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One-way mirror ball

  1. Nov 26, 2009 #1
    i had this thought a while ago and would like to have an answer

    i don't know whether or not this exists already so i thought i'd sign up and ask a forum, this is somewhat a what if question

    if a ball like object(more a ball with many sides don't know the technical name) was made out of a one-way mirror type glass. The reflective side would be inside while the outside would be the window side. Would this object take in light and keep it inside by reflecting it on the inside and keep on collecting light.

    i just would like to know what would happen, it might be nothing but i would still like to know.

    sorry if this is in the wrong forum section
     
  2. jcsd
  3. Nov 26, 2009 #2

    mathman

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    Since we could see what is happening inside, some light must be getting out.
     
  4. Nov 26, 2009 #3

    crx

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    If you send a ray of light through the "window" than the light will be reflected for a short period of time inside the ball until its energy will be absorbed by the reflective surface, that are electrons on the surface of the silver, for example, which are vibrating with the light beam frequency, in this way reflecting back the light. These electrons will need some energy to be set in motion, some of them will transmit the energy to other atoms so in pretty short time the light will be absorbed in the mirrors material. The mirror itself will increase its temperature and will radiate infrared waves back in the surrounding medium ...and so far
     
  5. Nov 26, 2009 #4
    well since it is a mirror on the inside it should reflect most of the light and keep it inside
    so it would mostly generate heat, any guess at how much
     
  6. Nov 26, 2009 #5
    I don't think one-way mirrors exist in the manner that OP imagines.
     
  7. Nov 26, 2009 #6

    crx

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    ...definitely not more than you put in....! if this is what are you looking for ...I cant really imagine what practical use would have an mirror-ball, maybe you can have some pretty cool optical illusions
     
  8. Nov 26, 2009 #7
    well at least now i have an idea of what would happen
     
  9. Nov 26, 2009 #8

    DaveC426913

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    It is also important to point out that a mirror cannot be both perfectly reflecting on the inside and still allow light from the outside.

    So, the question is: how do you get the light in there in the first place? And once you get it in, what's to stop it from leaving the same way it entered, through whatever non-perfectly-reflecting material let it in (whether that be a partially-mirrored wall - or a non-mirrored light bulb socket already inside)?


    Exactly as many watts as you put in with your original source of light.
     
  10. Nov 26, 2009 #9

    ideasrule

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    To reiterate what other posters have said, a one-way mirror lets EXACTLY the same amount of light pass in both directions. It's not more reflective on one side than on the other; rather, it has exactly the same reflectivity in both directions. One-way mirrors for looking into rooms because one room is kept brightly lit while the other is kept dim. A lot of light passes through the mirror from the bright room to the dim room, so the mirror seems transparent from the dim room. Not a lot of light passes the other way, so somebody in the bright room would think the mirror is a normal mirror.
     
  11. Nov 26, 2009 #10

    DaveC426913

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    I am very skeptical of your claim. I am well-aware that one-way mirrors are definitely dependent on the difference in lighting from one side to the other, no arguing that. But the way you are phrasing it, it would not matter which way you installed it. If you're right, you could put it in with the mirrored side on the dimmed side and it would work exactly the same - and I just don't think that's true.

    Alas, I can found no corroboration of my suspicion.
     
    Last edited: Nov 26, 2009
  12. Nov 27, 2009 #11

    ideasrule

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    The two sides of a one-way mirror aren't perfectly symmetrical; one side has the silvering while the other side doesn't. If you install the mirror the wrong way round, it will look a bit less like a mirror on one side (because there's a pane of glass in front of the silvering) and a bit less like a window on the other side. However, reflectivity should be exactly the same on both sides.
     
  13. Nov 27, 2009 #12

    vanesch

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  14. Nov 27, 2009 #13
    i don't know the properties of one way mirrors so this gives me some insight and even though it seems like the idea(from what you guys are saying) it wouldn't be world changing or anything i would still like to mess around with it myself
    so if there was a light source in that little bathroom would people be able to see in.....if a laser was shined at that box would it reflect it like a normal mirror?

    like i said i don't know the properties so i am still curious
     
  15. Nov 28, 2009 #14

    ideasrule

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    Suppose you shine a laser into the room and 50% of the light gets in, while the other 50% is reflected. If you get into the bathroom and shine a laser outwards, exactly 50% will get out while the other 50% will get in.
     
  16. Nov 28, 2009 #15

    crx

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    i don't like mirror balls anymore......
     
  17. Nov 28, 2009 #16

    Integral

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    Dave,
    You can drop the skepticism, he is right on target. In essence all mirrors work that way, all that changes is the percent reflectance.

    This even holds true for a plain sheet of glass. At night when you look from a lit room to the outside, you see a reflection of the inside. Now step outside and look through the same window from the dark. You can easily see into the lit interior. That's why we have curtains.
     
    Last edited: Nov 28, 2009
  18. Nov 28, 2009 #17

    DrGreg

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    The principle of a one-way mirror is that from one side, say 90% is reflected and 10% passes through. From the other side, 90% is absorbed and 10% gets through. But it's the same 10% passing through in either direction.
     
  19. Nov 28, 2009 #18

    DaveC426913

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    Yes, I am very aware of how windows reflect when in a bright room and transmit when in a dim room. I'm not sugggesting any of the facts about mirrors isn't true. In fact, I know it's all quite true that they do this.

    I'm just not 100% certain that the mirror's orientation does not factor in at all.

    But if you are certain that one-way mirrors are, in fact, perfectly reversible then I'll take your word for it.
     
  20. Nov 28, 2009 #19
    Unfortunately, mirrors that will pass light in one direction more than the other violate the second law of thermodynamics

    --and, by the way, is why Hawking proposed a scheme whereby blackholes would radiate energy.
     
    Last edited: Nov 28, 2009
  21. Nov 28, 2009 #20

    DaveC426913

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    Right. I can see that. It's right there with Maxwell's Demon.

    If a mirror could preferentially pass light, then you could build a box out of it and make a light (or heat) battery, or a PPM.
     
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