0

Characteristics of sound wave - class-VIII

Description: characteristics of sound wave
Number of Questions: 52
Created by:
Tags: physics world of sounds sound
Attempted 0/52 Correct 0 Score 0

Fill in the blank.

When sound travels in a medium _______ travels in form of a wave.

  1. the source

  2. the particles of the medium

  3. the disturbance

  4. the medium


Correct Option: C
Explanation:

When sound travels in a medium the disturbance travels in form of a wave.
Sound is produced when something vibrates. That is, a disturbance is produced. The vibrating body or disturbance causes the medium (water, air, etc.) around it to vibrate. Vibrations in air are called traveling longitudinal waves, which we can hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively.

The sound waves in a medium are characterised by the

  1. linear motion of particle in the medium

  2. rotatory motion of particles in the medium

  3. oscillatory motion of particles in the medium

  4. none of the above


Correct Option: C
Explanation:

Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, that is in an oscillatory motion, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. 

State whether given statement is True or False
A wave is a disturbance that moves through a medium when the particles of the medium set neighboring particles into motion.

  1. True

  2. False


Correct Option: A
Explanation:

Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, that is in an oscillatory motion, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. Here, the sound wave does not move the particles of the medium from one place to another but only the vibration or the disturbance moves. 
Hence, the statement is true.

Fill in the blank. 

In a wave, the particles of the medium do not move forward themselves, but the _________ is carried forward.

  1. disturbance

  2. frequency

  3. amplitude

  4. velocity


Correct Option: A
Explanation:

In a wave, the particles of the medium do not move forward themselves, but the disturbance is carried forward.
Sound is produced when something vibrates. That is, a disturbance is produced.

Which of the following is NOT correct?

  1. more oscillation per second, higher time period

  2. greater amplitude greater loudness

  3. higher pitch, higher frequency of vibration

  4. more the value of decibel, higher is the noise


Correct Option: A
Explanation:

Time period $T$ is defined as time taken to complete one oscillation , and frequency $f$ of a wave is defined as the number of oscillations per second ,

                     therefore , $T=1/f$  ,
which gives , more oscillations per second i.e. higher frequency , means smaller time period .

A person can be identified by the quality of sound produced by him. The characteristic of a sound can be determined by:

  1. amplitude

  2. frequency

  3. loudness

  4. all of the above


Correct Option: D
Explanation:

The characteristics of a sound are :

(i) Loudness or intensity : it distinguishes between a loud or faint sound , and intensity , depends upon amplitude of sound waves .
(ii) Pitch : it distinguishes a sharp sound from a dull sound and pitch depends upon frequency.
(iii) Quality: it distinguishes between sounds generated by two sources .

Which of the following statement is NOT correct?

  1. loudness of sound is determined by the amount of energy received by the ear per unit time

  2. pitch doesn't depend upon the amount of energy

  3. loudness changes with change of frequency

  4. pitch changes with change in frequency


Correct Option: C
Explanation:

Among all of the above only loudness changes with frequency is the wrong statement as loudness doesn't change with the change of frequency.

Which of the following statements is not true about a sound wave ?

  1. Sound travels faster in steel than in air

  2. Sound is a longitudinal wave

  3. The speed of sound in gas is not affected by a change in pressure of the gas

  4. The speed of sound in a gas decreases with increases in the temperature of the gas


Correct Option: D
Explanation:
A- Sound travel faster in solid than in gas. Here still is solid and air is gas.
B- Sound is a longitudinal wave as it can travels from one point to another point by to and fro.
C- Speed of sound in gas in independent of pressure and hence the answer.
D- The speed of the sound in a gas increases with the increasing in temperature of the gas. 
Hence D is incorrect ..

Microphone is used to convert

  1. Electrical energy into sound energy

  2. Sound energy into electrical energy

  3. Sound energy into mechanical energy

  4. Sound energy into chemical energy


Correct Option: B
Explanation:

When we speak on a microphone , our voice (sound energy) is converted in electrical signals (electrical energy) ,which can be transmitted through a wire to a distance . 

Sound waves in the air don't show ______?

  1. Polarisation

  2. Diffraction

  3. Refraction

  4. Rreflection


Correct Option: A
Explanation:

Answer is A.

Sound waves in air travel parallel to the direction that the particles within it oscillate it (definition of a longitudinal wave) - it propagates in 1 dimensional direction. Transverse waves have 2 components (and electric E component, and a magnetic M component). these components propagate at right angles to each other (i.e. it travels in two dimensions). Therefore it is possible to polarize transverse waves. 
Sound waves can be polarized in special conditions.In a solid medium, sound waves can be transverse waves, and in this scenario, the polarization is associated with the direction of the shear stress in the plane perpendicular to the propagation direction.
Hence, Sound waves in air do not show polarization.

Sound is a form of energy. True or false.

  1. True

  2. False


Correct Option: A
Explanation:

Sound is the movement of energy through substances in longitudinal (compression or rarefaction) waves. Sound is produced when a force causes an object or substance to vibrate. That is, the energy is transferred through the substance in a wave. So, sound is a form of energy.

Characteristic of sound which enables us to distinguish between two sound of same loudness and pitch :

  1. quality

  2. timbre

  3. amplitude

  4. a and b


Correct Option: D
Explanation:

 Quality is that characteristic of sound which enables us to distinguish between two sounds from two sources , even of the same frequency (pitch) and loudness . Quality is also called timbre . So option a and b are correct .

Sound is

  1. 1-D wave

  2. 2-D wave

  3. 3-D wave

  4. none


Correct Option: C
Explanation:

Sound energy is transferred in space in all directions. So it is a 3-D wave. Light waves are 3-D wave.

Sound wave can be described graphically by

  1. velocity displacement graph

  2. displacement time graph

  3. density distance graph

  4. amplitude velocity graph


Correct Option: C
Explanation:

A longitudinal wave, eg., Sound wave can be described by a density-distance graph. In density time graph, particle density of the medium is plotted on y axis where as time on the x axis

In density time graph

  1. particle density of the medium is plotted on y axis where as time on the x axis

  2. time on the y axis, particle density on x axis

  3. both a and b can be done interchangeably

  4. can't be plotted 


Correct Option: A
Explanation:

The density time graph for a longitudinal wave is drawn by plotting the particle density on the medium at any point on the wave on the y axis against time on the x axis.

In wave motion particles of the medium

  1. move from one place to another

  2. do not move from one place to another

  3. vibrate about their mean positions

  4. vibrate away from their mean position


Correct Option: C
Explanation:

When a wave passes through a medium, the particles of the medium vibrate according to the wave about the mean positions.

During a wave motion 

  1. no transfer of matter occurrs through the medium

  2. energy is transferred from one part of the medium to another

  3. both a and b occurs

  4. none of the above


Correct Option: C
Explanation:

During a wave motion only energy is transferred no transfer of matter occurs through the medium. Only vibrations travels not the air.

Sound wave is a

  1. Mechanical wave

  2. Non mechanical wave

  3. Progressive wave

  4. a and c


Correct Option: D
Explanation:

On the basis of necessity of medium, sound is a mechanical wave, because it needs a material medium for its transmission and on the basis of energy propagation, it is a progressive wave.

Peak of the density/Pressure - distance curve represent

  1. maximum rarefaction

  2. maximum compression

  3. minimum compression

  4. minimum rarefaction


Correct Option: B
Explanation:

The peak represents the region of maximum compression. Thus, compressions are the regions where pressure/density is high.

Mark the correct statement

  1. Hard surfaces are good reflectors of sound

  2. Soft surfaces are poor reflectors of sound

  3. Bad reflectors of sound are good absorbers of sound

  4. All the above are true


Correct Option: D
Explanation:

Sound is not reflected equally from different materials. Hard surfaces reflect more sound. Hard surfaces are good reflectors of sound. 
Soft or porous surfaces are poor reflectors of sound. Bad reflectors of sound are good absorbers of sound. These sound absorbing materials are used to cover walls, ceilings etc.

Explain why, if we strike a table lightly, we hear a soft sound but if we hit the table hard, a loud sound is heard.

  1. When a table is striked lightly,vibrations are produced with less amplitude

  2. When the table is strikes hard,the amplitude is high

  3. Both

  4. None


Correct Option: C
Explanation:

If we strike a table lightly the vibrations produced have less amplitude than when we strike the table hard. Since loudness depends on amplitude, soft sound is heard when we strike lightly.

By studying sound waves, we may come to know about its:

  1. amplitude only

  2. frequency and wavelength Only

  3. amplitude, frequency and wavelength

  4. amplitude and wavelength only


Correct Option: C
Explanation:

By studying sound waves, we may come to know about its amplitude, frequency and wavelength.

Which are the two properties that affect wave speed ?

  1. Inertial properties and elastic properties

  2. Mass properties and elastic properties

  3. Inertial properties and bending properties

  4. Bending properties and elastic properties


Correct Option: A
Explanation:

In a wave, particles are moving from one place to another and again come back to the same place due to inertial properties and due to elastic properties  the wave vibrates. 

The motion that is repeated at regular intervals is termed as

  1. Vibration

  2. Ventilation

  3. Oscillation

  4. Periodic Motion


Correct Option: D
Explanation:

Periodic Motion  is repeated at regular intervals

Which of the following is not a characteristics of mechanical waves? 

  1. They consist of disturbances or oscillations of a medium 

  2. They transport energy.

  3. They travel in a direction that is at right angles to the direction of the particles of the medium. 

  4. They are created by vibrating source. 


Correct Option: C
Explanation:

All of the above are the characteristics except mechanical waves travel in a direction that is at right angles to the direction of the particles of the medium. 

Find out the relationship between the frequency and amplitude of a sound wave?

  1. Frequency is proportional to amplitude

  2. Frequency is proportional to the square of the amplitude

  3. Frequency is inversely proportional to amplitude

  4. Frequency is inversely proportional to the square of the amplitude

  5. Frequency and amplitude are independent


Correct Option: E
Explanation:

Frequency of a wave is $f=1/T$ where T be the time period of the wave.

As time period does not depend on the amplitude so frequency is also independent of amplitude.  

Sound waves cannot travel in:

  1. air

  2. metal

  3. vacuum

  4. water

  5. wood


Correct Option: C
Explanation:

Sound waves are mechanical waves and we know from the properties of mechanical waves that they require medium to propagate , therefore sound waves cannot travel in vacuum.

Compressional wave among the following is?

  1. X-ray

  2. Cosmic ray

  3. Radio wave

  4. Light wave

  5. Sound wave


Correct Option: E
Explanation:

X-ray, cosmic ray, radio wave, light wave, they all  are electromagnetic waves and we know that an electromagnetic wave is always  a transverse wave, on the other hand sound wave is a mechanical longitudinal wave which propagates in a medium with compressions and rarefactions. Therefore, sound wave is a compressional wave among them.

Sound waves do not exhibit polarization because, unlike light waves, they are not:

  1. longitudinal

  2. coherent

  3. dispersive

  4. transverse

  5. refractive


Correct Option: D
Explanation:

In polarization the vibrations of electric vector of light are restricted by a polariser in a single plane  because vibrations are perpendicular to the propagation of light ,  as light is a transverse wave .
Polarization is the phenomenon of transverse waves only , it does not happen in longitudinal waves  , as sound waves are longitudinal waves in which vibrations are in the direction of propagation of wave so they pass the polariser without any change and doesn't experience any polarization . 

Which type of wave can be diffused by Acoustic diffusers?

  1. sound waves

  2. light waves

  3. water waves

  4. microwaves

  5. ultraviolet rays


Correct Option: A
Explanation:

Sound waves can be diffused by Acoustic diffusers but not the other given waves. 

Sound waves can diffract easily because

  1. Their wavelength is very small

  2. Their wavelength is large

  3. It can reflect

  4. It can refract


Correct Option: B
Explanation:

Having a very large wavelength made the waves to bend more, when they meet on obstacle.

Time taken to complete a wave is called as

  1. Period 

  2. Span

  3. Life 

  4. Duration 


Correct Option: A
Explanation:

The time taken to complete a wave is termed as period which can be written as $T=\dfrac{1}{f}$ T= time period ; f= frequency 

The wavelength of light absorbed by $Pr$ form of phytochrome is:-

  1. $620 nm$

  2. $640 nm$

  3. $680 nm$

  4. $720 nm$


Correct Option: C
Explanation:

The Pr form absorbs light between $660$ to $680 nm$ and absorbs at a peak of $666 nm$. It is the form synthesized in dark-grown seedlings. When Pr absorbs red light, it is converted to the $Pfr$ form.

Which of the following type of waves is different from others? 

  1. Light waves

  2. X-rays

  3. Radio waves

  4. Sound waves


Correct Option: D
Explanation:

Except sound wave, all other options are electromagnetic waves.

The frequency of a man's voice is $300Hz$ and its wavelength is $1$ meter. If the wavelength of a child's voice is $1.5m$, then the frequency of the child's voice is:

  1. $200Hz$

  2. $150Hz$

  3. $400Hz$

  4. $350Hz$


Correct Option: A
Explanation:

We know that ,

$f=\dfrac{c}{\lambda}$
So,
$\dfrac{f _{man's voice}}{f _{child's voice}}=\dfrac{\dfrac{c}{\lambda _{man's voice}}}{\dfrac{c}{\lambda _{child's voice}}}$
$\dfrac{f _{man's voice}}{f _{child's voice}}$=$\dfrac{\lambda _{child's voice}}{\lambda _{man's voice}}$     
$\dfrac{300}{f _{child's voice}}=\dfrac{1.5}{1}$
$f _{child's voice}=\dfrac{300}{1.5}$
$f _{child's voice}=200 Hz$
  

two waves of same frequency and of intensity ${I} _{0}$ and $9{I} _{0}$ produces interference. If at a certain point the resultant intensity is $7{I} _{0}$ then the minimum phase difference between the two sound waves will be

  1. ${90}^{0}$

  2. ${150}^{0}$

  3. ${120}^{0}$

  4. ${100}^{0}$


Correct Option: C
Explanation:

$\begin{array}{l} 7{ I _{ o } }={ I _{ o } }+a{ I _{ o } }+2\sqrt { { I _{ o } } } \sqrt { x{ I _{ o } } } \cos  \Delta \phi  \ \Rightarrow 7{ I _{ o } }=10{ I _{ o } }+6\cos  \Delta \phi  \ \Rightarrow -3{ I _{ o } }=6\cos  \Delta \phi  \ \cos  \Delta \phi ={ { -1 } }{ 2 } \ \Delta \phi =\dfrac { { 2\pi  } }{ 3 } =\dfrac { { 2\times 180 } }{ 3 } ={ 120^{ 0 } } \ Hence, \ option\, \, C\, \, is\, \, correct\, \, answer. \end{array}$

Sound frequency that can be detected by the human ear is 

  1. $1500\ Hz$

  2. $20,000\ Hz$

  3. $12,000\ Hz$

  4. $22,000\ Hz$


Correct Option: B

When you speak to your friend which of the following quantities have a unique value in the sound produced by both the boys?

  1. amplitude

  2. wave velocity

  3. frequency

  4. wavelength


Correct Option: B
Explanation:

Out of the given quantities , wave velocity has a unique value . Because both the friends are producing the sound in the same medium , and wave velocity depends upon medium , which is not changing here .

Amplitude of the sounds depends upon the energy given by any of the friends to sound , so it may change .
Frequency of sound depends upon the thickness of vocal cords of two friends , so it also may vary . Now wavelength $\lambda \propto 1/f$, for a constant velocity , when frequency $f$ changes , wavelength will also change .

What is the unit of frequency?

  1. Hz

  2. Watt

  3. Volt

  4. $m^{-1}$


Correct Option: A
Explanation:

The unit of frequency is Hz. 

Sound is produced by a

  1. vibrating body

  2. moving body

  3. oscillating body

  4. both A and C


Correct Option: A,B,C
Explanation:

Sound is produced by a vibrating body.
Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in air are called travelling longitudinal waves, which we can hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively.

If one puts one ears to the steel rail, the sound of a coming train can be heard even when the train cannot be seen. One can conclude from this observation that
A. Sound travels faster in steel than in air.
B. Amplitude of sound in the rail is much larger than in air.
C. Sound can travel larger distance in solids than in air.
D. Quality of sound in rail is better than in air.
The reasonable conclusion are

  1. A and C

  2. A and B

  3. B and C

  4. None of these


Correct Option: B
Explanation:

Velocity of sound is maximum in solids and least in gases
$ V _{gas} < V _{liquid} < V _{solid} $
Intensity would also be much lower in air as $I \propto a^{2}$

How is the frequency of a wave related to its time period?

  1. $\ v=\displaystyle\frac{1}{T}$

  2. $\ T=\displaystyle\frac{1}{v}$

  3. $\ v T=\displaystyle{1}$

  4. All the above


Correct Option: D
Explanation:

Frequency is the number of occurrences of a repeating event per unit time. The Time period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency.

That is, $T=\dfrac { 1 }{ f } \quad \quad or\quad \quad f=\dfrac { 1 }{ T } $

Longitudinal waves are possible in 

  1. solids

  2. liquids

  3. gases

  4. All of these


Correct Option: D
Explanation:

For propagation of sound wave, medium is necessarry it might be in any form. Like solid liquid or gas.

The voices of Men, Women and children differ because of difference in their

  1. Lungs

  2. Wind pipr

  3. Vocal chords

  4. Larynx


Correct Option: C
Explanation:

Lungs are used to filter the oxygen from air .

Wind pipe provides a path for air to go inside the lungs .
Larynx is responsible for the production of sound .
Vocal cords are inside the larynx , and their thickness decides the frequency of sound (shrill or grave ) , by which we can differentiate between the voices of a man (grave) , women and children(shrill) .

When longitudinal wave propagates through a medium, then the physical quantities propagating in the direction of wave are

  1. Energy

  2. Energy, momentum and mass

  3. Energy and mass

  4. Energy and momentum


Correct Option: A
Explanation:

When a disturbance is produced in a medium , it is transported by oscillating particles of the medium , the disturbance is a kind of energy and carried by oscillating particles by passing it to the next particle , in this way a longitudinal wave propagates, therefore energy propagates in a longitudinal wave .

As there is no net movement of the medium particles in the propagation of wave , they just vibrate about the centers of rarefaction and compressions , therefore momentum is not transferred in a longitudinal wave . Thus only energy is propagating in the direction of wave. 

If the velocity of sound in a gas is $200 {ms}^{-1}$ when the temperature is $127^0  C$, then the velocity of sound in the same gas when temperature is increased by $900^0  F$ is ______ ${ms}^{-1}$

  1. $200\sqrt{3}$

  2. 300

  3. $100\sqrt{5}$

  4. 450


Correct Option: B

A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound :

  1. is more dense than air and thus has more inertia, causing the bunching up of sound

  2. waves have a speed which is dependent only upon the properties of the medium

  3. is like all waves; it is able to bend into the regions of space behind obstacles

  4. is able to reflect off fixed ends and interfere with incident waves vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations


Correct Option: D
Explanation:

These compressions and rarefactions result because sound is able to reflect off fixed ends and interfere with incident waves vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations. Compressions are the regions of high density and rarefactions are regions of low density.

The speed of highly penetrating ultrasonic waves is :

  1. Lower than those of audible sound waves

  2. Higher than those of audible sound wave

  3. Much higher than those of audible sound waves

  4. Same as those of audible sound waves


Correct Option: B
Explanation:

Speed of highly penetrating ultrasonic waves is greater than 20,000Hz equal to $10^7$Hz

Suppose a stick is struck against a frying pan in vacuum. Which of the following is/are true?

  1. the frying pan vibrate

  2. we be able to hear the sound

  3. we can hear the sound just for few minutes 

  4. None of the above


Correct Option: A
Explanation:

Sounds are made by vibrations. Some vibrations are easy to see.
In this case, a stick is struck against a frying pan in vacuum. The frying pan vibrates. But this happens in vacuum. Sound waves require a medium to travel through. Outer space is a vacuum, and therefore it is not heard.
Hence, the sound created by the stick and frying pan is not heard.

Through which of the following media does sound travel the fastest?

  1. Cold water

  2. Warm air

  3. Cold air

  4. Steel


Correct Option: D
Explanation:

Speed of sound is depends upon the elasticity of the material. In the given option steel have highest elasticity so sound will travel fastest through steel.

The velocity of sound in air is not affected by change in 

  1. the moisture content of the air.

  2. the temperature of air.

  3. the atmospheric pressure.

  4. the composition of air.


Correct Option: C
Explanation:

The speed of sound depends on temperature. The formula relating speed of sound and temperature is as follows:

$v = 331 + 0.6 \times T$, where $T$ is temperature in absolute scale and $v$ is in $m/s$.
Humidity has little effect on the speed of sound.
Air pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out each other, leaving only the effect of temperature.
Composition of air has also almost no effect on the speed of sound.

Consider the following
l. Waves created on the surfaces of a water pond by a vibrating source.
ll. Wave created by an oscillating electric field in air.
lll. Sound waves travelling under water. 
Which of these can be polarized

  1. l and ll

  2. ll only

  3. ll and lll

  4. l, ll, and lll


Correct Option: A
Explanation:

Sound waves are longitude and can not be polarized. Answer A

- Hide questions