In this section we will build a toy called the Polariscope.
As you can see from the above photograph, the Polariscope
creates patterns of beautiful colors, somewhat like a kaleidoscope,
but by an entirely different mechanism.
In fact, the Polariscope is made mostly of transparent plastic,
and none of the fascinating colors are visible in any of the
parts out of which it is made. The colors only appear when the
toy is finally assembled, and you look through it.
Like a kaleidoscope, when you shake the Polariscope you get a
new pattern, and new colors, and the view is never the same
The parts that make up the Polariscope are shown below:
Notice that the pieces are all colorless and clear (the polarizers
are a little bit gray, and the mylar is a tiny bit purple).
The largest part is an eight inch long clear plastic rod
an inch in diameter. This type of rod (called Lucite or
Plexiglass) is available in plastics shops.
The next piece is a piece of clear plastic tubing made
of the same material as the rod. It has a one inch
inside diameter, is an inch and a quarter long, and the
walls are an eighth of an inch thick.
Next are the polarizers. These are circles cut from
Polaroid film. This can be from cheap sunglasses, or
you can get them out of old or broken LCD displays,
such as from a watch or a small video game. They can
also be ordered from scientific supply houses such as
Next comes a bunch of cut up pieces of Mylar film (from the
same plastics shop). These are cut into triangles mostly,
although you can get creative with the shapes if you like.
A piece of the plastic rod, about a third of an inch thick,
forms a plug to keep all mylar film and the polarizers
The plastics shop can cut and polish the ends of the rod and
plug for you, or you can do it yourself. The rod cuts easily
with a fine toothed saw (such as a hacksaw), and is easily
polished by successive grades of sandpaper, up to 600 grit.
After the 600 grit paper, polishing compound on a soft cloth
will make the surface transparent. The polishing compound
can be found at the plastics shop, or in any good hardware
The pieces are then assembled. The rod fits into the tube,
about a third of an inch in. Then the first polarizer is placed
into the tube on top of the rod. Next the Mylar pieces are poured
in. The second polarizer is then added, and finally the plug.
The plug should not be pressed hard against the films, since they
must be free to move about easily as you shake the Polariscope.
Using the Polariscope
To view through the Polariscope, hold the end with the polarizers
toward the light, and put your eye up to the other end.
Notice the colors change as you shake the Polariscope, or turn it
on its axis.
Also notice that the colors are reflected in the walls of the tube,
making loops and curves out of the straight edges.
How does it do that?
The Polariscope makes use of a special property of light
To understand polarization, it helps to have a little background
on electromagnetic waves, such as light, heat, radio waves, xrays,
and gamma rays.
Electromagnetic waves are generated when a charged object is moved.
The faster the charged object moves, the more energy goes into the
production of the waves, and the waves are higher in frequency.
The lowest frequency electromagnetic waves are radio waves. These
can be generated by moving electrons in wires. Infrared radiation
can be generated by the motion of molecules bouncing around as they
As a material gets hotter, the molecules (and their electrons)
move faster, and the frequency of the infrared light generated gets higher.
Visible light can be generated by moving electrons within an atom.
Gamma rays can be generated by moving charges in the nucleus of
an atom, or by destroying charged particles by colliding them with
their antimatter counterparts.
Generating electromagnetic waves
It is easy to generate low frequency radio waves using a coil of wire,
such as we find in electric motors. When we connect a coil of wire to
a battery, electrons flow from the battery into the coil of wire.
Moving electrons are what create magnetic fields. Electricity and
magnetism can be thought of as two aspects of the same thing. Moving
electrons create magnetic fields, and moving magnetic fields cause
electrons to move.
As the electrons move into the coil of wire, they create a magnetic field.
The magnetic field starts out small, and builds up as the flow of electrons
builds up. At some point the current in the wire reaches its maximum
(determined by the voltage of the battery, and the resistance of the
circuit), and the magnetic field also reaches its maximum.
If we disconnect the battery, the flow of electrons is no longer driven
by the chemical forces in the battery. The magnetic field, no longer
supported by the battery, begins to collapse. But since a collapsing
magnetic field is a moving magnetic field, it causes the electrons in
the wire to move. The electrons are pushed by the magnetic field in
the same direction that the battery used to be pushing them.
Eventually the magnetic field completely collapses, and the electrons
We know from playing with magnets that a magnetic field can affect things
at a distance. We know from playing with static electricity that charged
objects can also affect things at a distance (rub a balloon on a cat and
watch the cat fur rise as it is attracted to the balloon).
We have seen that as electrons start flowing in a wire, a magnetic field
starts building up. We have also seen that as a magnetic field collapses
it causes electrons to flow in the wire. The magnetic field and the
electric field can thus be made to oscillate back and forth. As one
collapses, it builds up the other.
Polarization of electromagnetic waves
Magnetic fields have a north and a south. Electric fields have a positive
and a negative. You can picture the two fields as the height and width
of a balloon as you push down on it with your hand.
As the height of the balloon collapses, the width of the balloon expands.
The height is like the magnetic field, and the width is like the
electric field. Notice that the two fields are always at right angles
to one another. This is important to understanding polarization.
Electromagnetic waves are oscillating magnetic and electric fields, at
right angles to one another. They move at the speed of light (light is,
after all, an electromagnetic field). Most light that we encounter is
randomly oriented with respect to the oscillating fields. Since the
fields are created by moving electrons, and the electrons could be moving
in any direction, the fields (electric and magnetic) could be at any
If something causes the electrons to all move in the same direction,
then the fields would all be oriented in one direction. We would say
the fields are polarized (they all have their north and south poles
pointing the same way).
In our wire, the electrons are all moving in the same direction, from one end
of the wire to the other. The electric and magnetic fields produced by the
moving electrons are all produced in the same orientation, and the waves
are polarized. Light from the sun or a candle is caused by electrons
moving in all different directions, so the fields are all randomly oriented.
Their light is not polarized.
The easiest way to polarize light from the sun or a candle is to reflect
it off of a flat surface at a shallow angle. Sunlight glancing off of
water into your eyes is polarized if it comes to you from a shallow enough
angle. The electric field becomes oriented up and down, and the magnetic
field is thus left and right (remember they are always at right angles to
Some materials have their atoms aligned in rows that only allow light waves
to pass through them if the electric field is perpendicular to the rows of atoms.
The electric field that is parallel to the rows of atoms is absorbed by the
electrons in the atoms, causing the atoms to vibrate and heat up.
The waves with electric fields that are not parallel
to the rows of atoms are not affected, and travel through.
Such a material is called
a polarizing filter.
Some sunglasses are made with polarizing filters in each lens. The filter
is oriented to be at 90 degrees to the light reflected off of horizontal
surfaces like the water in our previous example. These filters block the
light that was reflected at shallow angles, thus reducing the glare from
the water (or from the sloped rear window of the car ahead of you on the
street). You can see this effect more clearly by rotating the glasses
so they are up and down, and noticing that the glare is not reduced nearly
as much as it was when the glasses were on your face in their normal
Rotating the plane of polarization
Other materials can affect polarized light in a different way. If the
molecules of a transparent substance are not symetrical, they will have
more electrons on one side of the molecule than on the other. Remember
that electrons and electromagnetic waves are closely related, and they
affect one another. The lopsided molecules can rotate the plane of
polarization of the light as it passes through the material.
The amount of rotation depends on how many wavelengths of material
the light passes through. The thicker the material, the more the
light is rotated. Also, the higher the frequency of light, the more
the light is rotated (since there are more wavelengths in the same
The Mylar pieces in the Polariscope can rotate the plane of polarization
of the light.
How the Polariscope works
In the Polariscope, light enters first through the outer polarizing
filter. This polarized light then gets rotated when it passes through
the Mylar. This rotated light now tries to get through the second
polarizing filter, but since it has been rotated, it gets blocked.
But white light contains lots of colors (lots of different frequencies
of light). Different frequencies of light (different colors) are rotated
by different amounts. Some colors will thus be rotated enough to get
through the second polarizer, while other colors will be blocked.
As the light goes through different thicknesses of Mylar, it gets rotated
by different amounts. Thus different colors will be blocked by different
thicknesses of Mylar.
This is the magic of the Polariscope. Clear pieces of plastic can affect
the colors of light that are allowed to pass though the filters. We see
colors, even though there is nothing colored in the device itself.