Acoustics Flashcards
The repetition of a sound produced by the “reflection of sound waves” from an obstructing surface, loud enough and received late enough to be perceived as distinct from the source?
Echo
The intensification and prolongation of sound produced by sympathetic vibration?
Resonance
When an object vibrates at its natural frequency, it can cause another object with the same natural frequency to vibrate as well.
Unit of loudness level?
Phon
Decibel (dB)
Sone
The volume of the sound?
A. Amplitude
B. Loudness
C. Sound intensity
D. Noise
Amplitude
The “persistence” of sound in a particular space after the original sound is produced?
Reverberation
Standing waves are produced in 10m long stretched string. If the string vibrates in 5 segments and wave velocity is 20m/s, its frequency is?
a) 2Hz
b) 4Hz
c) 5Hz
d) 10Hz
5Hz
5× ʎ/2=10
ʎ = 4 m
f = v/ʎ = 20/4 = 5
If vibrations of a string are to be increased by a factor 2, tension in the string must be made
Four times
f = 1/2π×√(T/m)
The frequency of a tuning fork is 256. It will not resonate with a fork of frequency?
a) 256
b) 512
c) 738
d) 768
738
Tuning fork of frequency 256Hz will resonate with forks of integral multiple frequencies such as 256, 768, 1024 etc.
An organ pipe closed at one end has a fundamental frequency of 1500Hz. The maximum number of overtones generated by this pipe, which a normal person can hear is?
6
maximum audible f = 20kHz
n = 20000/1500 = 13
Possible Harmonics : 1,3,5,7,9,11,13
Number Of overtones = 6 (3,5,7,9,11,13)
A tube closed at one end containing air produces a fundamental note of frequency 512Hz. If the tube is open at both ends, the fundamental frequency will be __________
1024
Statement: Sound wave cannot propagate through a vacuum but light can
Reason: Sound wave cannot be polarised but light can
a) Both statement and reason are true and the reason is the correct explanation of the statement
b) Both statement and reason are true but the reason is not the correct explanation of the statement
c) Statement is true but the reason is false
d) Both statement and reason are false
Both statement and reason are true but the reason is not the correct explanation of the statement
Sound waves, being mechanical waves, cannot travel through a vacuum. Light waves being electromagnetic waves, can travel through a vacuum.
Sound of mosquito produces high pitch than the sound of a lion.
a) True
b) False
True
What is the quantity that helps us distinguish a particular voice of a singer from the voice of many singers?
a) Timbre
b) Pitch
c) Intensity
d) Music
Timbre
Sensitivity increases with a decrease in intensity.
a) True
b) False
False
What happens if the reverberation time is too large?
a) The sound becomes inaudible
b) Echoes are produced
c) Frequency becomes high
d) The sound becomes infrasonic
Echoes are produced
What will happen when sound is focussed to a particular area?
a) Echoes are produced
b) Sound becomes inaudible
c) Interference occurs
d) Frequency of sound becomes high
Interference occurs
Sound produced from equally spaced steps in a stair case at regular intervals is due to which effect?
a) Reverberation effect
b) Noise effect
c) Absorption effect
d) Echelon effect
Echelon effect
A cinema theatre has a volume of 750m2. What should be the total absorption in the theatre if the reverberation time of 1.5seconds is to be maintained?
t = 1.5 = 0.161V/A
A = 0.165*750/1.5 = 80.5
The volume of an auditorium is 12,000m3. Its reverberation time is 1.5 seconds. If the average absorption coefficient of interior surfaces is 0.4 Sabine/m2. Find the area of interior surfaces.
3300 m2
The intensity of sound produced by roaring of a lion at a distance of 5m is 0.01W/m2. Calculate the intensity level in decibel.
I = 10log(0.01/10^-12)=100 dB
Calculate the intensity level of a plane just leaving the runway having sound intensity of about 1000W/m2.
I =10log(10^3/10^-12) = 150 dB
Frequency is used for tuning musical instruments.
a) True
b) False
False
phenomenon in tuning their musical instruments. If an instrument is sounded against a standard frequency and tuned until the beats disappear, then the instrument is in tune with the standard frequency. Therefore beats are used for tuning musical instruments.
A tuning fork produces 4 beats/s when sounded with a tuning fork of frequency 512Hz. The same tuning fork, when sounded with a another tuning fork of frequency 514Hz, produces 6 beats/s. Find the frequency of the tuning fork.
508 Hz
f = 512 +/- 4 = 508 or 516
f = 514 +/- 6 = 508 or 520
When a train, blowing its whistle, approaches him, the pitch of the whistle appears to rise and it appears to drop as the engine moves away from him. What is the effect observed here?
a) Doppler effect
b) Frequency effect
c) Beats
d) Echelon effect
Doppler effect
In which of the following is the Doppler Effect symmetric?
a) Water
b) Air
c) Liquid
d) Light
Light
Doppler effect is said to be asymmetric. However, Doppler effect in light is symmetric.
What will be the velocity of sound in a perfectly rigid rod?
a) Infinity
b) Finite
c) Zero
d) Constant
Infinity
Youngs modulus = infinity
The speed of sound in moist air is greater than that in dry air.
a) True
b) False
True
Moist air contains water vapor, which is lighter than dry air. As a result, the density of moist air is lower than that of dry air.
The sound of a bomb explosion travels faster than the sound produced by a humming bee.
a) True
b) False
The velocity of sound in a medium does not depend upon its loudness, pitch or quality.
When can sound be heard over long distances?
a) On a sunny day
b) On a humid day
c) When snowing
d) On a rainy day
On a rainy day
On a rainy day, the air contains a larger amount of water vapour. This decreases the density of air. As a result, the sound travels faster in the air and can be heard over longer distances.
A person riding on a merry-go round emits a sound wave of a certain frequency. Will the person at centre observe Doppler Effect.
The person does not experience the Doppler Effect because the source is moving perpendicular to the line joining the source and the observer.
If fundamental frequency is 50 and the next successive frequencies are 150 and 250, then it is __________
a) A pipe closed at both ends
b) A pipe closed at one end
c) An open pipe
d) A stretched string
A pipe closed at one end
For a pipe closed at one end, higher frequencies are odd multiples of the fundamental frequency.
A stone thrown into still water creates a circular wave pattern moving radially outwards. If r is the distance measured from the centre to the pattern, the amplitude of the wave varies as __________
a) r(-1/2)
b) r(-1)
c) r(-3/2)
d) r(-2)
r(-1/2)
I∝1/r
But Amplitude, A∝√I
( I = 0.5rhof^2A^2*v)
A∝1/√r
A∝r(-1/2).
siren emitting sound of frequency 800Hz is going away from a static listener with a speed of 30m/s. Frequency of the sound to be heard by the listener is (Take velocity of sound as 330m/s).
f’ = v/(v+vs)f
f’ = 330/360800
= 733.3 Hz
An observer standing by the side of a road hears the siren of an ambulance, which is moving away from him. If the actual frequency of the siren is 2000Hz, then the frequency heard by the observer will be __________
Frequency Decreases
With the propagation of a longitudinal wave through a material medium, the quantities transmitted in the propagation direction are __________
a) Energy, momentum and mass
b) Energy
c) Energy and mass
d) Energy and linear momentum
Energy
Which of the following statements is true?
a) Both light and sound waves can travel in the vacuum
b) Both light and sound waves in air are transverse
c) The sound waves in air are longitudinal while the light waves are transverse
d) Both light and sound waves in air are longitudinal
The sound waves in air are longitudinal while the light waves are transverse
The velocity of sound in any gas depends upon __________
a) Wavelength of sound only
b) Density and elasticity of gas
c) Intensity of sound waves only
d) Amplitude and frequency of sound
Density and elasticity of gas
A stretched string resonates with tuning fork of frequency 512Hz when length of the string is 0.5m. The length f the string required to vibrate resonantly with a tuning fork of frequency 256Hz would be
1 m
f ∝ 1/L
A vehicle, with a horn of frequency n is moving with a velocity of 30m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency n+n1. Then (if the sound velocity in air is 300m/s)
a) n1=0.1n
b) n1=0
c) n1=10n
d) n1=-0.1n
n1=0
As the vehicle moves in a direction perpendicular to the line joining the observer and the vehicle, the component of the velocity along this direction zero. There is no Doppler effect and the frequency of sound remains unchanged.
Lights can travel in a vacuum but not sound, because ______________
a) Speed of sound is very slow than light
b) Light waves are electromagnetic in nature
c) Sound waves are electromagnetic in nature
d) Light waves are not electromagnetic in nature
Light waves are electromagnetic in nature.
Velocity of sound in air is ___________
a) Faster in dry air than in moist air
b) Directly proportional to temperature
c) Directly proportional to pressure
d) Slower in dry air than in moist air
Directly proportional to temperature
Velocity of sound is proportional to temperature. It is independent of pressure and increases with humidity.
When sound travels from air to water, which parameter does not change?
a) Wavelength
b) Frequency
c) Velocity
d) Temperature
Frequency
The apparent frequency in Doppler’s effect does not depend upon ___________
a) Speed of the observer
b) Distance between the observer and source
c) Speed of the source
d) Frequency of the source
Distance between the observer and source
Wave has simple harmonic motion whose period is 4seconds while another wave which also possesses simple harmonic motion has its period 3sec. If both are combined, then the resultant wave will have the period equal to ___________
a) 4sec
b) 5sec
c) 12sec
d) 3sec
12seconds.
On superposition of the two waves, beats are produced.
Beat frequecny=1/T2 -1/T1 = 1/3-1/4=1/12
At what temperature, the speed of sound in the air will become double of its value at 27°C?
a) 54°C
b) 627°C
c) 327°C
d) 927°C
927°C
v∝√T
The speed of a wave in a medium is 760m/s. If 3600 waves are passing through a point in the medium in 2 min, then its wavelength is?
f = 3600/120 =30
lambda = 760/30 = 25.3
An underwater sonar source operating at a frequency of 60 kHz directs its beam towards the surface. If velocity of sound in air is 330m/s, wavelength and frequency of the waves in air are ___________
a) 5.5mm, 60 kHz
b) 5.5mm, 30 kHz
c) 5.5mm, 30 kHz
d) 5.5mm, 80 kHz
5.5mm, 60 kHz
Frequency remains same
f = 60 Hz
lambda =v/f
A wave of frequency 100Hz travels along a string towards its fixed end. When this wave travels back, after reflection, a node is formed at a distance of 10cm from the fixed end. The speed of the wave (incident and reflected) is?
a) 5m/s
b) 20m/s
c) 10m/s
d) 40m/s
Distance between two successive nodes=ʎ/2=10cm
ʎ=20cm
v=γʎ=100×20=2000=20m/s.
For beats to be produced ___________
a) Frequency of sources should be different and amplitude should be the same
b) Frequency of sources should be same and amplitude should be different
c) Frequency of sources should be same and amplitude should be different
d) Frequency of sources should be same and amplitude should be the same
Frequency of sources should be different and amplitude should be the same
Sources of sound and observer are moving towards each other, the observer will hear ___________
a) High frequency, low wavelength
b) Low frequency, low wavelength
c) High frequency, low wavelength
d) Low frequency, high wavelength
High frequency, low wavelength
Which of the following effects can be used to produce ultrasonic waves?
a) Magnetostriction effect
b) Doppler Effect
c) Magnetic effect
d) Sound effect
Magnetostriction effect
When an alternating magnetic field is applied to a ferromagnetic material, then the rod is thrown into vibrations, thereby producing ultrasonic waves at resonance. Therefore ultrasonic waves can be produced using magnetostriction effect.
It is not possible to get a constant single frequency using magnetostriction effect.
a) True
b) False
True
It is not possible to get a constant single frequency using magnetostriction method because it depends on the temperature.
Which of the following causes acoustical grating?
a) Magnetic waves
b) Electric waves
c) Magnetostriction effect
d) Ultrasonic waves
Ultrasonic waves
hen ultrasonic waves are passed through a liquid, the density varies layer by layer due to the variation in pressure and hence the liquid will act as a diffraction grating called acoustical grating.
What is the principle for measurement of the velocity of ultrasonic waves?
a) Magnetostriction effect
b) Acoustical grating
c) Doppler Effect
d) Acceleration effect
Acoustical grating
hen ultrasonic waves are passed through a liquid, due to variation in pressure, the liquid will act as diffraction grating called acoustical grating. Under this condition when a monochromatic light is passed through the acoustical grating, the light gets diffracted. By using this velocity can be determined.
What is cold welding?
a) Welding at very low temperature
b) Welding using ultrasonic waves
c) Welding under water
d) Welding at constant temperature
Welding using ultrasonic waves
What is the other name for ultrasonic flaw detector?
a) Destructive testing
b) Magnetostrictive testing
c) Non-destructive testing
d) Echo testing
Non-destructive testing
Sonograms work under the principle of Doppler Effect.
a) False
b) True
True
There is an apparent change is the frequency between the incident sound waves on the foetus and the reflected sound waves from the foetus. Therefore it works on the principle of Doppler Effect.
A quartz crystal of thickness 0.001m is vibrating at resonance. Calculate the fundamental frequency. Density of quartz = 2.650×103 kg/m3 and Young’s modulus for quartz = 7.9×1010 N/m2.
f = 1/2L Sqrt(Y/rho) =2.7299×106MHz.
An ultrasound pulse sent by a source in sea is reflected by a submerged target at a distance 597.50m and reaches the source after 0.83seconds. Find the velocity of sound in sea water.
a) 495.925m/s
b) 719.879m/s
c) 110m/s
d) 1439.75m/s
Velocity = 2d/t
Velocity = 1439.75m/s.
For an echo to be distinguished as separate, it should reach the ear _________ of a second after the direct sound.
a) One-fourth
b) One-fifth
c) One-eighth
d) One-tenth
One-tenth
Sound waves reflected at a convex surface are diminished.
a) True
b) False
False
Sound waves reflected at a concave surface are diminished while the sound waves reflected at convex surfaces are large and magnified
Reverberation time is directly proportional to ____________
a) Effective surface area
b) Lateral surface area
c) Volume of the room
d) Shape of the room
Volume of the room
In the Sabine’s expression for reverberation time t=0.16V/A, A represents __________
Total absorbing power
Rock wool comes under which of the following classifications of absorbents?
a) Porous materials
b) Resonant panels
c) Cavity resonators
d) Composite types
Porous materials
Other examples of porous materials are glass wool, wood wool,
The unit of absorption is ____________
a) Poise
b) Stoke
c) Siemens
d) Sabin
Sabin
Reverberation time is independent of the shape of the room.
a) True
b) False
True
In which of the following absorbents, absorption takes place due to the frictional losses occurring due to the to and fro movement of the air contained in the material caused by the sound waves?
a) Cavity resonators
b) Resonant panels
c) Porous materials
d) Composite types
Porous materials
Which of the following types of absorbents can absorb the sound of any frequency?
a) Resonant panels
b) Cavity resonators
c) Porous materials
d) Composite types
Cavity resonators
Hard materials used for sound insulation are good absorbers.
a) True
b) False
False
Hard materials that are used for sound insulation are poor absorbers.
However, sound absorbers are poor sound insulators.
The sound insulation of plastered solid brick masonry walls varies as __________
a) Weight per unit volume
b) Weight per unit area
c) Log of weight per unit volume
d) Log of weight per unit area
Log of weight per unit area
Felt and mineral wool are examples of ___________
a) Non-porous rigid partitions
b) Porous rigid materials
c) Non-rigid porous materials
d) Non-rigid non-porous materials
Non-rigid porous materials
These materials are not usually used for the purpose of noise reduction because the sound insulation provided by them is low as compared to the rigid materials.
In rigid homogeneous walls, the transmission loss of a one-brick wall is _________
a) 10 dB
b) 20 dB
c) 50 dB
d) 70 dB
50 dB
In cavity wall construction for soundproofing, the width of the cavity should be at least _________
a) 3 cm
b) 5 cm
c) 8 cm
d) 12 cm
5 cm
Concrete floor floating construction provides good insulation against __________ sounds.
a) Impact
b) Air-borne
c) Water-borne
d) Structural
Impact
In this type of construction, an additional floor is constructed and isolated from the already existing concrete floor.
Which of the following constructions is effective against both air-borne and structure-borne sounds?
a) Timber floor floating construction
b) Use of resilient surface material
c) Timber floor with suspended ceiling and air space
d) Concrete floor floating construction
Timber floor with suspended ceiling and air space
The word Acoustic is originally derived from a Greek word meaning _________
a) to write
b) to speak
c) to hear
d) to absorb
to hear
A _______________ is produced when part of the atmosphere is compressed suddenly.
a) Vacuum
b) Heat
c) Smog
d) Sound
Sound
A _________________ produced by sound may shatter windows and can cause damage to the Plaster of walls.
a) Wind blow
b) Sonic boom
c) Explosion
d) Lighting
Sonic boom
The defect of ___________ results in confusion with the sound created next.
a) Echoes
b) Sound foci
c) Dead spots
d) Reverberation
Reverberation
Because of high concentration of reflected sound at the Sound foci, there is a deficiency of reflected sound at some point known as __________
a) Live spots
b) Dead spots
c) Sound foci
d) Reverberation
Dead spots
The formation of ___________ takes place when the reflecting surfaces are situated at a distance greater than 17 M or so.
a) Live spots
b) Loudness
c) Echoes
d) Noise
Echoes
In case of concave reflecting interior surfaces ________ are formed where reflected sound waves meet and create a sound of larger intensity.
a) Sound foci
b) Dead spots
c) Exterior noise
d) Interior noise
Sound foci
_______________ defect is due to the lack of reflecting surfaces near the source of sound and excessive absorption of sound in the hall.
a) Exterior noise
b) Loudness
c) Interior noise
d) Echoes
Loudness
_______________ defect is due to poor sound insulation.
a) Exterior noise
b) Interior noise
c) Loudness
d) Echoes
Exterior noise
The term __________ is used to indicate a big room or a hall where sound is picked up by a microphone and it includes the radio broadcasting station, television station, etc.
a) Concert hall
b) Auditorium
c) Studio
d) Recreational hall
Studio
The basic requirements of a studio will be to have perfect soundproofing and to have variable reverberation time as per nature of sound produced in it. The acoustic design of a studio require special precaution to be undertaken for its effective working.
The adequate absorbing surfaces should be provided in the hall to control the ____________
a) Loudness
b) Noise
c) Reverberation
d) Dead spots
Reverberation
In the acoustical design of a hall or an auditorium, the angle between the side walls and the curtain line should not be more than _________ degrees.
a) 20
b) 150
c) 100
d) 180
100
For lecture halls, large volumes are beneficial for weak sounds.
a) True
b) False
False
In a studio, the noise level should be brought down to ___________
a) 5-10 dB
b) 10-15 dB
c) 20-30 dB
d) 50-60 dB
20-30 dB
The recommended volume for a public lecture hall is ___________
a) 1.5-2.5 m3 per person
b) 2.5-3.5 m3 per person
c) 3.5-4.5 m3 per person
d) 5.5-6.5 m3 per person
3.5-4.5 m3 per person
cinemas : 4.0-5.0 m3 per person musical halls : 4.0-5.5 m3 per person.
The average height for small halls should be _________
a) 3 m
b) 6 m
c) 8 m
d) 10 m
6 m
Large Halls: 7.5 m
The auditorium rear wall should be concave in shape.
a) True
b) False
False
The auditorium rear wall should not be concave in shape. It should be either flat or convex in shape.
In the acoustical design of a studio, the ratio of height, breadth and length of the studio should be _________
a) 1:3:5
b) 2:3:5
c) 1:3:7
d) 2:3:7
2:3:5
. The interior surfaces of walls in a studio should be of ________ materials.
a) Absorbent
b) Adsorbent
c) Reflective
d) Refractive
Absorbent
the outer surfaces of the walls should be of the reflective type. Provision of windows should be minimum in order to prevent the noise from outside.
Rotatable cylinders are provided in the ceiling of a studio in order to obtain variable __________
a) Amplitude
b) Frequency
c) Reverberation time
d) Intensity
Reverberation time
Which of the following is not an acoustical defect?
a) Reverberation
b) Formation of echoes
c) Absorption
d) Sound foci
Absorption
Excessive reverberation is caused due to __________
a) Sufficient absorption
b) Sufficient adsorption
c) Insufficient absorption
d) Insufficient adsorption
Insufficient absorption
The formation of echoes can take place when the reflecting surfaces are located at a distance greater than __________
a) 7 m
b) 10 m
c) 13 m
d) 17 m
17 m
Sound foci is a defect caused by _____________ interior surfaces.
a) Convex refracting
b) Concave refracting
c) Convex reflecting
d) Concave reflecting
Concave reflecting
Sound intensity is high at dead spots while it is low at sound foci.
a) True
b) False
False
Sound foci involves the concentration of sound waves at certain spots creating high sound intensity. Dead spots are the points where there is a deficiency of the reflected sound waves. Hence, sound intensity is high at sound foci and low at dead spots.
Proper shape of the hall can help in preventing the formation of echoes.
a) True
b) False
True
Colouring of sound quality is caused due to _________
a) Uncontrolled resonance
b) Controlled resonance
c) Unsuitable shape of halls
d) Vehicles
Uncontrolled resonance
Coloring of sound quality is caused due to uncontrolled resonance. Another cause of this defect is selective absorption. In order to remove this defect, wood panel absorbents are used which resonate over a wide range of frequency.
Which of the following is not a property of good acoustic materials?
a) They have a low coefficient of absorption
b) They are comparatively cheap
c) They are durable
d) They are efficient over a wide frequency range
They have a low coefficient of absorption
The absorption ratio of a surface is the ratio of ___________
a) Sound absorbed to reflected sound energy
b) Sound absorbed to incident sound energy
c) Reflected sound energy to incident sound energy
d) Incident sound energy to reflected sound energy
Sound absorbed to incident sound energy
Which of the following is not a characteristic of sound?
a) Intensity
b) Frequency
c) Speed
d) Quality
Speed
The velocity of sound in bricks is __________
a) 1450 m/sec
b) 343 m/sec
c) 3000 m/sec
d) 4300 m/sec
4300 m/sec
air - 343 m/sec.
concrete : 4000 m/sec.
The intensity of sound is proportional to __________ of amplitude.
a) Square root
b) Cube root
c) Square
d) Cube
Square
Which of the following relations between loudness and intensity is correct?
a) I ∝ log L
b) I ∝ log L2
c) L ∝ log I
d) L ∝ log I2
L ∝ log I
Which law states that the magnitude of a sensation is directly proportional to the logarithm of the physical stimulus producing it?
a) Beer-Lambert law
b) Huygens–Fresnel law
c) Lorentz law
d) Weber and Fechner’s law
Weber and Fechner’s law
The intensity of sound depends on the ear of the listener.
a) True
b) False
False
However, loudness does depend on the ear of the listener
In order to find the smallest discontinuity during UT, one should use
(a) The lowest frequency possible.
(b) The highest frequency possible.
(c) The smallest probe possible
(d) probe with smallest near zone
The highest frequency possible.
Greater depth of penetration in coarse grained material may be achieved using
(a) More sweep delay
(b) Higher frequencies
(c) Less sweep delay
(d) Lower frequencies
Lower frequencies
Longitudinal ultrasonic waves can propagate in
(a) Solids only
(b) Solids & liquids only
(c) Liquid & gases only
(d) Solid, liquid & gases
Solid, liquid & gases
Transverse ultrasonic waves can propagate in
(a) Solids only
(b) Solids & liquids only
(c) Liquid & gases only
(d) Solid, liquid & gases
Solids only
Test frequencies used in ultrasonic examination of castings w.r.t. forgings
(a) Low frequency
(b) Medium frequency
(c) High frequency
(d) No effect of frequency
Low frequency
Castings have large grain sizes .hence castings generally scatter more and hence one has to use low frequencies.
For which of these areas can the ultrasound be taken for an infant but not for an adult?
a) Cranium
b) Chest
c) Arms
d) Legs
Cranium
Bones are natural impedance providers to ultrasound and so if any organ is covered or surrounded by bones, it is not possible or very difficult to take their ultrasound.
Which of the following relations are true?
a) γ increases, penetration of sound increases, resolution decreases
b) γ increases, penetration of sound decreases, resolution decreases
c) γ increases, penetration of sound decreases, resolution increases
d) γ decreases, penetration of sound increases, resolution increases
γ increases, penetration of sound increases, resolution decreases
When the frequency (γ) of the sound waves increases, it gains more energy to overcome the impedance barrier and so is able to penetrate deeper. However, the penetration may not be uniform in all places and reflection may be uneven thus it affects the resolution of the image.
