Oscillations and Waves (NEET Physics): Questions 76  79 of 192
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Passage
Sound from a point isotropic source spreads equally in all directions in homogeneous medium. Therefore its intensity decreases with square of distance from the source. When distance between observer and the source changes, apart from changes in intensity, the observer listens sound of pitch higher or lower than actual pitch depending upon the fact that the distance between the observer and source is decreasing or increasing respectively. An observer O is at a distance 2R from center of a circle of radius R. A point isotropic sound source S moves on the circle with uniform angular velocity . Initially observer, source and Centre of the circle are in same line.
Question number: 76 (1 of 3 Based on Passage) Show Passage
» Oscillations and Waves » Wave Motion
Question
Starting from initial moment, the source moves through an angular displacement 180°. Intensity of the sound as observed by the observer decreases by a factor of –
Choices
Choice (4)  Response  

a.  9  
b.  4  
c.  2  
d.  3 
Question number: 77 (2 of 3 Based on Passage) Show Passage
» Oscillations and Waves » Longitudinal and Transverse Waves
Question
Sound emitted by the source at two successive instants t _{1} and t _{2} has minimum and maximum observed pitch respectively, then 
Choices
Choice (4)  Response  

a. 
 
b. 
 
c. 
 
d. 

Question number: 78 (3 of 3 Based on Passage) Show Passage
» Oscillations and Waves » Wave Motion
Question
During a complete round trip of star on the circle, the observer listens a sound, whose 
Choices
Choice (4)  Response  

a.  Wavelength first increases to a maximum value then decreases to the original value  
b.  Wavelength first decreases to maximum value then increases to the original value  
c.  During the first half time wavelength increases then decreases to the original value  
d.  Question does not provide sufficient data or is vague 
Question number: 79
» Oscillations and Waves » Simple Harmonic Motion » Force
Assertion (Ꭺ)
Consider motion for a mass spring system under gravity, motion of M is not a simple harmonic motion unless Mg is negligibly small.
Reason (Ꭱ)
For simple harmonic motion acceleration must be proportional to displacement and is directed towards the mean position.
Choices
Choice (4)  Response  

a.  Both Ꭺ and Ꭱ are true but Ꭱ is NOT the correct explanation of Ꭺ  
b.  Ꭺ is true but Ꭱ is false  
c.  Ꭺ is false but Ꭱ is true  
d.  Both Ꭺ and Ꭱ are false 