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 conditions for hearing echo echo ultrasound and its applications

An echo will be heard if the minimum distance between the source of sound and the obstacle is :

[assume air to be the medium]

  1. $1\;m$
  2. $10\;m$
  3. $15\;m$
  4. $17\;m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 344 m/s at a given temperature, say at 22 $^0 C $ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s. 


Hence, the total distance covered by the sound from the point if generation to
the reflecting surface and back should be at least 

$344 \times 0.1= 34.4 m.$

Thus for hearing distinct echoes, the minimum distance pf the obstacle from 
the source of sound must be half this distance

That is, $\frac{34.4}{2}=17.2\,m \approx 17\,m$

Multiple choice physics study of sound conditions for hearing echo echo ultrasound and its applications

Bats detect the obstacle in their path by receiving the detected

  1. Infrasonic waves

  2. Ultrasonic waves

  3. Both

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

Bats can produce ultrasonic waves by flapping their wings. They can also detect these waves.these waves produced by the bats after reflection from the obstacles like building guide them to  remain away from the obstacles during night with the help of ultrasonic waves.

Multiple choice business organisation and correspondence issues of the environment international efforts for conserving biodiversity effects of pollution on environment government efforts in pollution control

Maximum permissible noise as per Noise Pollution Rules 2000 is

  1. 75 dB

  2. 65 dB

  3. 55 dB

  4. 45 dB
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Noise level are expressed on a logarithmic scale of decibels. The baseline noise levels in the community vary around 40 dB. International standards prescribe a maximum of 50 dB for day and 40 dB for night time in a residential area. Noise over 115 dB is regarded as highly avoidable. The World Health Organization (WHO) recommends an industrial noise limit of 75 dB.

Therefore, the correct answer is option A.

Multiple choice physics acoustics reverberation applications of reflection of sound multiple reflection of sound and reverberation

A rocket is moving at a speed of $220\,\,m\,\,s^{-1}$ towards a stationary target, emits a sound of frequency  $1000 Hz$. Some of the sound reaching the target gets reflected back to the rocket as echo. The frequency of the echo as detected by the rocket is
(Take velocity of sound $= 330\,\,m\,\,s^{-1}$)

  1. $3500 Hz$
  2. $4000 Hz$
  3. $5000 Hz$
  4. $3000 Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As the source (i.e rocket) is moving toward the stationary target, therefore the frequency of sound detected by the target is
$\upsilon' = \dfrac{\upsilon _0\nu}{\nu - \nu _s} = \dfrac{1000 \times 330}{330 - 220} = \dfrac{1000 \times 330}{110} = 3000 Hz$
Now the target is the source (as it is the source of echo) and the rocket's detector is the observer who intercepts the echo of frequency \acute{\upsilon}. Hence, the frequency of the echo detected by the rocket is


$\upsilon" = \dfrac{\upsilon'(\nu + \nu _O)}{\nu} = \dfrac{3000(330 + 220)}{330} = 5000 Hz $ 

Multiple choice physics study of sound reverberation applications of reflection of sound applications of ultrasound

In SONAR, we use

  1. ultrasonic waves

  2. infrasonic waves

  3. radio waves

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

Answer is A.

Sonar illustrates how a ship on the ocean utilizes the reflecting properties of ultrasound waves to determine the depth of the ocean. A ultrasound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This technique is called sonar (originally an acronym for Sound Navigation And Ranging).

Multiple choice physics study of sound reverberation applications of reflection of sound applications of ultrasound

SONAR is

  1. SOund Navigation And Ranging

  2. SOund Nullyfying And Ranging

  3. SOund Navigation with Amplitude and Ranging

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

SONAR is the best example that illustrates how a ship on the ocean utilizes the reflecting properties of sound waves to determine the depth of the ocean. A sound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This technique is called sonar (SOund Navigation And Ranging).

Multiple choice physics study of sound reverberation applications of reflection of sound applications of ultrasound

In a good auditorium the reverberation time is

  1. 0.17 V/A

  2. > 0.17 V/A

  3. < 0.17 V/A

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

The time for which sound continues to be heard (due to persistence) after the source has stopped producing the sound is called reverberation time . Sabine gave a formula for reverberation time of a good building , which is 

               $T=0.16V/A$ ,
where $V=$ volume of building in cubic metre ,
           $A=$ total absorption of building ,
hence option C is correct .

Multiple choice audible, infra and ultra sound with its application study of sound physics

A sound waves having certain frequency travels with a speed of 336 m/s and wavelength 3 cm. Calculate the frequency. Will it be audible?

  1. $1120 Hz,\ Yes$
  2. $11200 Hz,\ Yes$
  3. $11200 Hz,\ No$
  4. $1120 Hz,\ No$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The relationship between frequency, speed of sound and wavelength of a sound wave is given as 

$Frequency=\dfrac { Speed\quad of\quad sound }{ Wavelength } \quad $.

Therefore, $Frequency,\quad \nu =\dfrac { 336\quad m/s }{ 0.03\quad m } \quad $, given that the speed of sound is 336 m/s and wavelength is 3 cm, that is 0.03 m.

$Frequency\quad \nu =11200\quad Hz\quad$.

Hence, the frequency of the sound wave is 11,200 Hz which audible because the human auditory system is sensitive to frequencies from about 20 Hz to a maximum of around 20,000 Hz.

Multiple choice audible, infra and ultra sound with its application study of sound physics

Name the sounds of the frequencies given below $100Hz$.

  1. $audible$
  2. $inaudible$
  3. $unbreakable$

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

The generally accepted standard range of audible frequencies is 20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors.
Hence, 100 Hz is an audible sound.

Multiple choice audible, infra and ultra sound with its application study of sound physics

Name the sounds of the frequencies given below $1000Hz$.

  1. $audible$
  2. $inaudible$
  3. $breakable$

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

The generally accepted standard range of audible frequencies is 20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors.
Hence, 1000 Hz is an audible sound.

Multiple choice audible, infra and ultra sound with its application study of sound physics

Waves of audible frequency ranges from :

  1. $10\:Hz$ to $10,000\:Hz$
  2. $20\:Hz$ to $20,000\:Hz$
  3. $30\:Hz$ to $30,000\:Hz$

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

We have , 

               ultrasonic frequency =20,000 Hz ,
 and         infrasonic frequency =20 Hz ,
below 20Hz and above 20,000Hz we are not able to hear any sound therefore audible frequency is in between them , from 20Hz to 20000Hz , which can be heard by human ear .

Multiple choice audible, infra and ultra sound with its application study of sound physics

The minimum audible frequency for human ears is

  1. 20 Hz

  2. 100 Hz

  3. 700 Hz

  4. 1 Hz
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The generally accepted standard range of audible frequencies is 20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. Frequencies above 20,000 Hz can sometimes be sensed by young people. High frequencies are the first to be affected by hearing loss due to age and/or prolonged exposure to very loud noises.
The range of frequency within which the sound can be heard by a human being is called the audible range of frequency.