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When two identical loudspeakers playing the same frequency are placed equidistant from an observer, a sound of \(60\) dB is heard if the sources are in phase with each other. However, if the two speakers are out of phase, no sound is heard. If the speakers are played with a phase difference of \(90^\circ,\) the sound heard will be:
1. \(30\sqrt2\) dB
2. \((60+\sqrt2)\) dB
3. \(57\) dB
4. \(60\sqrt2\) dB

Subtopic: Ā Pressure Wave in Sound |
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The equation of vibration of a taut string, fixed at both ends, is given by; \(y=(3~\text{mm})~\text{cos}\left(\dfrac{\pi x}{10~\text{cm}}\right)~\text{sin}(800\pi~\text{s}^{-1}{t}).\) The positions of the nodes are:
1. \(x= 0~\text{cm}, 10~\text{cm}, 20~\text{cm},....\)
2. \(x= 0~\text{cm}, 20~\text{cm}, 40~\text{cm},....\)
3. \(x= 5~\text{cm}, 10~\text{cm}, 15~\text{cm},....\)
4. \(x= 5~\text{cm}, 15~\text{cm}, 25~\text{cm},....\)
Subtopic: Ā Beats |
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Sinusoidal sound waves of the same frequency travelling in air along the \(x\)-axis and the \(y\)-axis arrive in phase with each other at the origin. Their amplitudes are equal to \(A\) (each). The amplitude of the vibration at the origin is:
               
1. \(A\)
2. \(\sqrt 2A\)
3. \(2A\)
4. \((2+\sqrt2)A\)
Subtopic: Ā Wave Motion |
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The fundamental frequencies of a closed pipe and an open pipe are identical. The first overtone for the closed pipe is \(f_c\) and for the open pipe is \(f_o.\) Their ratio \(\dfrac{f_c}{f_o}\) is:
1. \(1\) 2. \(1/2\)
3. \(2/3\) 4. \(3/2\)
Subtopic: Ā Standing Waves |
Ā 70%
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The square of the speed of sound in a mono-atomic gas is proportional to:
1. its internal energy 
2. its internal energy per unit volume 
3. its internal energy per unit mass 
4. its internal energy per unit temperature  
Subtopic: Ā Speed of Sound |
Ā 58%
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A string fixed at both ends is under tension \(T.\) It has a length \(L,\) and mass \(m.\) The fundamental frequency of the vibration is: 
1. \(\dfrac{ 1}{2L} \sqrt {\dfrac{T}{m}}\)
2. \(\dfrac{1}{4 L} \sqrt{\dfrac{T}{m}}\)
3. \(\dfrac{1}{2} \sqrt{\dfrac{TL}{2m}}\)
4. \(\dfrac{1}{2} \sqrt{\dfrac{T}{m L}}\)
Subtopic: Ā Travelling Wave on String |
Ā 57%
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The first overtone of a closed pipe has a frequency \(f_c.\) A frequency that is \(2f_c\) can be excited from an open pipe of the same length but vibrating in its: 
1. \(2^{\text{nd}}\) harmonic 2. \(3^{\text{rd}}\) harmonic
3. \(6^{\text{th}}\) harmonic 4. \(12^{\text{th}}\) harmonic
Subtopic: Ā Standing Waves |
Ā 67%
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The equation of vibration of a taut string, fixed at both ends, is given by:    \(y=(4~\text{mm})~\cos\left(\dfrac{\pi x}{30~\text{cm}}\right)~\sin\Big(400\pi s^{-1}t\Big) \)
At which points is the amplitude equal to \(2\) mm?
1. \(x = \) \(10\) cm, \(20\) cm, \(30\) cm, \(40\) cm
2. \(x=\) \(10\) cm, \(15\) cm, \(30\) cm, \(45\) cm
3. \(x =\) \(10\) cm, \(20\) cm, \(40\) cm, \(80\) cm
4. \(x = \) \(10\) cm, \(20\) cm, \(40\) cm, \(50\) cm
Subtopic: Ā Standing Waves |
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A waveform given by:    \(y=3A\sin(\omega t-kx)\)
is superposed with another waveform \(y=4A\cos(\omega t-kx).\) The amplitude of the resulting waveform will be:
1. \(7A\) 2. \(A\)
3. \(3.5A\) 4. \(5A\)
Subtopic: Ā Wave Motion |
Ā 86%
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Given below are two statements:
 
Statement I: Sound waves travelling from air into water, incident obliquely, bend towards the normal.
Statement II: Sound waves travel more slowly in water than in air.
 
1. Statement I is incorrect and Statement II is correct.
2. Both Statement I and Statement II are correct.
3. Both Statement I and Statement II are incorrect.
4. Statement I is correct and Statement II is incorrect.
Subtopic: Ā Speed of Sound |
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