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I Optics thought experiment

  1. Sep 2, 2016 #1
    You have a glass (or plastic) dish (like a small transparent dish). You shine light onto its flat surface. Your lab partner discovers that 55% of the light has been transmitted, 55% is reflected. What is the absorbance of the dish (not in the log scale, just as a regular %age)?
    State a hypothesis and the way you would test it.

    I was asked this today in an interview. This is what I said-

    So, clearly the answer can't be -10, right, cos that just violates energy conservation.

    So I think that the glass itself could have been in an excited state and therefore, when we shone light on it, it sort of got de-excited because of the collisions with the incoming light photons and therefore, we got more light than the total incoming light released.

    Also, the way that we would test this hypothesis is by taking the glass thing into a vacuum, in darkness and with temperatures close to 0 K and measuring any electromagnetic radiation being emitted from the same.

    We could measure that using a spectrometer sort of thing (like infrared glasses measure heat, and we can see bodies glowing).

    This is what I said during the interview. The interviewer (when he'd asked me what I liked to do, I'd said I like to sit and think, and browse the internet) then said that I should now think up 9 more solutions to this problem since that's my favourite pastime and email it to him.

    Other solutions I've thought of:

    1. Maybe there's a semi-reflective surface behind the dish, off of which the transmitted light bounced, and went back through the dish, reading as reflected light.

    2. Relativistic doppler effect could alter the intensity perceived by the glass.

    Could there be any other answers?
    Last edited: Sep 2, 2016
  2. jcsd
  3. Sep 2, 2016 #2


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    Why does the question say "dish" if only the flat part is investigated? Is the curved part not receiving any light? What exactly is measured, and how?
  4. Sep 2, 2016 #3
    That's just what I remember of how he phrased it. It doesn't really have much significance. The curved part is receiving light. I just have a laser beam that I'm shining on a small glass dish.
  5. Sep 2, 2016 #4


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    Can it focus the reflected / refracted light so you get increased intensity at the sensors?
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