a weak sound when a drum is beaten softly. But, there is formation of a loud sound, when a drum is beaten strongly. The unit of loudness of sound is represented as decibel (dB).

9) How does planting trees help in reducing noise pollution?

Stems , leaves , branches and wood are for instance, the parts of plant which helps in absorbing the sound. The thick fleshy leaves and rough barks performs an effective role in absorbing sound because of their dynamic surface area and aids in lowering noise pollution. So, this way, planting trees can be quite effective in decreasing noise pollution.

(VI) Answer in detail.

1 ) Describe an experiment to show that sound cannot travel through vacuum.

Method

Firstly, a bell jar and mobile phone should be taken. Then, the mobile phone should be placed inside the jar by switching on the music. Now, the air from the jar should be pumped out with the help of a vacuum pump. The sound from the mobile phone becomes weak and ultimately it becomes extremely feeble, when there is more and more air removal from the jar.

Inferences

From this experiment we can clearly depict that, sound always requires a medium for propagation as for example ,air  and it could not travel in vacuum. Sound can travel both in water as well as in solids. The speed of sound is greater in solids when compared to liquids and it is extremely minimal in gases.

2) What are the properties of sound?

Not all sounds that we hear are of the same type. On the basis of some properties, one kind of sound can be distinguished from another kind of sound. The properties of sound are :

  • Loudness
  • Pitch
  • Quality or Timbre

Explanation :

Loudness 

The feature of a sound that permits us to differentiate a fragile or weak sound from an intense or loud sound is known as loudness. The loudness of sound is dependent on its amplitude. On one hand, the sound will be louder, if the amplitude is higher and on the other hand, the sound will not be louder, if the amplitude is lower. There is formation of a weak sound when a drum is beaten softly. But, there is formation of a loud sound, when a drum is beaten strongly. The unit of loudness of sound is represented as decibel (dB).

Pitch

The feature of sound that permits us to differentiate between a flat sound and a shrill sound is known as the pitch. The pitch will be quite higher, if the frequency of sound is higher. The shrillness to a sound are  added by high pitch. The sound that are formed by a whistle , a flute and a violin falls under the category of high pitch sounds. Female’s voice has a greater pitch  when compared to a male’s voice. For this reason, there is more shrillness  in a female’s voice in comparison to a male’s voice. Roaring of a lion and beating of a drum are some of the perfect examples of low pitch sound.

Quality or Timbre

The feature of sound that facilitates us to differentiate between two sounds having a similar peach and amplitude is known as the quality or timbre. In an orchestra, the formation of sounds by some musical instruments having similar peach and loudness is one such example.

3) What steps should be taken to reduce the effect of noise pollution?

By adopting the following steps, noise pollution can be reduced to a considerable extent.

  • Strict guidelines should be regulated for the proper usages of loudspeakers on various religious, social and political events.
  • There should be an effective silencers on every automobiles.
  • While driving, people should be encouraged to abstain from enormous honking.
  • There should be a proper maintenance of industrial machines and home appliances
  • There must be operations of all communication system on a moderate volume
  • Residential areas should get rid of heavy vehicles
  • According to the regulations of the pollution control board, green corridor belt should be established around the industries.
  • People who are working in noisy factories should be encouraged to wear ear plugs because it will reduce the risk of hearing loss.
  • People should use curtains and cushions in their home, as it acts as an absorbing material and they should also be motivated to plant trees.

4) Describe the structure and function of the human ear?

Ear is an essential organ which enables all animals to hear a sound. Human ear possesses the capacity to pick up and interpret high frequency vibrations of air. Pinna refers to the external and visible part of the human ear. It is mainly designed for the purpose of gathering sound from the environment,  which then reaches the eardrum with the help of the ear canal. When the drum are striked by the sound wave, then the ossicles moves inside and outside in order to generate the vibrations. Then there is a special kind of cells in the inner ear which picks up these vibrations. In the form of signals the vibrations are sent to the brain from the inner ear. These signals are perceived as sounds by the brain .

(VII) Problems .

1 ) Ruthvik and Ruha hear a gunshot 2 second after it is fired. How far away from the gun they are standing? (Speed of sound in air is equal to 330 ms –1 )

The data which are already given :

time (t) = 2 s

Speed of Sound (V) is equivalent to 330 ms -1

Now, we have to find the Distance (d)

Formula :

Distance = speed × time

= 330 × 2 = 660 m

So, they are standing 660 m away from the gun .

2) A sound wave travels 2000 m in 8 s . What is the velocity of the sound ?

The data which are already given :

Distance that a sound wave(d) travelsis equivalent to 2000 m .

time taken to travel the given distance = 8 s

Now, we have to find the velocity of the sound (V) Formula :

Velocity (V) = distance (d)/ time (t)

V   = 2000m / 8s

 

Samacheer Kalvi 8th Science Solutions Chapter 6 Sound Tamilnadu Board Class 8 Samacheer Kalvi Science Chapter 6

= 250 m/s

So, the velocity of the sound is 250 m/s .

 

3) A wave with a frequency of 500 Hz is traveling at a speed of 200 ms –1. What is the wavelength?

The data which are already given:

Frequency (n) is equivalent to 500 Hz

Speed (V) = 200 ms -1

Now, we have to find the wavelength (`^ )

Formula :

Wavelength (`^) = Velocity (V) / Frequency (n)

`^ = 200/ 500

= 0.4 m

Therefore, the wavelength is 0.4 m .

Updated: November 22, 2021 — 4:14 pm

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