Sound Class 8th Science

 NOTES PREPARED BY 

ASHAQ HUSSAIN BHAT 

TEACHER SCHOOL 

EDUCATION DEPARTMENT 

JAMMU AND KASHMIR

''SOUND"

Additional Question's

Q1. What is a wave?

Ans: A wave is a vibratory disturbance in a medium which carries energy from one point to another point without there being a direct contact between two points.  A wave is produced by the vibration of particles of medium through which it passes. When a wave passes through a medium, the medium itself doesnot move along the direction of the wave only the particles of medium vibrate about their fixed position.

Q2. Define sound ?
Ans: Sound is a form of energy which gives us sensation of hearing. Sound can be also defined as the vibration in a medium which travels as an audible mechanical wave of pressure and density grandient

Q3. What is longitudinal wave?

Ans: A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. E.g, a wave which travels along a spring when it is pushed or pulled at one end is longitudinal wave. Sound waves also travel in the form of longitudinal waves.

Q4. What is compression and rarefraction of a longitudinal wave?

Ans: Compression: A compression is that part of longitudinal wave in which the particles of medium are closer to one another than they normally are and there is a momentry reduction in volume of medium

Rarefraction : A rarefraction is that part of a longitudinal wave in which the particles of a medium are farther apart than normal and there is momentary increase in ther volume of medium

Q5. What are transverse waves?

Ans: A wave in which the particles of medium vibrate up and down at right angles to the direction of propagation of wave is known as transverse wave. eg. the water waves formed on the surface of water in a pond are transverse waves. Light also travels as a transverse wave.

Q6. Define crest and trough of a transverse wave?

Ans :- 1) Crest:  The elevation or humo in a transverse wave is called crest. In other words a crest is that part of a transverse wave which is above the line of disturbance of the medium
2). Trough: The depression or hollow in a transverse wave is called trough. So, a trough is that part of a transverse wave which is below the the line of  (Zero) disturbance of the the medium

Q . 7:- Define Time period, Frequency and Velocity

1) . Time period: The time period required to produce one complete wave is called the time
period of the wave. The S I unit of the time period of the wave is second.
2). Frequency: The Number of complete waves produced in one second is called frequency
Frequncy tells us the rate at which the waves are produced by the source.
3). Velocity: The distance travelled by the wave in one second is called velocity of the wave. The SI unit for measuring the velocity of the wave is m/sec.

Q8. What are the charecteristics of sound ? 

Ans:  A sound wave can be completely described by five characteristics. These are as follows:
i). Wave length: The minimum distance in which a sound wave repeats itself is called wave length or the distance between the two consecutive crusts or troughs is known as wave length. The  wave length is denoted by a Greek letter 入 (lambda). The SI unit of wave length is metres.
ii). Amplitude: The maximum displacement of the particles of the medium from there
original position when a wave passes through the medium is called Amplitude of the wave.
The Amplitude of the wave is same as the amplitude of vibrating body producing the
wave. The S.I unit for  amplitude is metre.
iii). Time period: The time required to produce one complete wave is called the time period of
the wave. The SI unit of the time period of the wave is second.
iv). Frequency: The Number of complete waves produced in one second is called frequency.
Frequency tells us the rate at which the waves are produced by their source.
v). Velocity : The distance travelled by the wave in one second is called velocity of the wave. The SI unit for measuring the velocity of the wave is m/sec.

Q 9. What are the charecteristics of sound?

Ans: The sound has three main charecteristics. These are as follows:

i). Loudness: Loudness of a sound is a measure of sound energy reaching the ear per second. Loudness of a sound depends on ther amplitude of sound wave. Greater the amplitude of sound wave louder will be the sound. The loudness of the sound is measured in decibles(db).

ii). Pitch : That characteristics of sound by which we can differentiate between the sounds of same loudness. Pitch of the sound depends up on frequency of vibrations. Faster the vibration of the sound producing source, higher is the frequency and higher is the pitch.

iii). Quality: (Timbre) is the characteristics of sound which enables us to distinguish between the sounds of same loudness and same pitch produced by different musical instruments or different singers. The quality of a sound depends upon the shape of the sound wave produced by the source.

Q10 . Give the working and construction of Ear?

Ans: The Ear is the organ that detects sound . It not only receives sound but also aids in balance and body position. The ear is a part of our auditory system.

Construction: The ear consists of three parts, Outer ear, Middle ear, and Inner ear.

The outer ear is the most external portion of the ear. The outer ear is the only visible portion
of ear in humans and almost in all vertebrates. The outer ear is called Pinna or Auricle in
human beings. The Pinna is connected to two to three cm long passage called ear canal. At
the end of ear canal is a thin elastic membrane called tympanium or ear drum.

The middle ear contains three small and declicate bones called hammer, Anvil and Strup. These bones are linked to one another. One end of hammer is connected to ear drum the other is connected to Anvil. The lower end of middle ear has a narrow tube called Eustachian tube going to throat.

The inner ear has a coiled tube called Cochlea. One side of Cochlea is connected to the middle ear through the elastic membrane over the oval window. The cochlea is filled with liquid which contains nerve cells sensitive to sound. The outer side of cochlea is connected to auditory nerve which goes to the brain.

Working of ear: 

The sound waves coming from the source are collected by pinna of external ear. These sound waves pass through the ear canal and fall on ear drum, which starts vibrating back and forth rapidly. The vibrating ear drum passes these vibrations to hammer. From hammer vibrations pass to anvil and strrup, which passes these vibrations to the oval window from oval window vibrations pass on to liquid in cochlea, which then starts to vibrate. Vibrating liquid of cochlea sets elelectrical impulses in the nerve cells present in it. These electrical impulses are carried by auditory nerve to the brain. The brain interprets these electrical impulses as sound and we get the sensation of hearing.

Q. Give the relationship between frequency and time period?

Ans: We know time period = 1/No. of waves per sec.

But we know No. of waves / sec. = frequency (V)

Therefore T = 1V

Thus time period is inversely proportional to frequency.

Q. What is the function of three tiny bones in the middle ear?

Ans: The function of three tiny bones in the middle ear is to increase the strength of vibration coming from ear drum before passing them onto the inner ear. These three bones amplify the sound vibrations upto 30 times.

Q. Give the relationship between velocity, wavelength, frequency.

Ans: Velocity of wave = Frequcency × Wave length

                           v=V x

Speed/velocity   = Distancetravelled/Time takeri

                            V = λ/T

                            V=  λ ×1/T     (1/T= Frequency = V)

                            V= λ × V

                                     

Taxtual questin:

Q5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency?

Sol: No. of oscillations in 4 seconds = 40

No. of oscillations 1 second = 40/4

= 40 /sec.

But we know No. of oscillations per second is known as frequency

Therefore V = 10hz.

We know T = 1/v

=T= 1/10

= T = 0.1 sec.

 Hence

V = 10hz.

T = 0.1sec

Q. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Sol. No. of oscillations per second is known as frequency

V = 500hz.

T = 1/V

= T = 1/500

Therefore T= 0.002 seconds

Q. Identify the part which vibrates to produce sound in the following instrumemnts.

a). Dholak

b). Sitar 

c). Flute

Ans: Membrane of Dholak vibrates to produce sound. 

Strings of sitar vibrates to produce sound.

Air column inside the flute vibrates to produce sound.

Q What is the diffierence between noise snd music? Can music become noise sometimes?

Ans: The arrangement of sounds of different frequencies called notes in a way ,that it is

pleasent to our ears is known as music. On the other hand the sound which is unpleasant to

our ears is called noise. 

Yes, music can become noise sometimes if musical sound is too loud then it becomes noise.

Q. List sources of noise pollution in your surroundings?

Ans: The presence of unwanted and disturbing sound in our environment is called noise

pollution. The major sources of noise pollution in our environment are:

a). The motor vehicles running on the road produce noise pollution by blowing horns and

sounds of their engines also leads to noise pollution

b). Bursting of crackers on various social and religious occasions produces noise pollution

c). The various machines in factories produces noise pollution

d). Playing of loud speakers and bands causes noise pollution.

e). Different kitchen appliences like grinders, mixers etc. also produce noise pollution.

Q. Explain in what way noise pollution is harmful to humans?

Ans: Noise pollution is harmful to humans in many ways. It causes many health related problems. The various harms of noise pollution are as under

i). Loud noise can cause partial or permanent hearing loss.

ii). Loud noise can cause irritation and headache.

IiI). Loud noise can cause ailment called hypertention that is high blood pressure.

iv). Loud noise can cause a person to lose concentration in his studies and work.

v). Loud noise can cause insomia that is inability to sleep.

Q. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer?

Ans: We will suggest our parents to buy the house which is three lanes away from busy road. This is because being away from the busy road will reduce noise pollution caused by heavy traffic on the road. As the intensity of sound decreases with increase in distance between source and listener. This will make us to live comfortably in the house.

Q. Lightening and thunder take place in the sky at the same time and at the same distance from us. Lightening is seen earlier and thunder is heard later. Can you explain?

Ans: Lightening and thunder takes place at the same time and at the same distance from us but we see lightening earlier than we hear thunder. Because light travels faster than sound. The speed of light in air is 340m/sec. That is why we see lightening earlier than we hear thunder.

Q. Sketch larynx and explain its functions in your own words.

Ans: Larynx is a part of the throat. It is responsible for production of sound. A sketch of human larynx is shown in fig. 

Larynx moves when we swallow something. Inside the larynx there are  two vocal cords. There is a small gap between them. This gap allows air to pass through. When we speak air is  forced into this small gap by the lungs. This prompts vocal cards to vibrate. Since vibrating objects produce sound it is because of vibration of voacal cords sound is produced.

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