Seeing Things Through Stuff
Index of Refraction
Hiding Diamonds
and
Dispersion
First Do
L11 Index of Refraction Activity
Seeing Things Through Stuff
Answers follow.
1) The Angles of
Refraction (∠R) in
glycerol are given on
the table.
Compared to water,
what is the same about
how light refracts into
glycerol or glass?
Angle of
Angle of
Angle of
Incidence Refraction Refraction
(i)
(R) in
(R) in
Water
Glycerol
70°
45
40
60°
41
36
50°
35
31
40°
29
26
30°
22
20
20°
15
13
10°
7
7
0°
0
0
All patterns for the angles of
refraction (∠R) in glycerol or
glass are the same as those in
water.
Angle of
Angle of
Angle of
Incidence Refraction Refraction
(i)
(R) in
(R) in
Water
Glycerol
70°
45
40
60°
41
36
50°
35
31
40°
29
26
30°
22
20
20°
15
13
10°
7
7
0°
0
0
They are as follows:
 When light travels from air into glycerol along the normal, it
does not bend; it travels straight through OR i = R = 0º.
 When light travels from air into glycerol, it bends toward
the normal, or the angle of refraction (∠R) is always less
than the angle of incidence ∠i .
 When light travels from air into glycerol, as the angle of
incidence (∠i) gets smaller, the angle of refraction (∠R) gets
smaller.
 The incident and refracted rays are always on the opposite
side of the normal.
2) Compared to water,
what is different
about how light
refracts from air into
glycerol or glass?
Angle of
Angle of
Angle of
Incidence Refraction Refraction
(i)
(R) in
(R) in
Water
Glycerol
70°
45
40
60°
41
36
50°
35
31
40°
29
26
30°
22
20
20°
15
13
10°
7
7
0°
0
0
For the same angle of
incidence,
the angles of refraction
(∠R) in glycerol
are smaller than
the angles of refraction
(∠R) in water.
Angle of
Angle of
Angle of
incidence Ref raction Ref raction
(i)
(R) in
(R) in
Wate r
Glyce rol
70¡
45
40
60¡
41
36
50¡
35
31
40¡
29
26
30¡
22
20
20¡
15
13
10¡
7
7
0¡
0
0
OR Light refracts more in glycerol than it
does in water.
The amount that light bends when going
into a different medium is called its
Index of Refraction.
The Index of Refraction
is a number that
indicates how much light
refracts when going into
a different medium.
The larger the number,
the more light refracts
or bends.
Material
Vacuum
Air at STP
Water at 20 C
Gly cerine
Vegetable Oil
Glasses
Sapphire
Diamond
Index of Ref raction
1.00000
1.00029
1.33
1.473
1.47
1.52-1.62
1.77
2.417
3) Light refracts (more /
the same / less) in
glycerol than it does in
water.
4) The amount that light
bends when going into a
different medium is called
its Index of Refraction.
5) Large indexes of
Refraction bend light
(more / the same / less)
than low indexes of
Refraction.
Material
Vacuum
Air at STP
Water at 20 C
Gly cerine
Vegetable Oil
Glasses
Sapphire
Diamond
Index of Ref raction
1.00000
1.00029
1.33
1.473
1.47
1.52-1.62
1.77
2.417
6) Draw the refracted rays
relative to water for semicircular containers filled
with….
a) Vegetable Oil
Material
Vacuum
Air at STP
Water at 20 C
Gly cerine
Vegetable Oil
Glasses
Sapphire
Diamond
b) Diamond
Index of Ref raction
1.00000
1.00029
1.33
1.473
1.47
1.52-1.62
1.77
2.417
c) Air
Vegetable oil has a larger Index of Refraction
than water, so light refracts or bends more than it
would going into water.
6) Draw the refracted rays
relative to water for semicircular containers filled
with….
a) Vegetable Oil
Material
Vacuum
Air at STP
Water at 20 C
Gly cerine
Vegetable Oil
Glasses
Sapphire
Diamond
b) Diamond
Index of Ref raction
1.00000
1.00029
1.33
1.473
1.47
1.52-1.62
1.77
2.417
c) Air
Diamond has a larger Index of Refraction than
vegetable oil, so light refracts even more than it
would going into vegetable oil.
6) Draw the refracted rays
relative to water for semicircular containers filled
with….
a) Vegetable Oil
Material
Vacuum
Air at STP
Water at 20 C
Gly cerine
Vegetable Oil
Glasses
Sapphire
Diamond
b) Diamond
Index of Ref raction
1.00000
1.00029
1.33
1.473
1.47
1.52-1.62
1.77
2.417
c) Air
Air has the same Index of Refraction as the air
the light is coming from, so light does not refract
at all. It is not moving into a different medium.
See-Through-Loo
Inside View
Outside View
This is a picture of a public toilet in Switzerland that is
made entirely out of one-way glass. No one can see you in
there, but when you are inside, it looks like you're sitting in
a clear glass box. http://www.snopes.com/photos/arts/toilet.asp
7) What does this have to
do with refraction?
See-Through-Loo
Inside View
Whenever light passes
from one medium to
another…… it partially
refracts and partially
reflects.
Outside View
7) What does this have to
do with refraction?
See-Through-Loo
Inside View
Whenever light passes
from one medium to
another, it partially
refracts. and partially
reflects.
Outside View
7) What does this have to
do with refraction?
See-Through-Loo
Did you notice the
reflected ray in the
activity?
Inside View
Whenever light passes
from one medium to
another, it partially
refracts and partially
reflects.
Outside View
Partial reflection /
refraction also
occurs in windows.
Part of the light
striking the window
refracts through and
part reflects back into
the room.
If there is a difference between light brightness
on either side of a window, the light from the
bright side will refract more intensely through and
reflect more intensely back into the room.
The person in the room will see a strong reflection
of themselves compared to the image refracted
from the other side.
If there is a difference between light brightness
on either side of a window, the light from the
bright side will refract more intensely through and
reflect more intensely back into the room.
The person in the room will see a strong reflection
of themselves compared to the image refracted
from the other side.
If one side of a window is dark, the light from
the bright side will refract intensely through and
reflect intensely back into the room.
The person in the room will only see a reflection
of themselves and nothing refracted from the
other side. In this case, the girl sees the boy.
The boy sees his reflection.
If one side of a window is dark, the light from
the bright side will refract intensely through and
reflect intensely back into the room.
The person in the room will only see a reflection
of themselves and nothing refracted from the
other side. In this case, the boy sees the girl.
The girl sees her reflection.
If glass is partially coated with a metal like
aluminum or silver, the partial reflection is
strengthened so that the difference in light
intensity is not as important.
This is the principle of a one-way mirror.
Check out the One-Way Mirror Shoe Box.
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.
The index of refraction or the amount that light
bends entering a particular substance also depends on
the colour of light.
Different colours refract slightly different amounts.
This causes the colours in white to separate when
refracting and is called Dispersion.
The index of refraction of diamond (~2.4) is higher
than that of glass (~1.5-1.6). Therefore, diamond
bends light more causing a greater Dispersion or
separation of colours than glass.
Glass (~1.5-1.6).
Diamond (~2.4)