Tag: physics

Questions Related to physics

A stone is dropped from the top of a tower of $125m$ high into a pond which is at base of the tower. When will the splash be heard at the top? (Given $g = 10ms^{-1}$ and speed of sound $=340ms^{-1}.$)

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. $5s$

  2. $0.36s$

  3. $5.36s$

  4. $2s$

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Correct Option: C

When all of the audience come out of the audotirium the reverberation time became$\frac{4}{3}$ of that when packed with the audience. If all $400$ persons come out, the ratio of the absorption of the auditorium to that a person is 

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. $1600$

  2. $1200$

  3. $3000$

  4. $1000$

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Correct Option: B

The reverberation time of a hall of volume $200m^{-3}$ is $1.7s$. The reverberation time if $20$ persons having absorptions $0.4$ entered the hall, nearly is 

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. $1.5s$

  2. $1.4s$

  3. $1.3s$`

  4. $1.2s$

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Correct Option: D

A stone is dropped into a lake from a tower 500 metre high. The sound of the splash will be heard by the man approximately after

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. 11.5 seconds

  2. 21 seconds

  3. 10 seconds

  4. 14 seconds

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Correct Option: A

Fill in the blank.

___________ is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space.

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. Reverbaration

  2. Echo

  3. Response

  4. Heat

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Correct Option: A
Explanation:

A reverberation, or reverb, is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space which could include furniture and people, and air. 

The walls and ceiling of an auditorium are covered with a fibrous material to

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. Make the auditorium fire proof

  2. Absorb sound and prevent echoes

  3. Give an ethnic look to the auditorium

  4. To prevent leakage of water from the roof

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Correct Option: B
Explanation:

  We know that soft , porous and fibrous materials are good absorbers of sound , so they are used to the walls and ceiling of an auditorium to absorb the sound .

    If this is not done , sound waves after reflections (echoes) from walls and ceiling , will interfere and due to this at some places in auditorium , sound will not be heard (destructive interference) and at some places intensity of sound will be very large (constructive interference)

What will happen if the reverberation time in a big hall is too long?

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. Sound will persist for some time in the hall

  2. The reflection may become an echo.

  3. Multiple reflection may occur

  4. All the above will happen

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Correct Option: D
Explanation:

The multiple reflection of sound from the walls of a room or hall causing sound to persist for some time is called reverberation. If the hall is too long , the reflection will become an echo.

A man standing between two cliffs hears the first echo of a sound after 2 sec and the second echo 3 sec after the initial sound. If the speed of sound be $330   {m}/{sec}$ the distance between the two cliffs should be

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. 1650 m

  2. 990 m

  3. 825 m

  4. 656 m

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Correct Option: C
Explanation:

Let $d _{1}$ and $d _{2}$ be the distances of first and second cliff from man .

Echo after 2s will be heard when sound travels a distance of $2d _{1}$ , because an echo comes back to initial point after reflection .
    therefore  by ,   distance=speed$\times$time ,
         or                 $2d _{1}=330\times2=660$ ,
         or                 $d _{1}=660/2=330m$ ,
similarly Echo after 3s will be heard when sound travels a distance of $2d _{2}$ ,  
    therefore   
         or                 $2d _{2}=330\times3=990$ ,
         or                 $d _{2}=990/2=495m$ ,
as the man is in between the cliffs , therefore distance between cliffs willbe ,
             $d=d _{1}+d _{2}=330+495=825m$

(1) The reflected pulse will be in same orientation of incident pulse due to a phase change of $\pi$ radians.
(2) During reflection the wall exerts a force on string in upward direction.
For the above given two statements choose the correct option given below.

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. Only (1) is true

  2. Only (2) is true

  3. Both are true

  4. Both are wrong

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Correct Option: D
Explanation:

The pulse will be of same orientation as before after the phase change of $2\pi$ radians

During the reflection string tries to move upward but wall applies downward force to stop movement of connected end. So both the statements are wrong.

(A).  The reverberation time is dependent on the shape of the enclosure,  position of the sources and observer.
(B) The unit of absorption coefficient in S.I. system in metric is sabine

physics study of sound reverberation applications of reflection of sound multiple reflection of sound and reverberation applications of ultrasound

  1. both (A) and (B) are true

  2. both (A) and (B) are false

  3. (A) is true but (B) is false

  4. (A) is false but (B) is true

Show answer
Correct Option: B
Explanation:
The reverberation time is independent on the shape of the enclosure, position of the sources and observer.
Absorption coefficient is unitless.