What would be the power of 5 of these fire crackers? What would be the intensity

Question

What would be the power of 5 of these fire crackers? What would be the intensity, and intensity level of 5 of these fire crackers at a distance of 12 m? 8. A woman stands near two speakers. a) If the speakers are on top of one another with a frequency of 488 Hz, how far back must you move one speaker in order to hear the first loud sound and the first dead sound if the speakers are: i) in phase [0.702 loud, 0.351 dead] ii) out of phase [opposite to above] b) *if the speakers are now 2.0 m apart and the woman stands 4.0 m in front of the left hand speaker and the speakers are in phase, find the two lowest frequencies for which the woman hears i) no sound [364 Hz] ii) a loud sound [730 Hz] c) A clock shaped hollow tube has a radius of 0.248 m. If a frequency of 440 Hz is played into an opening at 12 O'clock, does a listener at 3 O'clock hear a loud sound or no sound, justify your answer. [Loud sound] d) With reference to physics concepts, explain why some old theatre seats had worse acoustics than other? [With sounds from stage bouncing off walls there were locations where crests would meet troughs, resulting in destructive interference. In other words, the path difference was a multiple of lambda/2]

Explanation / Answer

ques 8

a) frequency = 488 hz

i) lambda ( path difference ) for speakers to be in phase is = velocity of sound/frequency

lambda (for first loud sound ) i.e constructive interference = 343/488

= 0.702 m

path difference ( for first dead sound ) i.e destructive interference = lambda /2

= 0.702/2

=0.351 m

ii) for out of phase (dead sound is listened ) at

lambda = 0.702 m

and for first loud sound lambda/2 is the distance = 0.351 m

b)speaker to speaker distance = 2m

distance of woman from one speaker = 4m

distance of woman from other speaker = sqrt (2^2 + 4^2)

= 4.472 m

ii) loud sound

abs( 4 - 4.472) = n*lambda

n= 1

lambda = 0.472

frequency = speed/ lamda

= 343/0.472

= 726.69 hz

i) for no sound

frequency= 726.69/2

= 363 hz

C) listener will listen loud sound as it is hollow tube and after entering the tube sound waves will get amplified due to the the constructive interfernceby striking the walls of the tube.

d) because in old theatres in walls crests meets trough which lead to destructive interfernce in which path difference = lambda/2

hence old theatres has worse acoustics than others

  

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