Tag: sound waves are longitudinal waves

Questions Related to sound waves are longitudinal waves

Transverse mechanical wave can travel in :

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. Iron rod

  2. Hydrogen gas

  3. Water

  4. Stretched string

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Correct Option: A,C,D
Explanation:

Transverse wave is that wave which vibrate the particles of medium in the medium in the $\bot $ar direction to the direction of wave propegation.

Exp :-    $\left( 1. \right) $ A wave on string.
             $\left( 2. \right) $ Ripples on water waves.
             $\left( 3. \right) $ EM wave.
             $\left( 4. \right) $ In metals like iron rod.

In brass, the velocity of longitudinal waves is $100\ times$ the velocity of transverse waves. If $Y = 1 \times 10 ^ { 11 }\ N/m^2,$ then the stress in the wire is

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. $10 ^ { 7 }/ N/m^2$

  2. $10 ^ { 8 }/ N/m^2$

  3. $10 ^ { 9 }/ N/m^2$

  4. $10 ^ { 10 }/ N/m^2$

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Correct Option: A
Explanation:

Velocity of transverse wave ${V _T} = \sqrt {\left( {\frac{T}{m}} \right)} $

${V _T} = \sqrt {\left{ {\frac{T}{{\left( {\pi {r^2}\rho } \right)}}} \right}} .............\left( 1 \right)$
Velocity of longitudinal wave ${V _L} = \sqrt {\frac{Y}{\rho }} ...............\left( 2 \right)$
Given:
$\begin{array}{l} { V _{ L } }=100{ V _{ T } } \ \therefore \sqrt { \frac { Y }{ \rho  }  } =100\sqrt { \left{ { \frac { T }{ { \left( { \pi { r^{ 2 } }\rho  } \right)  } }  } \right}  }  \ \therefore Y={ \left( { 100 } \right) ^{ 2 } }\times \left{ { \frac { T }{ { \left( { \pi { r^{ 2 } } } \right)  } }  } \right}  \end{array}$
As stress $ = \left{ {\frac{{\left( {force} \right)}}{{\left( {area} \right)}}} \right} = \left{ {\frac{T}{{\left( {\pi {r^2}} \right)}}} \right}$
$\therefore Y = {10^4} \times $stress
$\therefore$ stress $ = \left( {\frac{Y}{{{{10}^4}}}} \right) = \left{ {\frac{{\left( {1 \times {{10}^{11}}} \right)}}{{\left( {{{10}^4}} \right)}}} \right} = 1 \times {10^7}\,\,N/{m^2}$

A wave moving in a gas

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. must be longitudinal

  2. may be longitudinal

  3. must be transverse

  4. may be transverse

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Correct Option: A

Longitudinal waves do not exhibit ?

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. Refraction

  2. reflaction

  3. Diffraction

  4. Polarization

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Correct Option: D

Choose the correct options for longitudinal wave

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. maximum pressure variation is BAk

  2. maximum density variation is pAk

  3. pressure equation and density equation are in phase

  4. pressure equation and displacement equation are out of phase

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Correct Option: C

A longitudinal wave consists of :

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. crest and trough in the medium

  2. compression and rarefraction in the medium

  3. both (a) & (b)

  4. nither (a) nor (b)

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Correct Option: A

Find the incorrect statement

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. Ultrasound can be used to determine the sex of the unborn baby (embryo)

  2. Ultrasound can be used to keep away rodents in cold storage

  3. Ultrasound can be used to detect even bone fractures

  4. Ultrasound travels faster than sound

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Correct Option: C,D
Explanation:

Ultrasound frequency used for imaging is about $5 MHz.$
The corresponding wavelength is $\lambda = \dfrac{v}{\nu}=\dfrac{1540 \text{m/s}}{5\times 10^6} = 0.3mm$ 
Here speed of ultrasound in tissue is taken to be $1540 m/s$.
So ultrasound can not be used for bone fractures as it bone fracture can have size of few microns.
Ultrasound does not travel faster than sound. Sound speed does not depend on frequency.
$v=\nu \lambda$ if $\nu$ is higher, $\lambda$ becomes smaller and $v$ remains constant.

A metal bar clamped at its center resonates in its fundamental mode to produce longitudinal waves of frequency 4 kHz.Now the clamp is moved to one end. If ${f _1}\;{\text{and}}\;{f _2}$ be the frequencies of first overtone and second overtone respectively then, 

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. $3{f _2} = 5{f _1}$

  2. ${f _2} = 2{f _1}$

  3. $3{f _1} = 5{f _2}$

  4. $2{f _2} = {f _1}$

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Correct Option: A
Explanation:

$\begin{array}{l} { f _{ 1 } }=3f \ { f _{ 2 } }=5f \ \Rightarrow 5{ f _{ 1 } }=3{ f _{ 2 } } \ Hence, \ option\, \, A\, \, is\, \, correct\, \, answer. \end{array}$

A longitudinal wave is reflected from the surface of a rigid wall. Its phase changes by :

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. 0 rad

  2. $\pi $ rad

  3. $\pi $/2 rad

  4. 2 $\pi $ rad

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Correct Option: B

In a stationary wave represented by $y = a \sin wt \cos kx$, amplitude of the component progressive wave is

physics study of sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

  1. $\frac{a}{2}$

  2. $a$

  3. $2a$

  4. $a^2$

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Correct Option: A