Science Chapter 13 Sound

D.

solids, liquids and gases

A.

Baby girl

time period

amplitude

hertz

noise

frequency

Given, pendulum oscillates 40 times in 4 seconds. 
That is,

Time taken = 4 seconds

Time taken by pendulum to complete 1 oscillation = $\frac{4}{40}$ = $\frac{1}{10}= 0.1 sec$ 

So, time period of Pendulum = 0.1 seconds

That is, 

Frequecy of penduum = $\frac{\mathrm{Oscillation}}{\mathrm{time}} = \frac{40}{4} = 10 Hz$

Given,

Time taken to complete 500 vibrations = 1 second

So, time taken to complete 1 vibration = $\frac{1}{500}$ = 0.002 

Hence, time period of vibration = 0.002 seconds

Stretched membrane

Strings

Air column.

Excessive or unwanted sounds are called noise. Noise is unpleasant to hear. 
E.g., Sound produced by a bunch of students speaking together in the classroom.

The sounds which are pleasing to the ears are called music. It gives a soothing effect rather than creating a chaos in mind. 
E.g., Sound produced by a harmonium sound.

Music becomes a noise when it crosses the bearable range of sound for ears.

The sources of noise pollution in our surroundings are:

1. Honking of horns,
2. Loud sounds of machines in factories,
3. Loud musics in parties and marriages,
4. Loud sound of T.V. or radio,
5. Loud sounds of domestic electronic appliances like mixer grinder etc. 

The harmful causes of noise pollution are:

(i) Noise pollution can cause temporary or permanent damage to our ears.

(ii) High blood pressure can be as a result of noise pollution.

(iii) Noise pollution can cause mental ill health in some people. 

I would suggest my parents to buy a house which is three lanes away from the roadside. It is because the house situated on the roadside will have the following disadvantages in comparison to the house three lanes away from roadside: 

(i) Lot of noise due to passing of vehicles. 

(ii) Smoke and dust produced due to traffic on road.

(iii) Sound of pressure horns at the time of traffic jams or during peak hours of the traffic. iving in a house nearby roadside would cause noise pollution.  

Though lightening and thunder take place at the same time, we see light earlier than hearing the sound because light travels faster than sound. 

Sound is producing by vibrating bodies. Sometimes, amplitude is so small that we do not hear any sound. When amplitude of vibrations is large, we hear the sound.

To and fro or back and forth motion of an object is called vibration. 

Amplitude is the maximum displacement of vibrating a body on one side.

Larynx.

The cords which are stretched across the voice box or larynx are called vocal cords.
Two vocal cords are there across the voice box in such a way that it leaves a narrow slit between them for the passage of air. 
When the lungs force air through the slit, the vocal cords vibrate producing sound. 

No, all animals do not produce sound by vocal cords.

For example, bees buzz due to the rapid movement of their wings.    

The vocal cords in men are about 20 mm long.

15 mm.

The outer part of the ear is called pinna.

When sound enters the outer part of the ear, it travels down a canal at the end of which a thin membrane is stretched tightly. This thin and stretched membrane is called eardrum. 

The number of oscillations per second is called frequency.

The unit of frequency is hertz.

Time period is the time taken by a vibrating body to complete one oscillation. 

The loudness of sound depends on the amplitudes.

Smaller the amplitude, less is the sound and more is the amplitude of the vibrations, greater is the sound. 

The characteristics of sound which depend on frequency is called pitch of a sound.

If the frequency is high, the sound is shrill and has a higher pitch. 

Human range of human ears is 20 Hz to 20,000 Hz.

X : Ultrasonic sound,

Y : Infrasonic sound and

Z : Audible sound.

Higher is the amplitude of vibrations, louder is the voice. 

The sound having frequency more than 20,000 Hz or 20 kHz is called ultrasound. 

The loud sound which produces unpleasant sensation is called noise. 

The sound which produces pleasant sensation is called musical sound.

For example, sound produced by a harmonium is musical sound. 

Presence of excessive or unwanted gases and particles in environment is called noise pollution.

Major causes are noise from vehicles, explosions, sounds of machines, loudspeakers etc. 

Decibel (dB).

60 dB.

The disability to hear sound is hearing impairment.

The causes of hearing impairment are ear disease, injury, ageing and loud noise. 

For sound to propagate, a material medium is required. On the moon there is vacuum i.e. no air, therefore sound cannot propagate on the moon.

Hence, the astronauts cannot hear each other.

Audible range of sound is 20 Hz to 20,000 Hz. But, the frequency of vibrating pendulum does not lie in the audible range and hence, we does not hear the sound of the pendulum.

(i) Vibration: Vibration is defined as a rapid to and fro motion of a particle about a fixed position.

(ii) Time period : The time taken by a vibrating body to complete one oscillation is called its time period.

Musical instruments have strings or stretched membranes attached or fixed on them. Some instruments have slits to let air pass through them. The strings are plucked and membranes are struck to produce sound.
On plucking or striking they start vibrating, and as a result the whole instrument starts vibrating with them, which produces the music. 

When the stretched strings vibrate, they force the surrounding air to vibrate. This vibrating air, affects our eardrum and produces an audible range. 

(i) On increasing the frequency, pitch of the sound will increase.

(ii) On increasing the amplitude of vibartions, loudness of sound will increase. 

In human beings, vocal cords produce sounds. When they vibrate, they produce sound. Vocal cords are held by the muscles. The tightness with which they are determines determines the quality of sound. 

The length of the vocal cords also determines the quality of voice and is different in differnt individuals. Hence, sounds can be distinguished. 

No, we will not hear any audible sound on the surface of the moon. This is because sound requires medium to propagate, since there is no atmosphere on the surface of the moon, therefore the sound will not be heard.

Amplitude of vibration determines the loudness of a sound. 
In mosquito, the fluttering of wings produces sound. Whereas, in a lion the vocal cords produces sounds. The pitch, frequencyand quality of sound is different for both the sounds. The amplitude of sound produced by mosquito will be less than the one produced by lion.
Hence, both the sounds are distinguishable and sounds different. 

Bats produce high pitched ultrasonic waves which are not heard by human beings. The ultrasonic waves on striking the insect send back an echo, which is heard by the bat. As the echo is heard by the bat, it hover on the insect and catches it. 

Human beings cannot hear sounds below the frequency of 20 Hz and frequencies more than 20 kHz. Therefore, roughly the audible range of sounds for human beings vary between 20 Hz to 20 KHz.

Sounds with frequency above 20 KHz are called ultrasound.

Ultrasounds are not audible to human beings, but is used in a variety of field by humans. Ultrasounds are used in field of medicine to detect the disorders inside the body of human beings. They are also useful in chemical industries. They are used to detect the flaws and cracks in metallic structures. 

The unwanted and unpleasant sounds reaching our ears is noise. When the sound exceeds 80 dB, it becomes painful to bear and is called noise. They cause disturbance and is painful. 

Presence of excessive or unwanted sounds in the environment, which cause discomfort for us is called noise pollution. 

For example, excessive sounds produced by honking of horns, loud speakers, crackers, machines etc. causes noise. 

Noise pollution can be controlled by controlling those things which causes it. Some of the steps for controlling noise pollution are:

1. Blowing of honks unnecessarily should be avoided.
2. Using loudspeakers like T.V, radio should be avoided in residential areas. 
3. Trees should be planted along the roadside to create a buffer zone which will absorb excessibe sounds on the roads. 

 

(i) Frequency: Frequency is defined as the number of oscillations per second. 

(ii) Amplitude: Amplitude is defined as the maximum displacement of a particle from its rest position. 

(iii) Decibel: Decibel is the unit to measure the loudness of sound.

(iv) Music: Sound which is pleasant to ears is called music.

(v) Noise: Sound which is unpleasant to ears is called noise. 

Ill-effects of noise polution:

Noise effects has adverse effects on our body and health. It affects mental peace and health. Noise pollution is the root cause of many mental disorders like anxiety, depression etc. Apart from that physical disorders like hypertension, skin diseases, lack of sleep etc. Noise pollution affects sick people more. 

Measures to control noise pollution are:

1. Honking unnecessarily should be avoided.
2. Playing loudspeakers at residential areas should be avoided. 
3. Trees and plants should be extensively planted along the road sides to absorb sound and control noise pollution.

Vibrations of the body produce sound. The loudness of the sound depends on the amplitude of vibrations. Once, the body stops vibrating it longer produces ant sound.

Sound requires a medium for propagation. It does not travel in vacuum. Sound waves can travel through air, liquid and even through solids. Air acts a medium for sound propagation and we can hear each other well. 

Dolphins and whales communicate in water.

Special organs have been designed for receiving the sound waves. The brain interpret these waves into sounds that we hear.

Our hearing organs are ears. Ears are specially designed to grab and transit sound vibrations to our brain. The outer funnel like part of the ear collects the sound waves and send them through a long canal to the inner part. These vibrations reach a thin stretched membrane called eardrum. When these vibrations touch eardrum the eardrum starts vibrating and sends these vibrations to inner ear, from which brain receives the vibration. In this way one becomes able to hear various sounds. 

The below figure shows the structure of ears. 

frequency

vacuum

time period

20

20,000

music

noise

20 mm

amplitude

Decibel

frequency

A.

20 Hz to 20,000 Hz

A.

frequency

D.

vacuum

C.

m

A.

frequency

B.

20 mm

D.

1/5 second

B.

of more frequency

D.

all of these

C.

loudness

(i) The figures  given are:
(a) Drum (b) Whistle

(ii)

(a) Drum produces low pitched sound

(b) Whistle produces high pitched sound.