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