Physics · Science General

Acoustics and Sound Waves

2,006 Questions

Acoustics and sound waves deal with mechanical vibrations traveling through media like air and water. Key concepts include wave reflection, beats, echoes, the Mach number, and infrasound. These physics fundamentals are regularly tested in general science sections of multiple competitive exams.

Sound wave propagationEchoes and reflectionWave interferenceMach numberInfrasound frequency

Acoustics and Sound Waves Questions

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

Vibrations of period 0.25 s propagate along a straight line at a velocity of 48 cm/s. One second after the emergence of vibrations at the initial point, displacement of the point, 47 cm from it is found to be 3 cm. Then,

  1. amplitude of vibrations is 6 cm.
  2. amplitude of vibrations is $3 \sqrt{2} cm.$

  3. amplitude of vibrations is 3 cm.

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The wavelength of the wave can be found by using $\dfrac{\lambda}{T}=v$

$\implies \lambda=vT=48cm/s\times 0.25s=12cm$
Four full wavelengths complete at a distance of 48cm.
Thus a point 47cm lag by a phase difference of $\dfrac{2\pi}{\lambda}(48cm-47cm)=\dfrac{\pi}{6}$
Let the amplitude of vibrations be $A$.
Thus the displacement at the given point=$Asin(\dfrac{\pi}{6})=\dfrac{A}{2}=3cm$
$\implies A=6cm$
Thus correct answer is option A.

Multiple choice problems on properties of waves terms and defination used in wave motion oscillation and waves waves physics

The displacement of an elastic wave is given by the function $y= 3\ sin \omega t+4\ cos\omega t$, where $y$ is in $cm$ and $t$ is in $s$. The resultant amplitude is 

  1. $3 cm$
  2. $ 4 cm$
  3. $ 5 cm$
  4. $7 cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here, we have given: $y=3sin\omega t+4cos\omega t$


So, two components are there, $3sin\omega t $ and $4cos\omega t$


where, individual amplitudes are given by
$A _1= 3 cms$ and $A _2=4 cms .$

so , resultant amplitude will be, 
$A=\sqrt{A _1^2 +A _2^2}=\sqrt{3^2+4^2}$

$A=5 cms$


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

When a sound wave goes from one medium to another , the quantity that remains unchanged is

  1. Frequency

  2. amplitude

  3. wavelength

  4. speed
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The electric and magnetic fields have to remain continuous at the refractive index boundary. If the frequency changed, the light at each side of the boundary would be continuously changing it's relative phase and there would be no way to match the fields.
Furthermore, for conservation of energy frequency should remain same.
Energy $E' = h\nu'$ inside the glass must be equal to the energy outside, so
$E = E'$ gives
$h\nu = h\nu'$
so $\nu = \nu'$
the frequency in the medium is equal to that of outside.
Ans: A

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

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, 

  1. $3{f _2} = 5{f _1}$
  2. ${f _2} = 2{f _1}$
  3. $3{f _1} = 5{f _2}$
  4. $2{f _2} = {f _1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

When a tuning fork vibrates, the waves produced in the stem are:

  1. longitudinal

  2. transverse

  3. both (a) and (b)

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When tuning fork is sounded by striking its one end then the prongs vibrate in and out and stem vibrate up and down. Hence, vibration of prongs are transverse and those of stem are longitudinal. 

Hence Option A is correct

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

When you speak to your friend, the quantity having a non unique value in the sound produced is

  1. amplitude

  2. wave velocity

  3. frequency

  4. wavelength
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Amplitude and frequency depend on source and as frequency is different, wavelength also has to be different to maintain same speed as speed is constant for a medium in a particular condition.