14.4 Color and Polarization pp Mr. Richter

Agenda (Today and Tomorrow  Review Homework  Introduction to Color  Notes:  Color  Color and Light  Color and Pigment  Polarization

Objectives: We Will Be Able To…  Recognize how additive colors effect the color of light.  Recognize how pigments affect the color of reflected light.  Explain how linearly polarized light is formed and detected.

Warm-Up:  Leaves are green. What makes them green? That is, why do we perceive them to be green?  Discuss at your table and we will discuss as a class in a few minutes.

Color

Introduction to Color  The color of an object appears different depending on the lighting conditions.  Think about what you look like under a black light.  Or some jerk’s sunglasses.  The color of an object depends on  which wavelengths of light shine on the object, and  which wavelengths are reflected.

Color  Remember, white (visible) light is a combination or red, orange, yellow, green, blue and violet.  These colors each have different wavelengths  red = ~700 nm  violet = ~400nm  When light hits an object, some wavelengths are absorbed, and some are reflected.

Color  An object will appear to be the color of the light that it reflects.  Green leaves appear green because they absorb all wavelengths of light except green, which they reflect.  If a red light shines on a green leaf, what color will the leaf appear to be?  Black!

Color  Green objects only reflect green light.  When white light shines on green objects (white light contains green), green light is reflected  When red light shines on green objects (red light contains no green), the light is absorbed, and the object appears black.  What color does the leaf appear if green light shines on it?  Green, of course!

Color and Light

 A prism breaks up light into six (or seven) distinct colors.  These beams of light cannot be further broken up, but they can be put back together.  If we add two colors of pure light together, we can create new colors.  This is not the same as mixing pigments!

Color and Light  The three primary colors of light are red green and blue  When two of these colors combine, they create a secondary color  red + green = yellow  red + blue = magenta  blue + green = cyan

Color and Light (fun facts)  The human eye can only detect the primary colors of light: red, blue and green.  Everything else is a combination of those colors.  Visual screens like monitors and TVs only have red, blue and green pixels.  The brightness of each pixel contributes to the overall picture color.

Color and Light: Your Turn  A substance is known to reflect green and blue light.  What color would it appear to be when it is illuminated by the following colors of light? 1.white light 2.blue light 3.magenta light 4.red light  1) cyan, 2) blue, 3) blue, 4) black

Day 2

Warm-Up  If pure yellow light shines on a magenta t-shirt, what color will the t-shirt appear to an observer?  Yellow light = green + red light  Magenta = reflects red + blue  Yellow shining on magenta reflects only red light

Agenda  Warm-Up  Upcoming Schedule/Exam  Notes:  Color and Pigment  Polarization

Upcoming Schedule  Today: Finish 14.4  Tomorrow: Ch. 14 Review  Friday: Ch. 14 Test (No Quarterly Exam)  Next Week: Refraction!

Color and Pigment

 When colors of light are mixed, they are additive.  Yellow light (red + green) mixed with blue light all combine to form white light.  When colors of pigment are mixed, the result is different.  Yellow pigment mixed with cyan pigment creates green. Why?

Color and Pigment  When colors of pigment mix, they are subtractive.  Each pigment (like a paint color) only reflects certain colors of light.  The more pigments are mixed, the less light is reflected back.

Color and Pigment  The primary pigment colors are:  cyan  yellow  magenta  Just like a printer cartridge.  All other pigments are formed from combinations of these pigments.

Polarization

 Light from most sources has electric and magnetic fields that oscillate at all random angles.  Vertical, horizontal,, etc.  This light is said to be unpolarized.

Polarization  Light is polarized when the all of the electromagnetic waves are transmitted at the same angle. Everything is aligned.  The vibrations of the electric and magnetic fields are parallel to each other.

Polarization  Light can be polarized in two ways:  Transmission: a polarizer (good word!) allows only waves of a certain angle to pass through.  Kind of like a picket fence.  Reflection: most waves of light bouncing off of a surface are polarized parallel to that surface  Like glare off of glass or other shiny objects.

Polarization: Applications  Most light we see that is polarized due to reflection is horizontally polarized.  Parallel to snow covered ground, car hoods, lakes, etc.  Glasses and goggles are polarized vertically to block this glare.  Like adding a horizontal picket fence.

Wrap-Up: Did we meet our objectives?  Recognize how additive colors effect the color of light.  Recognize how pigments affect the color of reflected light.  Explain how linearly polarized light is formed.

Homework  p. 548 #1-4  p. 552 #37-39, 41  Chapter 14 Test Friday