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Question 1

Define sound.

Sound helps to communicate with one another, it travels from one point to another in the form of wave. It is also defined as sensation of hearing.


Question 2

Which object is vibrating when the following sounds are produced?

(i) The sound of a sitar or veena
(ii) The sound of the tabla
(iii) The sound of a school bell.
(iv) The buzzing of a bee or a mosquito.
(v) The sound of a bursting balloon.
(vi) The radio


(i) Strings of sitar or veena vibrate to produce sound.

(ii) The skin of the table vibrate to produce sound.

(iii) The disc of the bell when beated with hammer vibrate to produce sound.

(iv) Winds of the mosquito or a bee vibrate to produce sound.

(v) Air vibrates to produce sound.

(vi) Diagragm of the speaker, in the radio vibrates to produce sound.

Question 3

Define amplitude.


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


Question 4

What is called time period?

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


Question 5

Define frequency.

It is the number of vibrations produced by a vibrating body in one second.


Question 6

What are ultrasonic waves?

It is the sound of frequencies more than 20000 hertz. We cannot hear such sounds.


Question 7

What are radio waves?

These are the types of waves which need no medium to travel.


Question 8

What is velocity of sound?

It is the distance traveled by sound waves in unit time. The velocity of sound at 20° C temperature is considered approximately 340 m/sec.


Question 9

What is an echo?

The reflected sound if heard distinctly from the original sound is called an echo. It can also be defined as sound heard after reflection from a high wall or obstacle.


Question 10

The maximum displacement of an oscillating object is called the _____.



Question 11

The number of oscillations per second made by the object is called the



Question 12

Define Hertz.

Frequency of a vibration or oscillation is measured in hertz. It is the unit of frequency.


Question 13

What do you mean by the term loudness?

Loudness of sound is determined by its amplitude.


Question 14

What is pitch of the sound?

It is characteristic of sound depending upon its frequency. Different frequencies produce different pitch of sound.


Question 15

We hear sound only of its frequency is greater than ________ and lower than ________.

20 hertz, 20000 hertz.


Question 16

A taut membrane produces sound of ________ frequency than a loose one.



Question 17

What frequencies are heard and produced by dogs and bats respectively?

Dogs can hear frequencies up to 40,000 Hz while bats can produce and hear frequencies up to 70,000 Hz.


Question 18

Pendulum A makes 14 oscillations in five seconds and pendulum B makes 10 oscillations in three seconds. Which has a higher frequency? Express the frequency of each pendulum in hertz.


Frequency of

Frequency of

Pendulum B has higher frequency.

Question 19

What is the range of audible frequencies for a normal human ear?


sounds of range 20 hertz to 20,000 hertz are audible range for human ear.


Question 20

Give two applications of ultrasound in medical sciences.

Ultrasound is used as diagnostic tool in medical science and in relieving pain, in joints and muscles.


Question 21

Give two applications of ultrasound in industries.

Ultrasound is used to detect flaws in metals and structures and to test the thickness of various parts.


Question 22

What is noise?

The sound which is loud and barsh, which annoys us and reduces our work efficiency is called noise.


Question 23

What is called musical sound?

Musical sound is one which produces a pleasing sensation.


Question 24

What do you understand by stringed instruments?

Those instruments have taut strings, which vibrate when they are plucked, sruck, or played with a bow.


Question 25

Why does a table with tight membrane vibrates at a higher itch than a tabla with a loose membrane?

A tight membrane vibrates at a much higher frequency than a loose one, so that the sound produced with tight membrane has a higher pitch.

Question 26

On which principle, the Indian musical instrument "Jal Tarang" works?

Jal Tarang works on the principle that the quality of the sound changes with the change in its frequency. Metal tumblers filled with water up to different heights, give vibrations of different frequencies, hence produce different types of sounds.

Question 27

Why do our steps do not produce loud sound if we walk on a carpet floor?

When we walk on a carpet floor, the amplitude of vibrations of the floor is reduced and the sound of our steps becomes feeble.


Question 28

How loud sound is harmful to us?

A loud sound is harmful to us. It can damage our eardrum and make us deaf partially or wholly.


Question 29

What type of voice is produced when the vocal cards are tight and thin?

The voice of high frequency is produced.


Question 30

What is the normal length of vocal cords in man?

The vocal cord of a man is about 20 mm long.


Question 31

Do all animals produce sound by vocal cords?

No all animals do not produce sound by vocal cords.


Question 32

How is sound produced in humans?

In humans, voice box or the larynx is the most important source of sound. Two ligaments, known as vocal cords, are stretched across the larynx 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 voice.


Question 33

Define vocal cords.

These are the two ligaments stretched across the larynx in such a way that it leaves a narrow slit between them for the passage of air.


Question 34

How the muscles attached to vocal cards regulate sound?

Muscles attached to the vocal cords may make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when these are loose and thick.


Question 35

Why the voice of men, women and children are different?

The vocal cords in men are about 20mm long. In women there are about 5mm shorter. Children have very short vocal cords. That is the reason that the voice of men, women and children are different.


Question 36

What is eardrum? How does it is play an important role in hearing?

We hear sound through our ears. The shape of the outer part of ear is like a funnel, when sound enters in it, travels down a canal at the end of which a thin membrane is stretched tightly. It is called the eardrum. It performs an important function

The eardrum is like a stretched rubber sheets. Sound vibrations make the eardrum vibrate (see fig 13.2) the eardrum send vibrations to the inner ear. From there, the signal goes t the brain. That is how we hear.

Question 37

On which property of vibrations does the loudness of sound depends?


The loudness of sound is determined by its amplitude. When the amplitude of a vibrating is large, the sound produced is loud. When the amplitude is small, the sound produce is feeble.


Question 38

Which property of vibrations determines the pitch of the sound? Explain giving some examples.

The frequency determines the shrillness or pitch of a sound. If the frequency of vibrations is higher we say that the sound has a higher pitch. If the frequency of vibration is lower, we say that the sound has a lower pitch. For example, the drum vibrates with a low frequency. Therefore, it produces a low pitched sound. On the other hand, a whistle has a high frequency and, therefore, produces a sound of higher pitch. A bird makes a high pitched sound whereas a lion makes a low pitched roar. However, the roar of a lions is very loud while the sound of bird is quite feeble.


Question 39

What is the audible range of frequencies for human beings? Explain.

Sounds of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear. Such sounds are called inaudible. On the higher side, sound of frequencies more than about 20, 000 vibrations per second (20kHz) are also not audible to the human ears. Thus, for human ears, the range of audible frequencies is roughly from 20.


Question 40

Which range of frequencies are used in ultrasound equipments? Explain various uses of ultrasound.

The ultrasound equipment, familiar for investigating and tracking many medical problems, works at frequencies higher than 20000 Hz. In industry, ultrasound is used for detecting flaws and cracks in metallic and other structures. Some animals can here sounds of frequencies higher than 20,000Hz. Dogs can also hear sound of frequencies higher than 20,000Hz. Some people use special high frequency whistles, which dogs have this ability. Therefore, the police uses high frequency whistles which dogs can her but human cannot.


Question 41

How does the loudness of sound depend upon the amplitude? Explain giving example.

Loudness of sound is proportional to the square of the amplitude of vibrations producing the sound. For example, if the amplitude becomes twice the loudness increases by a factor of 4.


Question 42

What is the unit of the loudness of sound? Explain giving the loudness of few sounds.

The loudness is expressed in a unit called decibel (dB). It is essentially a ratio if the actual loudness to some base loudness level. The base level is usually defined as that loudness of sound that the human ear can just perceive. The following table gives some idea of the loudness of sound coming from various sources.
Normal breathing 10 dB
Soft whisper (At 5m) 30 dB
Normal conversation 60 dB
Busy traffic 70 dB
Average factory 80 dB

At 80 dB the noise becomes physically painful.

Question 43

What is noise pollution? What are its major causes?

Presence of excessive or unwanted sounds in the atmosphere is called noise pollution. Major cause of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.


Question 44

What sources in the home may lead to noise?

At home, television and transistor at high volumes, some kitchen appliances, desert coolers, air-conditioners all contribute to noise pollution.


Question 45

What are the harms of noise pollution?

Presence of excessive noise in the surroundings may cause many health related problems. Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temporary or even permanent deafness.


Question 46

How can we control noise?

To control noise we must control the source of noise. For this silencing devices must be designed and installed in aircrafts engines, heavy transport vehicles, industrial machines and home appliances.


Question 47

How can the noise pollution be controlled in a residential area?

The noisy operations must be conducted away from any residential area. Noise producing industries should be set up away such area. Use of automobile horns be minimized. TV and music systems should be run at lower volumes. Plants must be planted along the roads and around buildings to minimize the harmful effects of noise pollution.

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