| Due to the many
complexities of the different kinds of light, we will only discuss 2 types of light in
this section, namely polarized, coherent light. Each of these types has its own unique
properties and has many uses to mankind. |
Polarized
Light
Before we start, try this activity. Hold one end of a rope with your left hand and the
other end with your right hand .
Start to move your left hand up and down,
producing a wave in the rope. This type of wave is known as a vertical transverse wave due to its vibration in a
vertical plane.
Next move your left hand from side to side.
You will produce another type of wave known as the horizontal
transverse wave due to its vibration in a horizontal plane.
If you move your left hand in a diagonal
direction, you produce a third type of wave which is a combination of vertical and
horizontal transverse waves. Light works in such a manner. Once any waves are left alone
or separated, this will result in the formation of polarized light.
Polarized light
consists of waves which are vibrating in one direction only. As such, we
concludes that light is a form of transverse wave.
Rays of light from a source, such as a bulb
may often vibrate about different planes (directions). Such materials are known as
polarizing filters and only allow rays vibrating in one plane to pass through them. When
all the rays vibrate about the same plane, polarized light is formed.
Light can also be characterised by its
wavelengths, degree of coherence and its ability to interfere. This will be discussed in
greater detail later. For now, let's peep into some areas where polarized light is used.
Birefringence
Sometimes splitting of light occurs in double
refraction , which is what is known as birefringence.
How does it works ?
When light enters a medium (preferably a
crystal), it gets refracted because it is passing from one medium to another. However, the
bending of the rays takes place in a rather unusual way. Waves moving on the same
particular plane will bend differently at a varying amount than those waves bending at
right angles. Therefore , it results in 2 sets of light rays.
Thus, the dispersion of the light occurs in a
double refraction, also known as birefringence. The emerging light is then polarized.
Liquid Crystal Display
(LCD)
A liquid crystal display comprises of 2
crossed polarizing filters backed by a mirror. By theory, the filters should cease light
from entering resulting in a black display. However, this time round between the filters
are liquid crystals. When there is no power, the light rays are twisted by the crystals
through 90o. They can thus penetrate through the rear filter. They are in
turn being reflected by the mirror so a white display results. The numbers or letters on
the display are made by switching on areas of the liquid crystals. This will allow a
change so that they are no longer twisted.
Sunglasses
On a sunny day, the bright glare from the sea and other
surfaces that can reflect often makes you squaint. Sunglasses employ the mechanism of
polarizing filters to help it work. Polarizing filters are fixed at a suitable angle to
cut off the rays which induces the uncomfortable glare bu at the same time also allow
other rays to pass through. That is why sunglasses help to reduce glare.
