14.4 Color and Polarization

1. 14.4 Color and Polarization pp. 543 - 548 Mr. Richter

2. Agenda (Today and Tomorrow • Review Homework • Introduction to Color • Notes: • Color • Color and Light • Color and Pigment • Polarization

3. 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.

4. 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.

5. Color

6. 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.

7. 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.

8. 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!

9. 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!

10. Color and Light

11. 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!

12. 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

13. 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.

14. 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? • white light • blue light • magenta light • red light • 1) cyan, 2) blue, 3) blue, 4) black

15. Day 2

16. 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

17. Agenda • Warm-Up • Upcoming Schedule/Exam • Notes: • Color and Pigment • Polarization

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

19. Color and Pigment

20. 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?

21. 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.

22. 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.

23. Polarization

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

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