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 world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

Sound is produced by a

  1. vibrating body

  2. moving body

  3. oscillating body

  4. both A and C
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Sound is produced by a vibrating body.
Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in air are called travelling longitudinal waves, which we can hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively.

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

If one puts one ears to the steel rail, the sound of a coming train can be heard even when the train cannot be seen. One can conclude from this observation that
A. Sound travels faster in steel than in air.
B. Amplitude of sound in the rail is much larger than in air.
C. Sound can travel larger distance in solids than in air.
D. Quality of sound in rail is better than in air.
The reasonable conclusion are

  1. A and C

  2. A and B

  3. B and C

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

Velocity of sound is maximum in solids and least in gases
$ V _{gas} < V _{liquid} < V _{solid} $
Intensity would also be much lower in air as $I \propto a^{2}$

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound :

  1. is more dense than air and thus has more inertia, causing the bunching up of sound

  2. waves have a speed which is dependent only upon the properties of the medium

  3. is like all waves; it is able to bend into the regions of space behind obstacles

  4. is able to reflect off fixed ends and interfere with incident waves vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

These compressions and rarefactions result because sound is able to reflect off fixed ends and interfere with incident waves vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations. Compressions are the regions of high density and rarefactions are regions of low density.

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

The speed of highly penetrating ultrasonic waves is :

  1. Lower than those of audible sound waves

  2. Higher than those of audible sound wave

  3. Much higher than those of audible sound waves

  4. Same as those of audible sound waves
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Speed of highly penetrating ultrasonic waves is greater than 20,000Hz equal to $10^7$Hz

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

Suppose a stick is struck against a frying pan in vacuum. Which of the following is/are true?

  1. the frying pan vibrate

  2. we be able to hear the sound

  3. we can hear the sound just for few minutes

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

Sounds are made by vibrations. Some vibrations are easy to see.
In this case, a stick is struck against a frying pan in vacuum. The frying pan vibrates. But this happens in vacuum. Sound waves require a medium to travel through. Outer space is a vacuum, and therefore it is not heard.
Hence, the sound created by the stick and frying pan is not heard.

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

The velocity of sound in air is not affected by change in 

  1. the moisture content of the air.

  2. the temperature of air.

  3. the atmospheric pressure.

  4. the composition of air.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The speed of sound depends on temperature. The formula relating speed of sound and temperature is as follows:

$v = 331 + 0.6 \times T$, where $T$ is temperature in absolute scale and $v$ is in $m/s$.
Humidity has little effect on the speed of sound.
Air pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out each other, leaving only the effect of temperature.
Composition of air has also almost no effect on the speed of sound.

Multiple choice physics world of sounds characteristics of sound wave time period, frequency and amplitude of sound sound waves are longitudinal waves

Consider the following
l. Waves created on the surfaces of a water pond by a vibrating source.
ll. Wave created by an oscillating electric field in air.
lll. Sound waves travelling under water. 
Which of these can be polarized

  1. l and ll

  2. ll only

  3. ll and lll

  4. l, ll, and lll
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sound waves are longitude and can not be polarized. Answer A

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

A window whose area is $2m^2$ opens on street where the street noise result in an intensity level at the window of $60db$. How much acoustic power enters the window via sound waves ? Now, if an acoustic absorber is fitted at the window? 

  1. $8\mu W$
  2. $10\mu W$
  3. $4\mu W$
  4. $2\mu W$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Intensity = 60 dB

60 = 10 log $(\frac{I}{I _{ref}})$

where $I _{ref}$ is the refrence intensity , general value of this is given by 

$I _{ref} = 10^{-12}\frac{watt}{m^2}$

$\frac{I}{10^{-12}}$ = anti log (6)

$I = 10^{-12}  \times{anti log(6)} = 10^{-12} \times{10^6} = 10^{-6}$

Power = I$\times$ area = $2 \times{10^{-6}}$ watt

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

An echo of the sound produced can be heard only if it reaches our ear after -

  1. 1 / 15th of a second

  2. 1 / 13th of a second

  3. 1 / 10th of a second

  4. 1 / 5th of a second
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An echo is the repetition of sound that results as a reflection from a surface. An echo of the sound produced can be heard only if it reaches our ear after 1 / 10th of a second. This is due to the persistence of sound.

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

In order to produce an echo, the minimum distance between the source of the sound and the reflecting body should be :

  1. 14 m

  2. 16 m

  3. 17 m

  4. 20 m
Reveal answer Fill a bubble to check yourself
C 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 sound to be 344 m/s at a given temperature, say at 22 $^0C$ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s.
 
Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344 m/s) ×0.1 s = 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance. I.e., $\frac{34.4}{2} \approx 17 \,m$

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

The minimum distance between the source of a sound and reflecting body should be 17 m for the formation of an echo. True or false

[consider the medium to be air]

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A 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 sound to be 344 m/s at a given temperature, say at 22 $^0C$ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s.
 
Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344 m/s) ×0.1 s = 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance. I.e., $\frac{34.4}{2} \approx 17 \,m$

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

The time gap between the two sounds-direct and echo depends upon:

  1. medium through which the sound travels

  2. the type of obstacle

  3. the speed of sound

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

The time gap between the two sounds-direct and echo depends upon the medium through which the sound travels. These two sounds can be heard distinctly provided the Distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him without interfering with the direct sound.