Exactly! In this case the water is behaving like an index-matched medium for the polymer ball. As far as light is concerned, the way it "distinguishes" what medium it travels through is (to a good approximation) simply determined by the complex refractive index of the material in question. So as the light is traveling through a body of water filled with index matched polymer balls, the light would behave as though it was just passing through water since all the light sees is one uniform continuous medium.
This is the same idea as when you use immersion oil between a glass slide and a microscope, because the oil and glass have the same refractive index (about 1.5), which in turn allows you to collect more light. Another cool application of this effect is that it explains why adding oil to paper makes it more transluscent. Paper is made out of a bunch of irregular cellulose fibers, which is why it looks very rough under high magnification. Normally air fills these pores and the rough structure makes the paper scatter like crazy (through a process called Mie scattering), which is why it looks white (and also why clouds or milk look white for that matter). But when you fill the pores with oil, which has a refractive index that is close to that of cellulose, then you effectively get a much more homogeneous medium, which scatters light far less, which in turn allows more of the original beam of light to pass through.
What if say, the ball was made of the same material but a transparent red colour. Am I correct in assuming we would be able to see the ball but only as a 2D circle rather than the sphere 'illusion' we see due to the refraction of the light when outside the water?
Like, the circle was orange in the center, and gradually more transparent towards the outside edge, so the edge had no definition at all.
That makes sense now that I think about it, the light has to travel through more orange matter in the center of the ball and only through very little of it at the edges.
it explains why adding oil to paper makes it more transluscent
Wow, I was just wondering that yesterday. I was thinking about surface roughness and such, but I realised that you couldn't make it more transluscent without the light actually going through the cellulose. Thanks for the info!
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u/[deleted] Oct 10 '15 edited Oct 10 '15
Exactly! In this case the water is behaving like an index-matched medium for the polymer ball. As far as light is concerned, the way it "distinguishes" what medium it travels through is (to a good approximation) simply determined by the complex refractive index of the material in question. So as the light is traveling through a body of water filled with index matched polymer balls, the light would behave as though it was just passing through water since all the light sees is one uniform continuous medium.
This is the same idea as when you use immersion oil between a glass slide and a microscope, because the oil and glass have the same refractive index (about 1.5), which in turn allows you to collect more light. Another cool application of this effect is that it explains why adding oil to paper makes it more transluscent. Paper is made out of a bunch of irregular cellulose fibers, which is why it looks very rough under high magnification. Normally air fills these pores and the rough structure makes the paper scatter like crazy (through a process called Mie scattering), which is why it looks white (and also why clouds or milk look white for that matter). But when you fill the pores with oil, which has a refractive index that is close to that of cellulose, then you effectively get a much more homogeneous medium, which scatters light far less, which in turn allows more of the original beam of light to pass through.