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 how humans hear sound human ear study of sound sound physics

We find it difficult to hear if we put cotton in our ears. This is because

  1. cotton damps the sound wave before reaching the ear drum

  2. cotton creates a vacuum in the ear

  3. cotton conducts the vibration to the ear drum

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

Cotton, put inside ear, damps  the vibration entering the ear. So, when the damped sound reaches the eardrum, its vibration becomes lower than original. So, we find it difficult to hear.

Multiple choice how humans hear sound human ear study of sound sound physics

A very loud sound

  1. damages the hair cells of the inner ear

  2. damages the outer ear

  3. damages the middle ear

  4. reflects back from the ear
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A very loud sound damages the hair cells of the inner ear. The hair cells die and stop sending sound signals to the brain. Once damaged, these hair cells do not grow back.

Multiple choice how humans hear sound human ear study of sound sound physics

Why can't we hear the scream of bat?

  1. Because its scream consists of infrasonic sound

  2. Because its scream consists of ultrasonic sound

  3. Because its scream consists of subsonic sound

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

Bats produce ultrasonic sound and thus humans cannot hear them. Bats emit sound in the range of $20,000$ to $100,000\ Hz$ which is beyond our audible range.

Multiple choice how humans hear sound human ear study of sound sound physics

What is conductive hearing loss?

  1. When outer or middle ear leads to problem and inefficient transfer of sound

  2. When inner ear leads to problem and inefficient transfer of sound

  3. When only middle ear leads to problem and inefficient transfer of sound

  4. When inner and middle ear leads to problem and inefficient transfer of sound
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When outer or middle ear gets damage causing insufficient transfer of sound to inner ear.

Multiple choice how humans hear sound human ear study of sound sound physics

Why do we lose hearing while yawning?

  1. Muscles around middle ear contracts

  2. Muscles around middle ear expands

  3. Muscles around inner ear contracts

  4. Muscles around inner ear expands
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Muscles around middle ear contracts while yawning. So, we are not able to hear while yawning.

Multiple choice how humans hear sound human ear study of sound sound physics

How does the sound produced by a vibrating object in a medium reach your ear?

  1. Through electron transfer

  2. Through the vibration of particles

  3. Sound waves don't need a medium

  4. Not enough data
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When an object vibrates, it vibrates the neighbouring particles of the medium. These vibrating particles then vibrate to the adjacent particles. Vibrations in an object create disturbance in the medium and consequently compressions and rarefactions.  In this way, vibrations produced by an object are transferred from one particle to another in the form of compressions and rarefactions till it reaches our ear.
Region of high pressure and high density is called compression and region of low pressure and low density in the air is called rarefaction. As the object continues to vibrate, it produces a series of successive compression and rarefaction in the air, thus, propagating sound through the air and finally reaches our ears.

Multiple choice how humans hear sound human ear study of sound sound physics

The persistence of hearing for human beings is not more than

  1. 1 s
  2. $\displaystyle \frac{1}{5}\:s$
  3. $\displaystyle \frac{1}{10}\:s$
  4. $\displaystyle \frac{1}{2}\:s$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The sensation of hearing of any sound persists in our brain for 0.1s.This is called the persistence of hearing.

so the answer is C.

Multiple choice how humans hear sound human ear study of sound sound physics

Calculate he minimum distance to hear an echo.(taking the velocity of sound in air to be $330 {ms}^{-1}$)

  1. 12.8 m

  2. 24 m

  3. 8.6 m

  4. 17.5 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

To hear an echo, sound must travel to the obstacle and back. The minimum time for human ear persistence is 0.1 seconds. Distance = (speed * time) / 2 = (330 * 0.1) / 2 = 16.5 meters. 17.5 meters is the closest provided option.

Multiple choice how humans hear sound human ear study of sound sound physics

When a sound wave enters the ear, it sets the eardrum into oscillation, which  in turn causes oscillation of 3 tiny bones in the middle ear called ossicles. This oscillation is finally transmitted to the fluid filled in inner portion of the ear termed as inner ear, the motion of the fluid disturbs hair calls within the inner ear which transmit nerve impulses to the brain with information that a sound is present. The three bones present in the middle ear are named as hammer, anvil and stirrup. Out of these the stirrup is the smallest one and this only connects the middle  ear to inner ear as shown in the figure below. The area of stirrup and its extent of connection with the inner ear limits the sensitivity of the human ear. Consider a person's eat whose moving part of the eardrum has an area of about 43 mm$^{2}$ and the area of stirrup is about 3.2 mm$^{2}$. The mass of ossicles is negligible. As a result, force  exerted by sound wave in air on eardrum and ossicles is same as the force exerted by ossicles on the inner ear. Consider a sound wave having maximum pressure fluctuation of $3\times10^{-2}$ Pa from its normal equilibrium pressure value which is wqual to $10^{5}$ Pa. Frequency of sound wave is 1200 Hz. 
Data: Velocity of sound wave in air is  332 m/s. Velocity of sound wave in fluid (present in inner ear) is 1500 m/s. Bulk modulus of air is $1.42\times10^{5}$ Pa. Bulk modulus of fluid is $2.18\times10^{9}$ Pa.


Find the pressure amplitude of given sound wave in the fluid of inner ear. 

  1. 0.03 Pa

  2. 0.04 Pa

  3. 0.3 Pa

  4. 0.4 Pa
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given :   Area of stirrup        $A _s = 3.2 mm^2     = 3.2\times 10^{-6}$ $m^2$

             
  Area of eardrum     $A = 43  mm^2  = 43 \times 10^{-6} m^2$

  Pressure amplitude at eardrum    $P _o =  3 \times 10^{-2}$  Pa

Force exerted by sound wave in air on eardrum       

$F =  P _o A = 3 \times 10^{-2} \times 43 \times 10^{-6}   = 129 \times 10^{-8}$N

According to question , force exerted on eardrum is equal to force exerted by ossicles on the inner ear.

Let pressure amplitude in the fluid of inner ear be  $p' _o$

$\therefore$    $p' _o  = \dfrac{F}{A _s}  =  \dfrac{129 \times10^{-8}}{3.2 \times 10^{-6}}   = 0.4$ Pa

Multiple choice physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

The frequency of a whistle is 200 Hz. It is approaching to stationary observer with a speed 1/3 the speed of sound. The frequency of sound as heard by the observer will be 

  1. $450 Hz$
  2. $300 Hz$
  3. $400 Hz$
  4. $425 Hz$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the Doppler effect formula for a source approaching a stationary observer: f' = f * (v / (v - vs)). Given vs = v/3, f' = 200 * (v / (v - v/3)) = 200 * (v / (2v/3)) = 200 * (3/2) = 300 Hz.

Multiple choice physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

The amplitude of vibration of the particles of air through which a sound wave of intensity $2.0 \times 10 ^ { - 6 } \mathrm { Wm } ^ { - 2 }$ and frequency $1.0 kHz$ is passing - (Density of air = 1.2 $k g m ^ { - 3 }$  and speed of sound in air = 330 $m s ^ { - 1 }$ is)

  1. $4.4 \times 10 ^ { - 8 } m$
  2. $1.6 \times 10 ^ { - 8 } m$
  3. $2.4 \times 10 ^ { - 6 } m$
  4. $1.8 \times 10 ^ { - 6 } m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The intensity of a sound wave is given by I = 2 * pi^2 * f^2 * A^2 * rho * v. Rearranging for amplitude A: A = sqrt(I / (2 * pi^2 * f^2 * rho * v)). Plugging in values: I = 2e-6, f = 1000, rho = 1.2, v = 330. A = sqrt(2e-6 / (2 * 9.87 * 1e6 * 1.2 * 330)) = 1.6e-8 m.

Multiple choice physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

The longitudinal waves travel in a coiled spring at a rate of 10 m/s. The distance between two consecutive compressions is 25cm. What is the frequency of the waves?

  1. 25Hz

  2. 10Hz

  3. 40Hz

  4. 250Hz
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Answer is C.

A sound wave has a speed that is mathematically related to the frequency and the wavelength of the wave. The mathematical relationship between speed, frequency and wavelength is given by the following equation.
Speed = Wavelength * Frequency. That is, Frequency = Speed / Wavelength.
In this case, the frequency is 140 per second and wavelength is 25 cm, that is, 0.25 m.
Therefore, Frequency = 10 / 0.25  = 40 Hz.
The frequency of the wave is 40 Hz.

Multiple choice physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

A hospital uses an ultrasonic scanner to locate tumours in a tissue. The operating frequency of the scanner is $4.2$ $MH _z$. The speed of sound  in a tissue is $1.7$ ${km/s}$. The wavelength of sound in tissue is close to

  1. $4\times 10^{-4}$ $m$
  2. $8\times 10^{-4}$ $m$
  3. $4\times 10^{-3}$ $m$
  4. $8\times 10^{-3}$ $m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given:
Frequency $(f)=4.2$ $MH _z = 4.2\times 10^{6}$ $H _z$
Speed in tissue $(v)=1.7$ ${km/s} = 1700$ ${m/s}$
$\therefore$ Wavelength $=\lambda \times f=v$
$\lambda=\cfrac{v}{f}=\cfrac{1700}{4.2\times 10^{6}}=4\times 10^{-4}$ $m$