Wave interference?

  • #1
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Homework Statement


A student enters Best Buy prepared to buy a pair of speakers. Before he does so, he conducts an experiment with them. He places the speakers 4.0 m apart and connects a signal generator to both speakers that produces a single and consistent tone. (constant wavelength and frequency) He then walks to a point that is 2.0 m from one speaker and2.3 m from the other. At that point he notices a quiet “spot”. If the speed of the sound in the room is known to be 350 m/s, calculate the possible frequencies being played by the speakers.


Homework Equations



PD = (n-1/2) λ

The Attempt at a Solution


f = v/(lambda) = 350/6(2n + 1) = 58.33/(2n+1) .... n belongs to integer
Sorry i have no idea what I'm doing nor do i understand the question...
Could someone please direct me to a couple of videos/helpful links that would actually help me understand what's going on here? This is for my online physics course that I'm taking, and it's hard to actually follow along through a webpage.
 

Answers and Replies

  • #2
CWatters
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Make drawing of the set up showing the distances.

Do you know what they mean by "a quiet spot" ?
 
  • #3
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I'll be honest this course is osmething I haven't touched for a while as I've been busy with my actual school. I'm rusty on this subject.

Pardon my ignorance where necessary, but I believe a quiet spot indicated that the area had a destructive interference?

Do you know of any reliable youtube channels that I can rely on?
 
  • #4
CWatters
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Pardon my ignorance where necessary, but I believe a quiet spot indicated that the area had a destructive interference?
That's correct.

Try making the drawing and work out what must happen to get destructive interference at that point. Remember that both speakers are connected to the same signal generator so both speakers produce waves with the same wavelength.

Try this youtube clip...

 
  • #5
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hi; i just wanted to thank you for the help you have given me.

That video was helpful. But I am stuck here, as i know the extra distance is .3m, and i know that they are out of phase and because of this the quiet spot is created. What i dont know is the wavelength nor the frequency. I understand that they are the same because of the signal generator, but where do I go from here? How can i find(and confirm) what the potential frequencies are?
 
  • #6
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Okay; Just to ask. Since i know it is .3m apart, can i use submultiples of this to formulate information for the wavelength?
E.g, .1 m ->

frequency = 350/.1 ->3500 Hz
 
  • #7
Nathanael
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What i dont know is the wavelength nor the frequency.
But you do know the product of them.

i know the extra distance is .3m, and i know that they are out of phase and because of this the quiet spot is created.
By what fraction of a wavelength can the waves be out of phase, in order to create a quiet spot?
 
  • #8
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1/2 of a wavelength ? So they can be out of phase.

I ended up getting 583.33 Hz as a potential frequency? I used the speed of sound in the room and divided it by .6 as that is the wavelength
 
  • #9
Nathanael
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I ended up getting 583.33 Hz as a potential frequency? I used the speed of sound in the room and divided it by .6 as that is the wavelength
Right.

1/2 of a wavelength ?
That is one possibility; are there any others?
 
  • #10
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I believe that any multiple of .5 will create a deconstructive interference?(.5, 1.5, 2.5).

Okay! I think I got it now. THank you so much for your help!
 

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