Physics

Wave Motion

536 Questions

Wave motion questions cover the principles of traveling and stationary waves, including their equations and intensities. The topics explore interference patterns, phase differences, and electromagnetic radiation speeds. Mastery of these concepts is vital for physics sections in engineering and civil services examinations.

Wave interferenceStanding wavesPhase differenceElectromagnetic radiationWave equations

Wave Motion Questions

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

A Sound wave with an amplitude of $ 3 \mathrm { cm }$ starts towards right from origin and gets reflected at a rigid wall after a second. If the velocity of  the wave is $ 340 \mathrm { ms } ^ { - 1 }$  and it has a wavelength of $ 2 \mathrm { m } $, the equations of incident and reflected waves respectively could be

  1. $\begin{array} { l } { y = 3 \times 10 ^ { - 2 } \sin \pi ( 340 t - x ) } \\ { y = - 3 \times 10 ^ { - 2 } \sin \pi ( 340 t + x ) \text { towards left } } \end{array}$
  2. $\begin{array} { l } { y = 3 \times 10 ^ { - 2 } \sin \pi ( 340 t + x ) } \\ { y = - 3 \times 10 ^ { - 2 } \sin \pi ( 340 t + x ) \text { towards left } } \end{array}$
  3. $\begin{array} { l } { y = 3 \times 10 ^ { - 2 } \sin \pi ( 340 t - x ) } \\ { y = - 3 \times 10 ^ { - 2 } \sin \pi ( 340 t - x ) \text { towards left } } \end{array}$
  4. $\begin{array} { l } { y = 3 \times 10 ^ { 2 } \sin \pi ( 340 t - x ) } \\ { I = 3 \times 10 ^ { - 2 } \sin \pi ( 340 t + x ) \text { towards left } } \end{array}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\begin{array}{l} y=\left( { 3\times { { 10 }^{ -2 } } } \right) \sin  \left( { \omega t-kx } \right)  \ \lambda =2m=\frac { { 2\pi  } }{ k }  \ \Rightarrow k=\pi  \ v=340\, m/s \ w=vk \ =240\pi  \ Now, \ y=\left( { 3\times { { 10 }^{ -2 } } } \right) \sin  \left( { 340\pi t-\pi x } \right) \, \, towards\, right \ and, \ y=\left( { 3\times { { 10 }^{ -2 } } } \right) \sin  \left( { 340\pi t+\pi x+\pi  } \right)  \ =-\left( { 3\times { { 10 }^{ -2 } } } \right) \sin  \left( { 340\pi t+\pi x } \right) \, \, \, \, \, \, \, towards\, \, left \ Hence,\, the\, option\, A\, is\, the\, correct\, answer. \end{array}$

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

Sound waves are propagating in a medium. The moduli of isothermal and adiabatic elasticity of the medium are $E _T$ and $E _S$ respectively. The velocity of sound wave is proportional to

  1. $\sqrt{E _T}$
  2. $\sqrt{E _S}$
  3. $E _T$
  4. $\displaystyle\frac{E _S}{E _T}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Velocity of sound $V _s$ is given by


${V _s}^2={[\dfrac{\delta{p}}{\delta{\rho}}]} _S=E _S$

$V _s \propto \sqrt{E _S}$

Option 'B' is correct.

Multiple choice speed of sound in gas speed of a travelling wave oscillation and waves waves physics

Ultrasonic, infrasonic and audio waves travel through a medium with speeds $V _{u}, V _{i}$ and $V _a$ respectively then,

  1. $V _{u}, V _{i}$ and $V _{a}$ are equal
  2. $V _{u} > V _{a}> V _{i}$
  3. $V _{u} < V _{a} < V _{i}$
  4. $ V _{a}< V _{u} $ and $V _{u} \approx V _{i} $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Velocity of sound wave in a medium is given by
$v= \sqrt{\frac{K}{\rho}}$ where K is the bulk modulus and $\rho$ is the density.
The classification of sound waves based on wavelength($\lambda$) is independent of speed of sound in the medium( speed depends on properties of a medium).
Hence, $V _u$, $V _i$ and $V _a$ are all equal.

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

Ocean waves of time period $0.01$ second have a speed $15 m/s$. What is the adjacent crest and the trough is:

  1. $15 \times 10^{-2} m$
  2. $7.5 \times 10^{-2} m$
  3. $3.25 \times 10^{-2} m$
  4. $30 \times 10^{-2} m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The distance between a crest and an adjacent trough is half the wavelength (lambda/2). Wavelength = speed * time period = 15 * 0.01 = 0.15 m. Half the wavelength is 0.075 m, which is 7.5 * 10^-2 m.

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

A transverse wave travelling on a taut string is represented by $y = 0.01 \sin 2 \pi ( 10 t - x )$ where y and x are in metre and t is in second. Then

  1. The speed of the wave is 10 m/s.
  2. Closest points on the string which differ in phase by $60^o$ are $\dfrac16\ m$ apart.
  3. Maximum particle speed is $\frac { \pi } { 5 } { m } / { s }$
  4. The phase of a certain point on the string changes by $120 ^ { \circ }$ is $\dfrac1{20} $seconds
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

What is the phase difference between two successive crests in the wave?

  1. $\pi$
  2. $\frac{\pi}{2}$
  3. $2\pi$
  4. $4\pi$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Phase difference between any two particles in a wave determines lack of harmony in the vibrating state of two particles, ie, how far one particle leads the other or lags behind the other. 
Relation of path difference and phase difference is given by
$\Delta \phi=\frac{2\pi}{\lambda}\times \Delta x$
where $\Delta x$ is path difference. 
But path difference between two crests
$\Delta x=\lambda$
Hence, $\Delta  \phi = \frac{2\pi}{\lambda}\times \lambda =2\pi$ 

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

The wave produced by a motor boat sailing in water are

  1. Transverse

  2. Longitudinal

  3. Longitudinal and Transverse

  4. Stationary
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The waves produced by a motorboat sailing in water are of both transverse and longitudinal type. Transverse waves are produced on the surface and longitudinal waves are produced deep inside the water.

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

Transverse mechanical wave can travel in

  1. Iron rod

  2. Hydrogen gas

  3. Water surface

  4. Stretched string
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

Transverse waves can travel only in solids and only along the surface of liquids, but not in the entire liquid. They can't travel in gases.

Since iron rod and stretched string are solids, transverse waves can travel in them.
Water surface being a liquid surface they can travel in it also.
Hydrogen gas being a gas, they can't travel in it.

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

Which of the following does not identify a necessary property of wave motion?

  1. transmission of energy

  2. periodic motion

  3. disturbance

  4. a material medium
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In any wave motion, energy is always transferred to the next particle which is succeeding the previous particle.  In a wave motion, particles are oscillating in a direction perpendicular to the direction of propagation or parallel. Since oscillation is a periodic motion,  we can say that periodic motion is always associated with the wave.  An oscillatory disturbance is always imparted the next and next particle and this is how the disturbance Travels across the particles.  Ordinary waves require a material medium for propagation. But electromagnetic waves do not require any material medium. They can also propagate through vacuum. Thus material medium is not a necessary condition for all wave motions.

Multiple choice physics properties of waves longitudinal and transverse waves travelling waves types of waves

During propagation of a plane progressive mechanical wave :

  1. all the particles are vibrating in the same phase

  2. amplitude of all the particles is equal

  3. particles of the medium execute S.H.M.

  4. wave velocity depends upon the nature of the medium
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

During propagation of a plane progressive mechanical wave amplitude of all the particles is equal, particle of the medium execute S.H.M, wave velocity depends upon the nature of the medium and all the particles are vibrating in the different phase.

Hence $B, C$ and $D$ are correct options.