On 8 january, Mr Lim did an experiment.
He placed a test tube inside of a boling tube.



Then he poured glycerine into it. The test tube filled up first but when the glycerin started to fill up in the boiling tube, the test tube sort of disappeared from sight. So here's the research i done about what actually happened:
We see the edges of objects because light is either reflected or refracted into our eyes. The glycerin and the test tube both have the same reflective index. This means that that the light is not refracted when it crosses the boundary between the glycerin and the glass. And because both of them are transparent, the boundary between the two test tubes cannot be seen and thus, it looks like the test tube disappears when in actual fact, it does not.

What is reflective index or index of refraction?

Well, the refractive index (or index of refraction) of a medium is a measure of how much the speed of light (or other waves such as sound waves) is reduced inside the medium.

taken from: http://en.wikipedia.org/wiki/Refractive_index

Here is a table of some common material index of refraction:

Vacuum
1.00000
Air at STP
1.00029
Ice
1.31
Water at 20 C
1.33
Acetone
1.36
Ethyl alcohol
1.36
Sugar solution(30%)
1.38
Fluorite
1.433
Fused quartz
1.46
Glycerine
1.473
Sugar solution (80%)
1.49
Typical crown glass
1.52
Crown glasses
1.52-1.62
Spectacle crown, C-1
1.523
Sodium chloride
1.54
Polystyrene
1.55-1.59
Carbon disulfide
1.63
Flint glasses
1.57-1.75
Heavy flint glass
1.65
Extra dense flint, EDF-3
1.7200
Methylene iodide
1.74
Sapphire
1.77
Rare earth flint
1.7-1.84
Lanthanum flint
1.82-1.98
Arsenic trisulfide glass
2.04
Diamond
2.417

We haven't learn refraction yet but we're gonna learn it in the next lesson. You can learn it earlier by watching this very interesting video:

and... this is a revision of reflection:


and this is reflection - again. But it is more about light sources, how light enters our eyes and etc.


Enjoy :)