1. Chapter 13 Light and Reflection
Ms. Hanan Anabusi

2. 13-4 Color and Polarization
Objectives:
Recognize how additive colors affect the color of light.
Recognize how pigments affect the color of reflected light.
Explain how linearly polarized light is formed and detected.

3. Vocabulary Primary Colors Additive primary colors
Subtractive primary colors
Pigments
polarization

4. Why do objects appear to be a certain color?
Objects are made of material.
Material is composed of atoms and molecules.
Atoms and molecules have electrons that have a natural vibrating frequency.

5. Why do objects appear to be a certain color?
Objects have different reflecting and light-absorbing properties (smooth or rough surfaces)
Objects absorb certain wavelengths from the light falling on them and reflect the rest.
Electrons will absorb the frequency of light that matches their vibration frequency.

6. Why do objects appear to be a certain color?
Light that is not absorbed is reflected to the observer.
The frequency of the reflected light determines the “color” of the object.

7. Types of Colour Theories
Subtractive Theory
The subtractive, or pigment theory deals with how white light is absorbed and reflected off of coloured surfaces.
Additive Theory
The Additive, or light theory deals with radiated and filtered light.

8. Subtractive Theory Black absorbs most light White reflects most light
Coloured Pigments absorb light and reflect only the frequency of the pigment colour.
All colours other than the pigment colours are absorbed so this is called subtractive colour theory.
The primary colours in Subtractive Theory are:
Cyan ( C )
Magenta ( M )
Yellow ( Y )
Black ( K )
Subtractive or Pigment Theory is used in printing and painting.

9. Subtractive Primary Colors
3 Primary Subtractive Colors:
CYAN
MAGENTA
YELLOW
Subtractive primary colors filter out all light when combined.
Pigments can be produced by combining subtractive colors (magenta, yellow, and cyan).

10. Additive Theory The primary colours add together to make white
Black radiates no light
White (sun) radiates all light.
The primary colours in Additive Theory are:
Red ( R )
Green ( G )
Blue ( B )
The primary colours add together to make white
Light Theory is also called Additive Theory.
Light Theory is used in Television, theater lighting, computer monitors, and video production.

11. Additive Primary Colors
White Light is a result of the combination of
3 Primary Additive Colors:
RED
GREEN
BLUE
Light of different colors can be produced by adding light consisting of the primary additive colors (red, green, and blue).

12. Additive and Subtractive Primary Colors
Look at these webpage for how the colors combine

13. Each side of triangle is complementary color of the color at opposite vertex.
Combine vertices to get color in the middle.
Combine sides to color at vertices.
Color Triangle
RED
MAGENTA
YELLOW
GREEN
CYAN
BLUE

14. Polarization of light Waves
Light is a transverse wave,
an electromagnetic wave

15. Polarization of light Waves
Light from a typical source is composed of waves that have electric fields oscillating in RANDOM directions and so this light is unpolarized.

16. Polarization of light Waves
Light can be organized into linearly polarized light by filters that allow only the horizontal or vertical waves through. This is polarized light.

17. Polarization of Light Waves
Light is polarized when its electric fields oscillate in a single plane, rather than in any direction perpendicular to the direction of propagation.

18. Polarization of light Waves
Linear polarization is the alignment of electro-magnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other.
Light can be linearly polarized through transmission.
The line along which light is polarized is called the transmission axis of that substance.

19. Polarization of Light Waves
Three methods of polarizing light
Transmission
Reflection
Scattering

20. Polarization by Transmission
The transmission axis (or polarization axis) of a filter is the line along which the light is polarized
The polarization axis is in the same direction as the polarized wave. If the filter has a vertical polarization axis, the light waves will vibrate in the vertical direction. If the filter has a horizontal polarization axis, the light waves will vibrate in the horizontal direction.
When two polarization axes are perpendicular to each other, no light can pass through. But if the polarization axes are aligned, light (about 50%) can pass through.

21. Crossed polarizers: block propagation of electromagnetic waves
Waves on a rope
Think about the waves on a rope:

22. For light: Polarizers (Polaroid films)
Same story:

23. Polarization by Reflection
Light can also become polarized when it is reflected.
When light is reflected at a certain angle from a surface, the reflected light is polarized parallel to the surface.
If the surface is parallel to the ground, the light will be horizontally polarized. If the surface is perpendicular to the ground, the light will be vertically polarized.

24. Polarization by Reflection
Light is also partially polarized after reflecting from a nonmetallic surface. At a special angle, called the polarizing angle or Brewster’s angle, the polarization is 100%.

25. Polarization by Scattering
Skylight is partially polarized due to scattering from molecules in the air. The amount of polarization depends on the angle that your line of sight makes with the sun.

26. The End

27. Animation of Polarization
The following animation shows a polarizing filter:

28. Assignments Class-work: Homework:
Section Review, page 529, odd questions.
Homework:
Section Review, page 529, even questions.
11-3 Properties of Waves