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 determination of speed of sound by echo problems on sound sound needs a medium

Mark the incorrect statement

  1. Sound can be produced by beating an object irrespective of whether there are vibrations or not.

  2. The sound of a tabla normally has a lower pitch than the sound of a violin.

  3. A short flute will produce sound of lower pitch than a long flute.

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

(i) False [Sound is produced from a vibrating object.]

(ii) True [The sound of a tabla normally has a lower pitch than the sound of a violin.]

(iii) True[A short flute will produce sound of lower pitch than a long flute.]

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

Why are the regions of compressions and rare fractions of sound waves formed?

  1. A sound wave undergoes diffraction behind obstacles.

  2. The reflected sound wave at a fixed end interferes with the incident wave.

  3. The longitudinal movement of air molecules produces pressure fluctuations.

  4. The speed of the sound wave changes as its travels through a medium.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Longitudinal waves are made up of compressions and rarefactions. Compression happens when molecules are forced, or pressed, together. Rarefaction is just the opposite, it occurs when molecules are given extra space and allowed to expand. So, the longitudinal movement of air molecules produces pressure fluctuations which results in compression and rarefaction.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A source emits the sound of frequency $600\ Hz$ inside water. The frequency heard in air will be equal to (velocity of sound in watere$=1500\ m/s$, velocity of sound in air$=300\ m/s$)

  1. $3000\ Hz$
  2. $120\ Hz$
  3. $600\ Hz$
  4. $6000\ Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Frequency heard in the air will also be $600\space Hz.$ Whenever, the wave travels from one medium to another medium, its speed and wavelength changes but frequency remains same.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

The phenomenon of sound propagation in air is 

  1. Isothermal process

  2. Isobaric process

  3. Adiabatic process

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

the point that there is a local change in temperature due to the compression and rarefaction half$-$ cycles of the waveform and that the these changes occur so quickly that no heat can enter or leave the cycle$,$

So$,$ it callesan adiabatic process$.$
Hence,
option $(C)$ is correct answer.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A sound wave travels from south to north, in which direction do the particles of air move?

  1. west-east

  2. south-north

  3. Up-down

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sound waves are longitudinal waves and the particles of the air move in direction of propagation sound. So if the wave will travel in south-north direction,the particles of the air also travels in south-north direction.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

Sound travels in air if

  1. particles of medium travel from one place to another

  2. there is no moisture in the atmosphere

  3. disturbance moves

  4. both particles as well as disturbance travel from one place to another.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A wave is a disturbance caused in a medium. In the case of sound, only the disturbances moves causing the surround air molecules to vibrate to and fro. The disturbance is transmitted in the form of compressions and rarefactions.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

An observer heard his echo $2.5$ seconds after he produced the sound by standing before a wall $400$ m away from him. The speed of sound in air is ____ m/s

  1. $320$
  2. $160$
  3. $330$
  4. $200$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The sound travels a total distance equal to twice the distance to the wall (there and back), which is 2 * 400 = 800 meters. The time taken is 2.5 seconds. Speed is calculated as distance divided by time, so v = 800 / 2.5 = 320 m/s.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

If d is the distance between the source of sound and reflector $t _1, t _2$ are times at which echoes are heard, the expression for determination of velocity of sound in air by echo method is :

  1. $\displaystyle \frac{2d}{t _2-t _1}$
  2. $\displaystyle \frac{2d}{t _1-t _2}$
  3. $\displaystyle \frac{4d}{t _1-t _2}$
  4. $\displaystyle \frac{2d}{t _1+t _2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The speed of the sound, distance traveled and the time taken relationship if the sound is a reflected sound, that is echo, it is given as follows.
$Speed\; of \; sound=\dfrac { 2\times Distance\; traveled\; (m) }{ Time\; taken(s) } $.
In the question it is given that distance traveled by the sound from the source to the reflector is d and the time taken to hear the echo are $t _1$ and $t _2$ seconds.
The speed of the sound wave is calculated as follows.$v=\dfrac { 2d }{ t _1-t _2 } m/s$.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

An echo returns in 30 s. What is the distance of the reflecting surface from the source? 

Given that speed of sound= 342m/s

  1. 5100 m

  2. 22.66m

  3. 5130 m

  4. 22.8 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Time taken by the wave to travel from the sound to the reflecting surface $= t = \dfrac{30}{2} = 15 m$
Speed $= 342 m/s$ 
Distance of reflecting surface from the sound $= 342 \times 15 = 5130 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A man standing in front of a large wall claps at a regular frequency of $10Hz$. He finds that the echoes coincide with his clapping. (The speed od sound in air is $330ms^{-1}.)$
(i) Time taken between successive clapping is $0.1s$.
(ii) The distance between the man and the wall, after he clapping, If he hears one more echo is $33m$.
(iii) The distance between the man and the wall, after he stops clapping, if he hears four more echoes is $66m$.

  1. Only (i) and (ii) are correct.

  2. Only (ii) and (iii) re correct.

  3. Only (i) and (iii) are correct.

  4. All (i), (ii) and (iii) are correct.
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A boy clapped his hands near a cliff and heard the echo after 4s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 346 ms$^{-1}$?

  1. 2 m

  2. 1384 m

  3. 692 m

  4. 2768 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given, Speed of sound, $v = 346 ms^{-1}$ Time taken for hearing the echo, $t = 4 s$
Distance travelled by the sound $ = v \times t = 346 m/s \times 4 s = 1384 m$
In 4 s sound has to travel twice the distance between the cliff and the person.
Hence, the distance between the cliff and the person $= 1384 m/2 = 692 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A person is in front of a fort wall.  The person can hear an echo of sound produced by him when minimum distance between person and wall is 16.75 m. The velocity of sound in air is:

  1. 330 m/s

  2. 335 m/s

  3. 337.5 m/s

  4. 345 m/s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Minimum time for echo is $0.15$
So, distance travelled for echo is $=2\times 16.75=$ speed of sound $\times$ minimum time for echo
$\Rightarrow 2\times 16.75=\vartheta _{s}\times 0.1$

$\Rightarrow \vartheta _{s}=\dfrac{2\times 16.75}{0.1}$$=335 m/s$