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 how humans hear sound human ear study of sound sound physics

The compressions and rarefactions are transmitted across the middle ear through

  1. auditory tube

  2. ear ossicles

  3. cochlea

  4. all of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The compressions and rarefactions are transmitted across the middle ear through the three ear ossicles. The vibrations produced in the ear drum are amplified.

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

The tympanum of the ear receive the sound in the form of

  1. compressions

  2. rarefaction

  3. reflection

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

The tympanum of the ear receive the sound in the form of compressions and rarefaction. These compressions and rarefaction strike the ear drum, the ear from begins to vibrate.

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

Which part of the ear vibrates when sound waves enter our ear?

  1. Ear canal

  2. Eardrum

  3. Pinna

  4. Cochlea
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ear canal is provides the path to sound to ear .

Pinna collects the sound .
Cochlea transforms the sound in neural message .
Eardrum vibrates when sound wave strikes them .

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