1. Dispersion is the splitting of white light into its constituent colors, producing the visible light spectrum from red to violet. 2. Isaac Newton discovered dispersion using a prism and showed that white light is a combination of colors. 3. Rainbows are formed when sunlight passes through water droplets in the air after rain, with each color refracting at a different angle within the droplet.

1. Dispersion
of
Light

2. Splitting of white light into its constituent color is
called dispersion. Dispersion of visible light produces
the colors red, orange, yellow, green, blue, and violet.
Red has the longest wavelength; violet has the shortest
wavelength. This band of colors produced is called
spectrum. The name ROY G. BIV is an easy mnemonic
for remembering the order of colors in this spectrum.
Although indigo is no longer considered as a separate
color, the letter I is still retained so that there is vowel
between B and V.

3. Dispersion of light by Prism
it was Isaac Newton who first discovered that ordinary
white light is a combination of colors. Newton passed
sunlight through a triangular piece of glass called prism
that resulted in sunlight fanning out into a band of colors.
Not contented with this result, he placed a second prism
behind the first but in a reversed position and found that
the colors recombined to form white light.

5.  Light of different colors travels at different speeds in a
particular material. Hence, a particular material has
different index of refraction for each color of light. In
general, the index of refraction increases as the
wavelength decreases.
A prism disperses visible light on the basis of differences
in the indices of refraction of a material for the different
colors of light. When a beam of white light passes from
air into a glass prism then back to air, the different color
components of light bend by different amounts at the
glass-air interface.

6. Rainbow
The rainbow, nature’s spectacular display of dispersion
of light, is formed when sunlight passes through water
droplets suspended in air after a rain shower. The droplet
of water acting like a mini prism also disperses the light.
Light from the sun enters a spherical raindrop, and the
different colors are refracted at different angles, reflected
off the back of the drop, and then bent again when they
emerge from the drop.

8. It was Rene Descartes who first gave a detailed
explanation of the formation of rainbow by
mathematically tracing the path of light in a spherical
drop of water in 1637.
1. On entering a water droplet at point A, part of the light
is refracted. Violet is deviated the most, while red the
least.
2. Light upon hitting the back surface of the droplet is
reflected internally.
3. When it exists the water-air interface, it is again
refracted and dispersed.

9. Diffraction Grafting
Diffraction is the bending of light around an obstacle
and subsequent spreading of light waves into the region
behind the obstacle. The obstacle may be slit, a wire, a
hole, strands of .hair, feathers, strings or a straightedge
and likes.
The shadows upon close scrutiny are bordered by
alternating light and dark bands. Such pattern is called
diffraction grafting.
in 1650, a Jesuit priest Francesco Gramaldi first reported
diffraction of light by an obstacle.

10. In 1821, Joseph Fraunhofer developed the diffraction
grafting. A diffraction grafting is a piece of glass over
which thousands of fine parallel lines equally spaced
and very closed to one another had been scratched
usually with a diamond point.
 With your fingers barely touching each other,
look through them. You will see a diffraction
pattern.

11. Colors of an Object
 The color of an object depends on how it interacts
with light.
 The atoms making up an object are connected by
springs which can vibrate at a specific frequency
called natural frequency.

12. The Primary Colors of Light
The primary colors of light are red, blue and green.
You can verify this if you happen to sneeze before your TV
screen or computer monitor. You will see spots of red, blue
and green. It should be noted that
Red + Blue + Green = White

13. All other colors produced by mixing suitable portions
of primary colors are called secondary colors. For example,
Red + Blue = Magenta
Red + Green = Yellow
Blue + Green = Cyan
There are three aspects of color: the waves that
produce the different sensations, the eye that receives
these sensations, and the brain that interprets these
sensations. Each color light corresponds to a different
wavelength, red having the longest wavelength and violet
the shortest.

14. Our eyes can recognize only three groups of wavelength:
red, green, and blue. But our brain can recognize these
colors and their combinations. So, as far as the brain is
concerned, there are many colors.
An opaque object selectively absorbs some light and
reflects the rest. The color of an opaque object depends on
the color of light it reflects and the color of the light
source.
A transparent material absorbs one or more frequencies of
light and transmits what is not absorbed. The color of
transparent material is the color of light it transmits.

15. In the succeeding discussions, the following symbols will
be used.
W = White
R = Red
G = Green
B = Blue
M = Magenta
Y = Yellow
C = Cyan

16. Color vision involving the absence of one pigment is called
dichromacy. The absence of red, green and blue sensitive
pigments in the cones are termed as protanopia,
deuteranopia, and tritanopia, respectively.
A deficiency is one of the pigment is called anomalus
trichromacy. In anomalous trichmacy, there is a reduction in
the brightness of either red, green, or blue. Anomalous
trichoromacy where there is “red weakness” is called
protanomaly. Green weakness is otherwise called
deuteranomaly. Blue weakness is called tritanomaly.
Tritanomaly is very rare.

17. Achromatopsia literally means “no color.” People with
achromatopsia sees only black, white, and shades of
gray.
Color blindness occurs more often in males than in females.
8% of males and 1% of females are color blind. Most cases
of color blindness are inherited.

19. Care of the Eyes
Our eyes are our windows to the world. Proper eye
care is important to prevent minimize possible eye
diseases or problems. Head injury can cause color
blindness. Wearing of helmet while riding a bike or
motorcycle and protective head gears when playing hard
sports are recommended.
Avoid looking for a long time at bright-colored
because they strain the eyes. More light is reflected by
bright colors. Resulting in excessive stimulation of the eyes.
eyes.

20. Vitanim A is good for color vision and in general to
the eyes. Intake of minimum daily requirement of vitamin
A is recommended.