Characteristics of sound wave - class-VIII

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.

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. 

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.

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.

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 ,

The characteristics of a sound are :

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

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 . 

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 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.

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

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

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.

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

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.

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

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.

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 amplitude, frequency and wavelength.

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. 

Periodic Motion  is repeated at regular intervals

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. 

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

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.

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

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

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 

Except sound wave, all other options are electromagnetic waves.

We know that ,

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

The human ear can typically detect sound frequencies in the range of 20 Hz to 20,000 Hz.

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 .

The unit of frequency is Hz. 

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.

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 $I \propto a^{2}$

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 } $

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

Lungs are used to filter the oxygen from air .

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 .

Velocity of sound is proportional to the square root of absolute temperature (T). 127 C = 400 K. A 900 F increase is 500 C, so the new temperature is 127 + 500 = 627 C = 900 K. The ratio of velocities is sqrt(900/400) = 1.5. Thus, 200 * 1.5 = 300 m/s.

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.

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

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.

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

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