Physics · Science General

Acoustics and Sound Waves

2,160 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

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$

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

A boy shouts while standing in front of a hill. He hears an echo after 6 sec. If the speed of sound  in air is 340 m/s. What is the distance of the hill from the position of the body?

  1. 519 m

  2. 1020 m

  3. 2040 m

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

Let distance of hill from the position of the body = d
Echo is heard after 6 sec
$d = v \dfrac{t}{2}$
$= \dfrac{(340 \times 6)}{2}$
$= 1020 m$

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

A sonar echo takes 8.8 s to return from a shack. How far away is the shack?

Given speed of sound in sea-water = 1533 m/s

  1. 348 m

  2. 5720 m

  3. 6745 m

  4. 13490 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let $d$ be the distance of shack from the sonar . Therefore  distance covered by sound to come back to sonar after reflection from shack ,  $=d$ ,

given , speed of sound in sea water $v=1533m/s  ,  t=8.8s$ ,
we have , distance=speed$\times time$ ,
               $d=v\times t=1533\times8.8$ ,
or            $d=13490.4m$

Multiple choice physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

The ultrasound waves can penetrate into matter to a large extent because they have 

  1. very high speed

  2. very high frequency

  3. very high wavelength

  4. very high amplitude
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The ultrasound waves can penetrate into matter to a large extent because they have very high frequency. They have frequency greater than 20,000 Hz.
Multiple choice physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

Fill in the blank. 

Sound wave in the  ______ range are best for reflecting off of small objects.

  1. Ultrasound

  2. Infrared

  3. Acoustic

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

Ultrasound has higher frequency than the audible range sound, and thus it has shorter wavelength. Due to this short wavelength, it becomes easy for it to interact(reflect, disperse) from small objects in its path.