Transcript Document

Seeing Things Through Stuff
Invisibility
& How to Hide Diamonds
Extracted from
Survival Optics L11 Index of Refraction
Demonstration notes on last slide
See-Through-Loo
Inside View
Outside View
Inside, the “Loo” is dark so that there is little
light to refract out. Note the weak reflection
from inside.
Outside, the “Loo” is bright so there is lots of
light to reflect back and refract inside.
See-Through-Sue
H. G. Wells wrote
a science fiction
novella in 1897
called “The
Invisible Man”.
This woman is transparent
because light can pass
through her, but we can
still easily see her. Why?
What conditions would
have to be met in order
for something to be truly
invisible?.
8) Recall the refracted ray
for semi-circular container
filled with air.
Since the air in the semicircular container has the
same Index of Refraction
as the air it is coming
from……
We could imagine the semicircular container was not
there.
We can imagine it as just
an outline in air.
If light travels from
a region with one index of refraction
into
another region with the same index of refraction,
there is no refracted or reflected ray.
This is the same as saying that light travels in
straight lines. Remember Rectilinear Propagation?
We see transparent objects
because they both reflect and
refract light.
The shiny areas of this woman
are well done. That’s the
reflected light.
However, the refracted light,
the light that comes through
from behind her, should be
more distorted. The brick
mortar lines are much too
regular.
This image is virtual. It
was generated by
computer only.
It is not real.
Notice the shiny areas of reflected light near the
edge of these spheres.
The refracted light comes through from behind. The
distortion of the lines indicates these are
photographs and not virtual images.
In order to be truly invisible, an
object would have to be
transparent and have the same
index of refraction as the
surrounding medium.
This would result in no reflected or refracted light.
You can see this with Ghost Crystals.
Ghost Crystals
are made from a polyacrylamide
polymer. They are called hydrophilic because they
are “water(hydro) loving (philic) “ All this means is
that they absorb a lot of water - several hundred
times their volume of water.
After they have absorbed all the water possible,
these crystals have the same index of refraction as
water.
If they are placed in air, they can be seen because
they have a different index of refraction and will
reflect and refract light.
If they are placed in water, they become invisible
because they have the same index of refraction and
will not reflect or refract light.
Hiding Diamonds
This property is one way jewelers can check for
artificial diamonds. If placed in a solution with the
same index of refraction as real diamonds, real
diamonds become invisible. Fakes can be seen.
If you want to hide the Real Diamonds, just place
them in the solution and it just looks like a jar of
liquid.
Hiding Diamonds Demonstration
If you want to hide the Acrylic “Diamonds” you have
purchased from STAO Store, just place them in
clear container and cover with Canola cooking oil