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What is being enter/exited?

  1. Dec 18, 2003 #1
    Enter through one, exit through two, then enter through two, exit through one.
    What is being enter/exited?
  2. jcsd
  3. Dec 18, 2003 #2
    Airport security checkpoints?
  4. Dec 18, 2003 #3
    1 and 2

    2 and 1
  5. Dec 18, 2003 #4
    A lumped element in a alternative current circuit :)
    1 and 2 are its "starts" and "ends", which are equivalent in an alternative current circuit...
  6. Dec 18, 2003 #5
    Your hands. Putting on and then taking off a T shirt.
    Oops,,, I meant to say the shirt was he thingy bieng entered then exited.

    Probably a beter thing would by the same relation on your pants considering feet?
    But let's not go there, these mofos stink!
    Last edited: Dec 18, 2003
  7. Dec 18, 2003 #6
    my answer is air. air enter in our mouth (which is one) and can exit through our nose (which has two holes [sorry for the bad terminology] and opposite as well.
  8. Dec 18, 2003 #7
    Water in a conduct with form of Y?
  9. Dec 18, 2003 #8


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    A Mach-Zender interferometer. I don't know if it is the answer you're looking for, but it fits perfectly.

  10. Dec 18, 2003 #9
    What about elevator? Enter "though" first floor, exit through "second", then vice-versa and go home... eh? :wink:
    also could be a train: enter at station A through the left door, exit at station B through right door, then from B to A in a different manner...

    however, a capacitor in AC circuit fits more...
  11. Dec 18, 2003 #10
    Any one of the 4 areas created by two non-paralell infinite lines in R^2. You can cross through either at the intersection - (through 2), or not: (through 1).
  12. Dec 18, 2003 #11
    what is A Mach-Zender interferometer?
  13. Dec 18, 2003 #12


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    In a Mach-Zehnder (I spelled it wrong initially) interferometer, a single beam of light enters, is split into two beams which travel identical pathlengths through an electro-optically active material, such as lithium niobate or gallium arsenide, then recombined. While the beams are seperate, one of them is subject to a slight perturbation. This usually takes the form of an applied electric field. The index of refraction that one beam experiences is slightly alterred, making it experience a slightly different path length. With the correct bias, you can induce a pi/2 phase shift in one arm of the interferrometer. This allows you to modulate the throughput signal from 0-100% at very high speeds (>100 GHz).

    Edit - Just wanted to add, I worked on a rib-waveguide version of this. When I read the riddle, I thought of it immediately. We made it by combining elements we already designed - a 1 to 2 splitter and a 2 to 1 combiner - one entrance two exits, two entrances one exit.

    Last edited: Dec 18, 2003
  14. Dec 18, 2003 #13
    dare i to argue that the first beam of light is different from the end product when the two seperated beam combined?
  15. Dec 18, 2003 #14


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    In the "on" state, the beam would ideally be unalterred. Besides, when a child walks into school in the morning and leaves in the afternoon, is it the same child?

    I'm sure there is a better answer. I just can't think of it because I have my MZI on the brain.

  16. Dec 18, 2003 #15
    but you said: " While the beams are seperate, one of them is subject to a slight perturbation."- therfore i assume the beam is seperated to two beams which is encouters to something that changes something in it therfore when they combine they are different from each other.
  17. Dec 18, 2003 #16
    A heart?

    Enter through one right atrium, exit through two pulmonary arteries, enter through two pulmonary veins, exit through one aorta?

    (It would work better if I could say, enter through one vena cava, but there are 2 of those.)
  18. Dec 18, 2003 #17
    don't think is the blood in the heart, since blood from the right atrium, exit throught 1 pulmonary trunk, then enter 2 pulmonary arteries.

    i was thinking about excretory system too, but too lazy.... the question is kinda ambiguous.
    Last edited: Dec 18, 2003
  19. Dec 19, 2003 #18
    Excellent brain teaser -- much better than all those ones that can be googled.

    But are you sure the answer isn't pants (Achy47's second answer)?
  20. Dec 19, 2003 #19


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    One of these days Greg is going to make up something totally wild, with no solution in mind, just to see if we can solve it anyway.

  21. Dec 19, 2003 #20
    haha the answer is pants! Achy47 had the idea but never really came out to say it! .5 points for him!
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