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    • Skua@kbin.earth
      16·
      3 天前

      Messy napkin maths to explain this to myself, because it is wild to me that 41 km of anything fits in that. I will use the top picture and assume that the guy’s hand is about the same size as mine; my hands are reasonably large, so this should err on the safe side, and his hands are at a similar distance from the camera to the spool. That gives me a very approximate scale of 2 pixels per millimetre.

      Diameter of the spool case: 365 px = 183 mm = 0.183 m Radius of the main section of the case: 91 mm = 0.091 m Length of the main section of the case: 477 px = 239 mm = 0.239 m

      Volume of a cylinder = pi r r l v1 = pi * 0.091 * 0.091 * 0.239 v1 = 0.00622 m^3

      I will assume that the shaft of the spool is the same diameter as the narrow part of the case

      Diameter of the spool shaft: 55 px = 28 mm Radius of the spool shaft: 14 mm = 0.014 v2 = pi * 0.014 * 0.014 * 0.239 v2 = 0.00015 m^3

      Subtract shaft from first volume = 0.00607 m^3

      I’ll assume that the cable has the same volume, as if the case had zero-thickness walls and the cable filled the case perfectly. Since the cable has the same volume, dividing that volume by 41,000 m should give us the cross-sectional area.

      0.00607/41000 = 1.48e-7 = 0.000000148 m^2

      Square root of that to get the length and height of that cross section = 0.000345 m = 0.345 mm

      This number can effectively serve as the diameter of the cable, since it’ll have a circular cross section. And… yeah, I can find 0.25 mm diameter optical fibre easily, so the numbers check out.

      • ladicius@lemmy.world
        9·
        3 天前

        I work in telecommunication and see fiber quite regularly.

        It really is thin, and fine is a better word. In general what you see is the coating of the fiber, and that already is very fine. The fiber itself is nearly invisible even when you hold a strand between your fingers against the light.

        A single of these nearly invisible fibers can transport a GBit/s into your home. “Any sufficiently advanced technology is indistinguishable from magic” - yep, Arthur C. Clarke was right.

        • Skua@kbin.earth
          5·
          3 天前

          Funnily enough I have also worked with them, but all of mine were short lengths so I have absolutely no sense of scale for what kilometres of it looks like rolled up. Or had, I suppose, until now. I just used them to run light into awkward spots for sensors, though, so I wasn’t exactly maxxing out the potential applications

          By a neat coincidence I also play a bit of guitar, and a quarter millimetre is the diameter of the thinnest string on most of mine. For any other guitarists reading, a 10 gauge string is 0.254 mm

      • Carmakazi@lemmy.world
        2·
        3 天前

        Having a hard time imagining commercial grade optic wire a quarter of a mm think surviving things like a mildly stiff breeze against some bushes or tree branches.

        • Skua@kbin.earth
          2·
          3 天前

          I suppose unless you’re at the very end of the length of it, it can probably account for that to some degree by just letting more fibre out. This paper (which I have only skimmed, so sorry if I’ve got this wrong) seems to say that fibres even thinner than that — 0.15 mm — can handle a force equivalent to a couple of kilograms hanging off of them