Chapter 13 Light and Reflection Ms. Hanan Anabusi

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.

Vocabulary Primary Colors Additive primary colors Subtractive primary colors Pigments polarization

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.

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.

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.

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.

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.

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). http://www.mrmont.com/games/cmycolorsubtraction.html http://www.edumedia-sciences.com/en/a284-subtractive-color http://physci.kennesaw.edu/javamirror/jc/library/30-7/simulation.html

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.

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). http://www.mrmont.com/games/rgbcoloraddition.html http://www.edumedia-sciences.com/en/a283-colors-addition http://physci.kennesaw.edu/javamirror/jc/library/30-7/simulation.html

Additive and Subtractive Primary Colors Look at these webpage for how the colors combine http://www.mrmont.com/games/ http://www.edumedia-sciences.com/en/n73-vision-and-colors http://www.mrmont.com/games/rgbcoloraddition.html http://physci.kennesaw.edu/javamirror/jc/library/30-7/index.html http://www.mrmont.com/games/cmycolorsubtraction.html

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

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

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.

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.

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.

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.

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

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.

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

For light: Polarizers (Polaroid films) Same story:

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.

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%.

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.

The End

Animation of Polarization http://micro.magnet.fsu.edu/primer/java/polarizedlight/filters/index.html The following animation shows a polarizing filter: http://www.colorado.edu/physics/2000/applets/polarized.html

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