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 laws of vibrations of stretched strings sonometer and laws of transverse vibrations vibrations of stretched strings waves physics

The length of a sonometer wire $AB$ is $110 \ cm$. The distance at which two bridges should be placed from $A$ to divide the wire into $3$ segments whose fundamental  frequencies are in the ratio of $1:2:3$ ?

  1. $30 \ cm$
  2. $60 \ cm, 30 \ cm,20 \ cm$
  3. $80\ cm$
  4. $40\ cm, 80\ cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$f _{1}:f _{2}:f _{3}=1:2:3$
$\Rightarrow \dfrac{1}{l _{1}}:\dfrac{1}{l _{2}}:\dfrac{1}{l _{3}}=1:2:3$
$\Rightarrow l _{1}:l _{2}:l _{3}=6:3:2$
$l _{1}=\left ( \dfrac{6}{2+3+6} \right )\times 110=60\ cm$
$l _{2}=\dfrac{3}{11}\times 110=30\ cm$
$l _{3}=\dfrac{2}{11}\times 110=20\ cm$

Multiple choice laws of vibrations of stretched strings sonometer and laws of transverse vibrations vibrations of stretched strings waves physics

If n$ _{1},n _{2},n _{3}$ are the three  fundamental frequencies of three segments into which a string is divided, then the original fundamental frequency '$n$' of the string is given by 

  1. $\sqrt{n}=\sqrt{n _{1}}+\sqrt{n _{2}}+\sqrt{n _{3}}$
  2. $\displaystyle \dfrac{1}{\sqrt{n}}=\dfrac{1}{\sqrt{n _{1}}}+\dfrac{1}{\sqrt{n _{2}}}+\dfrac{1}{\sqrt{n _{3}}}$
  3. $n=n _{1}+n _{2}+n _{3}$
  4. ${\dfrac{1}{n}}=\displaystyle \dfrac{1}{n _{1}}+\dfrac{1}{n _{2}}+\dfrac{1}{n _{3}}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total length of string is $l=l _{1}+l _{2}+l _{3}$
but $f\propto \dfrac{1}{l}$
$\Rightarrow \dfrac{1}{f}=\dfrac{1}{f _{1}}+\dfrac{1}{f _{2}}+\dfrac{1}{f _{3}}$

Multiple choice laws of vibrations of stretched strings sonometer and laws of transverse vibrations vibrations of stretched strings waves physics

To increase the frequency by $20\%$, the tension in the string vibrating on a Sonometer has to be increased by

  1. $44\%$
  2. $33\%$
  3. $22\%$
  4. $11\%$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

frequency increased by $20\%
$$\Rightarrow f^{'}=\dfrac{6}{5}f$
$\therefore \sqrt{T^{'}}=\dfrac{6}{5}\sqrt{T}$
$\sqrt{T^{'}}=\sqrt{\dfrac{144}{100}}T$
$\therefore$ Tension is to be increased by $44\%$

Multiple choice laws of vibrations of stretched strings sonometer and laws of transverse vibrations vibrations of stretched strings waves physics

An iron load of $2 kg$ is suspended in air from the free end of a sonometer wire of length one meter. A tuning fork of frequency $256 Hz$ is in resonance with $1/\sqrt{7}$ times the length of the sonometer wire. If the load is immersed in water, the length of the wire in meter that will be in resonance with the same tuning fork is :


(Specific gravity of iron $= 8$)

  1. $\sqrt{8}$
  2. $\sqrt{6}$
  3. $\displaystyle \dfrac{1}{\sqrt{6}}$
  4. $\displaystyle \dfrac{1}{\sqrt{8}}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$f\propto \dfrac{1}{l}\sqrt{\dfrac{T}{\mu}}$
$\Rightarrow l\propto \sqrt{T}$
$\therefore \dfrac{l _{1}}{l _{2}}=\sqrt{\dfrac{T _{1}}{T _{2}}}=\sqrt{\dfrac{8}{7}}$
$\dfrac{1}{\sqrt{7}l _{2}}=\dfrac{\sqrt{8}}{\sqrt{7}}$
$\Rightarrow l _{2}=\dfrac{1}{\sqrt{8}}$

Multiple choice physics sound time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

Which of the following statements is correct?

  1. Sound travels as waves

  2. Sound travels in straight lines

  3. Sound is a form of energy

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

Sound travels as mechanical waves. A mechanical wave is a disturbance that moves and transports energy from one place to another through a medium. In sound, the disturbance is a vibrating object. And the medium can be any series of interconnected and interactive particles. This means that sound can travel through gases, liquids and solids.

Solution A: Sound travels as waves.

Multiple choice physics world of sounds time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

Which factors determine the quality of the note ?

  1. Wavelength.

  2. Frequency

  3. Time period.

  4. Wave form.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Quality is used to describe the quality of the waveform as it appears to the listener. Therefore,  the quality of a note depends upon the waveform. 
Two notes of the same pitch and loudness, played from different instruments do not sound the same because the waveforms are different and therefore differ in quality or tone.

Multiple choice physics world of sounds time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

Shock waves are produced by objects

  1. carrying electric charges and vibrating

  2. vibrating with frequency greater than 20000Hz

  3. vibrating with very large amplitude

  4. moving with a speed greater than that of sound in the medium
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Shocks are caused by objects moving faster than the speed of sound in the medium.
(The shock tries to bring the velocity of the fluid in the medium to subsonic).

Multiple choice physics world of sounds time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

Sound waves are not transmitted to long distance because,

  1. they are absorbed by the atmosphere

  2. they have constant frequency

  3. the height of antenna required, should be very high

  4. velocity of sound waves is very less
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sound waves are not transmitted to long distance because they are absorbed by the atmosphere. 

Multiple choice physics sound time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

A sound is produced by plucking a string in a musical instrument, then

  1. the velocity of wave in the string in equal to the velocity of sound in the string.

  2. the frequency of the wave in the string in equal to the frequency of the sound produced.

  3. the wave in the string is progressive.

  4. the tension in string varies from point to point.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Frequency of the wave is the property which depends on source.

Multiple choice physics sound time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

A sound wave travels with a speed of 330 m s$^{-1}$ in air. If the wavelength of the wave is 110 cm, then frequency of the wave is _______.

  1. 100 Hz

  2. 200 Hz

  3. 300 Hz

  4. 400 Hz
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the formula v = f * lambda, where v = 330 m/s and lambda = 110 cm = 1.1 m. Thus, f = v / lambda = 330 / 1.1 = 300 Hz.

Multiple choice physics sound time period, frequency and amplitude of sound amplitude, time period and frequency of a vibration nature and characteristics of sound waves

Loudness or intensity of sound depends upon:

  1. amplitude of soundwave

  2. area of vibrating body

  3. distance from the source of sound

  4. all of above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The intensity or loudness of sound depends upon  ,

(1) Amplitude (A) of vibration of the source ,
         $I\propto A^{2}$ ,
(2) Surface area  (a) of vibrating body ,
          $I\propto a$ ,
(3) Distance (r) of listener from the source ,
            $I\propto r$ ,  
(4) Frequency (f) of the source ,
            $I\propto f$ ,
(5) Density ($\rho$) of the medium  ,
          $I\propto \rho$ , 
(6) Motion of the medium , which changes the effective speed of sound .