Electromagnetic waves interact with materials in several ways that determine the color perceived. Color arises from emission, reflection, transmission, interference, dispersion, and scattering of light waves interacting with objects. The primary colors of light are red, green and blue, which combine to make white light. The primary colors of pigment are cyan, yellow and magenta, which combine to make black. Reflection, refraction, polarization, and interference cause the wide variety of colors observed from different materials due to the interaction of light waves.

1. Electromagnetic Waves
and Color

2. Color
• Color is the
perceptual
quality of light.
• The human eye
can distinguish
almost ten
million colors.

4. Types of Materials
Transparent Translucent

5. Color comes to our eyes
from objects due to:
• Emission
• Reflection
• Transmission
• Interference
• Dispersion
• Scattering

8. Emission: the object itself is
a source of light.

9. Reflection:
certain
frequencies
are
reflected
from the
object,
others are
absorbed.

11. A particular material absorbs the
light frequency that matches the
frequency at which electrons in
the atoms of that material vibrate.

12. • The energy of the frequency
absorbed turns to heat.

13. Transmission: certain
frequencies are transmitted
through the object, others
are absorbed.

14. Scattering:
the
reradiation of
certain
frequencies of
light, striking
small,
suspended
particles.

15. Interference: constructive
and destructive
interference.

16. Dispersion:
the angular
separation of a
light wave
during
refraction.

17. Why do we see the colors of
the rainbow?

18. Why is the sky blue?

19. Why is the ocean
sometimes blue, gray or
green?

20. Primary Colors of Light
http://photographycourse.net/wp-content/uploads/2008/03/rgb_illumination-300x225.jpg

21. Primary Colors of Light:
Red, Green, Blue-combine to white

22. Secondary colors of Light:
cyan, magenta, and yellow-
also combine to white.

23. • A complementary color is formed by
subtracting a primary color from
white light.
• Every secondary color is the
complement of a primary color.

24. If a blue and yellow
flashlight strike a white
object at the same time,
what color will the object
appear?

25. If red is subtracted from
white, what color remains?

26. What color will a blue ball
appear if a red light only
strikes it and why?
=>

27. Color of light is an additive
process with respect to
frequency. Why?
• The primary colors when added
together give white light.

28. Additive Color of Light
Mixing Applications
• Movie film
• Slide projector
• Television and computer displays

29. Primary Colors of Pigment
(Cyan, Yellow, Magenta combine
to give Black color pigment)

30. Notes
• The primary colors of pigment are
the secondary colors of light and vice
versa.

31. When magenta and cyan
pigments are mixed what
color results?

32. Pigment is a subtractive
color process. Why?
• Colors are formed by absorbing
(taking away) certain frequencies
from white light.
• The absence of a reflected light
wave appears as black color.

33. PIGMENT
 colored material that absorbs certain colors and transmits or reflects light
 Pigment particle is larger than a molecule and can be seen with a
microscope
 Pigment is a finely ground inorganic compound such as titanium (IV)
oxide (white), chromium (III) oxide (green), or cadmium sulfide (yellow).
 Pigment mix to form suspensions
 Molecules in pigments and dyes absorb certain colors from white light
 A pigment that absorbs only one color from the white light is primary
pigment
 Yellow pigment absorbs blue light and reflects red and green light
 Yellow, cyan, and magenta are the primary pigments
 A pigment that absorbs two primary colors and reflects on is secondary
pigment
 The secondary pigments are red (absorbs green and blue light) green
(absorbs red and blue light) and blue (absorbs red and green light)
 The primary pigment colors are the secondary light colors, the
secondary pigment colors are the primary light colors

36. Applications: painting,
printing, etc.

37. What is Polarization?
 Light is the interaction of electric and magnetic fields travelling through space.
 The electric and magnetic vibrations of a light wave occur perpendicularly to each other.
 The electric field moves in one direction and the magnetic field in another ‘perpendicular to each
other.
 So, we have one plane occupied by an electric field, another plane of the magnetic
field perpendicular to it, and the direction of travel is perpendicular to both.
 These electric and magnetic vibrations can occur in numerous planes.
 A light wave that is vibrating in more than one plane is known as unpolarized light.
 The light emitted by the sun, by a lamp or a tube light are all unpolarized light sources.
 The direction of propagation is constant, but the planes on which the amplitude occurs are
changing.

38. a polarized wave.
 Polarized waves are light waves in which
the vibrations occur in a single plane.
 Plane polarized light consists of waves in
which the direction of vibration is the
same for all waves.
 plane polarized light vibrates on only one
plane.
 The process of transforming unpolarized
light into polarized light is known as
polarization.
 The devices like the polarizers you see are
used for the polarization of light.

41. Types of Polarization
Following are the three types of polarization depending how the electric
field is oriented:
•Linear polarization
•Circular polarization
•Elliptical polarization
Linear Polarization
In linear polarization, the electric field of light is limited to a single plane
along the direction of propagation.
Circular Polarization
There are two linear components in the electric field of light that are
perpendicular to each other such that their amplitudes are equal, but the
phase difference is π/2. The propagation of the occurring electric field will
be in a circular motion.
Elliptical Polarization
The electric field of light follows an elliptical propagation. The amplitude
and phase difference between the two linear components are not equal.

42. Methods Used in the Polarization of Light
There are a few methods used in the polarization of light:
•Polarization by Transmission
•Polarization by Reflection
•Polarization by Scattering
•Polarization by Refraction
Polarization Applications
Following are the applications of polarization:
•Polarization is used in sunglasses to reduce the glare.
•Polaroid filters are used in plastic industries for performing stress analysis
tests.
•Three-dimensional movies are produced and shown with the help of
polarization.
•Polarization is used for differentiating between transverse and longitudinal
waves.
•Infrared spectroscopy uses polarization.
•It is used in seismology to study earthquakes.
•In Chemistry, the chirality of organic compounds is tested using
polarization techniques.

43. Which type of waves cannot be polarized?
Longitudinal waves such as sound waves cannot be polarized because the
motion of the particles is in one dimension.
What is meant by the plane of polarization?
A plane in which electromagnetic waves vibrate when it is polarized so as to
vibrate in a single plane.
What is a polarizer?
A polarizer is an optical device that can convert an unpolarized light wave into
a polarized light wave by blocking all other vibrations.
What is an analyzer?
An analyzer is an optical device used to determine whether the light is plane-
polarized or not.
Who discovered the polarization of light?
The French physicist Etienne Louis Malus discovered the polarization of light.

45. REFLECTION OF WAVES

49. Examples of Objects That Reflect Light
•Mirrors.
•Eyes.
•Water Surface.
•White Paper.
•Moonlight.
•Kitchen Foil.
•Jewellery and Accessories.
•Coloured Objects.

50. DIFFUSE REFLECTION When light strikes the surface of
a (non-metallic) material it bounces off in all directions
due to multiple reflections by the microscopic
irregularities inside the material

51. Laws of reflection
Specular reflection
If the reflecting surface is very smooth, the reflection of light that
occurs is called specular or regular reflection.
The laws of reflection are as follows:
1.The incident ray, the reflected ray and the normal to the
reflection surface at the point of the incidence lie in the
same plane.
2.The angle which the incident ray makes with the normal is
equal to the angle which the reflected ray makes to the same
normal.
3.The reflected ray and the incident ray are on the opposite
sides of the normal.

52. What is refraction on light?
Refraction is the bending of light (it also happens with sound, water
and other waves) as it passes from one transparent substance into
another. This bending by refraction makes it possible for us to have
lenses, magnifying glasses, prisms and rainbows
Even our eyes depend upon this bending of light. Without refraction, we
wouldn’t be able to focus light onto our retina.

53. All angles are measured from an imaginary line drawn at 90° to
the surface of the two substances This line is drawn as a dotted
line and is called the normal.
If light enters any substance with a higher refractive index (such
as from air into glass) it slows down. The light bends towards the
normal line.
If light travels enters into a substance with a lower refractive
index (such as from water into air) it speeds up. The light
bends away from the normal line.
A higher refractive index shows that light will slow down and
change direction more as it enters the substance.

56. Refraction of light in water
When light travels from air into water, it slows down, causing it to change
direction slightly. This change of direction is called refraction. When light
enters a more dense substance (higher refractive index), it ‘bends’ more
towards the normal line.
The amount of bending depends on two things:
•Change in speed – if a substance causes the light to speed up or slow
down more, it will refract (bend) more.
•Angle of the incident ray – if the light is entering the substance at a greater
angle, the amount of refraction will also be more noticeable. On the other
hand, if the light is entering the new substance from straight on (at 90° to
the surface), the light will still slow down, but it won’t change direction..

57. Substance Refractive
index
Speed of
light in
substance
(x 1,000,000
m/s)
Angle of
refraction if
incident ray
enters
substance at
20º
Air 1.00 300 20
Water 1.33 226 14.9
Glass 1.5 200 13.2
Diamond 2.4 125
efractive index of some transparent substances

58. HOW DOES REFRACTION
OF LIGHT CAUSE A
RAINBOR TO FORM?

59. Prism
 When white light shines through a prism, each color
refracts at a slightly different angle. Violet light
refracts slightly more than red light. A prism can be
to show the seven colors of the spectrum that make up
light.
 Newton showed that each of these colors cannot be
into other colors. He also showed that they can be
recombined to make white light again.
 The explanation for the colors separating out is that
light is made of waves.
 Red light has a longer wavelength than violet light.
refractive index for red light in glass is slightly
different than for violet light.
 Violet light slows down even more than red light, so
refracted at a slightly greater angle.