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 physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

A replica of longitudinal waves can be best observed 

  1. by swinging a pendulum

  2. by pressing and releasing a horizontal spring

  3. by striking a guitar string

  4. by rotating a top
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If we press and release a horizontal spring, it exhibits a confined motion of compression and rarefaction. So, it shows a replica of longitudinal waves. A swinging pendulum performs simple harmonic motion. A struck guitar string exhibits a replica of transverse waves. A rotating top exhibits rotational motion.

Multiple choice physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

Sound waves in air are

  1. transverse

  2. longitudinal

  3. electromagnetic

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

Sound waves are longitudinal waves because the disturbance of the medium particles is parallel to the direction of propagation of wave. The compression and rarefraction pulses produced moves in the direction parallel to the propagation direction of wave.

Multiple choice physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

A tuning fork is excited by striking it with a padded hammer. What would be the nature of the vibrations executed by the prongs as well as the stem of the fork respectively ? (The reference direction is that of the propagation of the sound wave.)

  1. Both vibrate longitudinally

  2. Both vibrate transversely

  3. The prong vibrate longitudinally whereas the stem vibrates transversely

  4. The prong vibrate transversely whereas the stem vibrates longitudinally
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When a tuning fork is struck, the prongs vibrate transversely (perpendicular to the length of the prong). The stem, which is connected to the base of the prongs, vibrates longitudinally (along the axis of the stem) to transmit the sound to the resonance box.

Multiple choice physics propagation of sound waves sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

The ratio of the speed of a body to the speed of sound is called:

  1. Mach number

  2. Doppler Ratio

  3. Sonic index

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

Mach number of a body is the ratio of its speed to that of local sound.
The local speed of sound, and thereby the Mach number, depends on the condition of the surrounding medium, in particular the temperature and pressure. The Mach number is primarily used to determine the approximation with which a flow can be treated as an incompressible flow. 

Multiple choice physics vibrations of stretched strings sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

Which type of wave is produced in the stem of tuning fork?

  1. transverse

  2. transverse stationary

  3. longitudinal

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

When tuning fork is sounded by striking its one end on rubber pad 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. 

Multiple choice physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

Which of the following is the longitudinal wave?

  1. Sound waves

  2. Waves on plucked string

  3. Water waves

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

In sound waves vibration of particle is along the propagation of wave So it is longitudinal and in other options all are transverse wave as vibration of particle is perpendicular to the propagation of wave.  

Multiple choice physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

Consider the following statement:
(a) Sound waves are longitudinal in nature.
(b) Sound waves cannot travel through vacuum.
(c) Sound waves are produced by oscillating charged particles only.
(d) Sound waves are electromagnetic waves.
Which of the following statements are correct ?

  1. (a) and (b)

  2. (b) and (c)

  3. (a), (b) and (d)

  4. (a),(b),(c) and (d)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sound waves are longitudinal waves. It needs a medium to propagate. Sound waves are example of mechanical waves, not electromagnetic waves. Electromagnetic waves are created by the vibration of an electric charge.

Multiple choice physics study of sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

Longitudinal waves are also called

  1. Rarefactional waves

  2. Compressional waves

  3. Sound waves

  4. Light waves
Reveal answer Fill a bubble to check yourself
B Correct answer
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, 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 to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.
Longitudinal waves, also known as l-waves, are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of travel of the wave. Longitudinal waves are also called compressional waves or compression waves, because they produce compression and rarefaction when traveling through a medium.  In longitudinal waves, the displacement of the medium is parallel to the propagation of the wave.

Multiple choice physics sound sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

The musical note A is a sound wave. The note has a frequency of 440 Hz and a wavelength of 0.784 m. Calculate the speed of the musical note in m/s.

  1. 343

  2. 345

  3. 34

  4. 346
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let,

The frequency of the musical note is $\nu = 440 Hz = 440 s^{-1}$

The wavelength of the musical note is $\lambda = 0.784 m $

Now, the frequency of the musical note is 
$\nu = \dfrac{v}{\lambda}$

where, v is the speed of the musical note 
Hence, the speed of the musical note is
$v = \nu \lambda$

$v = 440 \times 0.784$

$v = 344.96 \approx 345 ms^{-1}$

Multiple choice physics vibrations of stretched strings sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

The frequency of a tuning fork is 384 Hz and velocity of sound in air is $\displaystyle 352 ms^{-1}$. How far sound has travelled when fork completes 36 vibration?

  1. 33 m

  2. 16.5 m

  3. 11 m

  4. 22 m
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\displaystyle x = v.t = v \times \dfrac{no \ of \ complete \ vibration }{frequency \ of fork}=325$ x $\displaystyle\frac{36}{384} = 33 m$

Multiple choice physics propagation of sound waves sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

The ratio $(v)$ of velocities of sound in dry air and humid air is

  1. $v<1$
  2. $v>1$
  3. $v=1$

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

Because water molecules have less mass than the average air molecules $(N _2 (28 \text{amu}),$ while water $H _2O (18 amu)).$ But It will happen if and only if the pressure is unchanged. Given that dry and humid air are both under the same pressure then we have smaller density for humid air.
And velocity of sound waves$,v,$ in a medium is given by,


$v=\sqrt{\dfrac{\gamma E}{d}}$, here $\gamma = \dfrac{C _P}{C _V}$, 

$E$ is elasticity of the medium, and $d$ is the density.

Since, density of air decreases with humidity increases. therefore velocity of sound increases in humid air.
Option "A" is correct.

Multiple choice physics vibrations of stretched strings sound as a wave of disturbance vibrations in a tuning fork vibrations in tuning fork

When the stem of a vibrating tuning fork is pressed a sounding board, then

  1. transverse vibrations are communicated through stem to the board.

  2. longitudinal vibrations are communicated through stem to the board

  3. both longitudinal and transverse vibrations are communicated through stem on the board

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the tuning fork is set into vibration, the stem of tuning fork vibrate  up and down with longitudinal vibrations hence, when the stem of a vibrating tuning fork is pressed a sounding board, then longitudinal vibrations are communicated through stem to the board.

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

The phase difference between the particle at one compression and another particle in third compression is

  1. $\pi $ radians
  2. $2\pi $ radians
  3. $3\pi $ radians
  4. $4\pi $ radians
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

phase difference between two successive compression is $2\pi $
$\therefore $ phase difference between a particle at one compression and in third compression is $2(2\pi)= 4\pi $