CHAPTER 4 Light

1. CHAPTER 4Light

2. Look carefully at the cups. What is the main difference among them?

3. Light and Color • Transparent materials • Transmit most of the light that strikes it • See clearly through • Translucent Materials • Scatters light as it passes through • Can see through it w/ fuzzy/blurred details • Opaque Materials • Reflects or absorbs all of the light that strikes it • Light can’t pass through it

4. Transparent

5. Translucent

6. Opaque

7. If you know how light interacts with objects… • You can explain why objects have different colors

8. The color of any object… • Depends on the material of object and color of light striking it.

9. Rememeber: Wavelength:

10. Although light from the sun appears colorless or "white" it actually contains a range of colors similar to a rainbow. You can see these colors using a prism to separate them out.

11. Color of opaque objects • They are the color of the light they reflect. A green object such as a leaf reflects only those wavelengths that create the visual effect of green. Other colors in the light are absorbed by the leaf. White objects reflect most of the wavelengths of light that strike them. When all of these wavelengths are combined, we see white. On the other hand, when all of them are absorbed, and none reflected, we see black.

12. Color of transparent and translucent objects • Only certain colors of light can pass through • The color of a transparent or translucent object is the color of the light it transmits • Color filters • Piece of glass or plastic that allows light of only a certain color to pass through it • Ex: Red color filter only lets red light pass through • Ex: sunglasses –objects appear to change color

13. Copy these questions into your notebook! • Read pg 110 and 111 and answer: • What are the primary colors of light? • What are 2 ways to make white light? • How do you make different colors of light? • What are the secondary colors of light? • What are complementary colors? • Answer question in figure 5. • What is a pigment? • How is mixing pigments of various colors different than mixing light of various colors? • What are the primary colors of pigments? • What are the secondary colors of pigments? • Then, do section 1 assessment. You may work with partner.

14. DO NOW: • What are the primary colors (in paint)? • How are they different from the primary colors of light?

16. Combining Colors • PRIMARY COLORS • 3 colors that can combine to make ANY other color • RED, BLUE, GREEN • SECONDARY COLORS • 2 primary colors mixed together • YELLOW, MAGENTA, CYAN

19. Primary + secondary color = WHITE light

20. Complementary colors • Any two colors that combine to form white light • ex: • Yellow and blue, • cyan and red, • Magenta and green

21. How does a color TV work? • It uses only the primary colors of light (R, G, B) in different ratios/brightness to form all of the colors.

22. Mixing Pigments • What is a pigment?

23. Pigment = colored substances used to color other materials –found in ink, paints, dyes • They absorb some colors and reflect others • Whatever color a pigment reflects in the color that you see!

24. What are the Primary colors of PIGMENTS? Magenta, Cyan, Yellow

25. What happens when you keep adding pigments together? • Fewer colors of light get reflected, so we see the mixture getting darker and darker

26. Section 2 – Reflection and Mirrors

27. Representing Light waves • You can represent light waves as straight lines called RAYS.

28. What does “diffuse” mean? • Ex: • John and Jack were in an argument about who’s a better team—the Cubs or the White Sox. They started getting very angry at each other, and other students started getting involved…. so Mrs. P had to come in and diffuse the fight.

29. Regular Reflection vs. Diffuse Reflection • Regular Reflection • Smooth surface, rays refelect all at the same angle • Diffuse Reflection • Rough surface, rays reflect at different angles

30. How does your reflection wink? • On a clean sheet of paper: • St. Cassian heading • Title: How does your reflection wink? • Procedure: Answer the two questions within the procedure using COMPLETE sentences—restating the question. • Observing: Answer the questions in complete sentences, restating the question.

31. PLANE MIRRORS • = an everyday mirror • A flat sheet of glass that has a smooth silver colored coating on one side (normally the back) • Creates a regular reflection and clear image! Image = copy of an object formed by reflected or refracted rays of light

32. DO NOW • What does virtual mean?

33. Kind of Image in a Plane Mirror • You see a virtual image. = an upright image that forms where light seems to come from. The image is the same size as the object, and it is reversed. • Your image appears to be behind the mirror, but you cannot reach behind the mirror and touch it

34. Even though the light rays are reflected, your brain treats them as if they had come from behind the mirror When one looks into a mirror it appears as if you are looking through it and seeing the object on the other side.

35. Concave Mirrors • Parallel rays of light reflect so that they meet at a point. • Focal point = point at which rays parallel to the optical axis meet.

36. Representing How images form • Use a ray diagram to see where focused image forms. • See figure 10

37. Determining the Type of Image • Concave mirrors can form either virtual images or real images • Virtual Image • If object is between mirror and focal point • Appears behind the mirror and is upright • Always larger than object • Real Image • When rays actually meet • It is upside down • Might be larger or smaller than object • Occurs when object is farther away from mirror than the focal point

38. Convex Mirrors • Mirror with a surface that curves outward.

40. Convex Mirrors • The rays appear to come from a focal point behind the mirror. • The rays appear to come together but they never actually meet. • The image formed will be virtual and smaller than the object.

41. What is refraction????????????? When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction

42. Section 3 – Refraction and Lenses • When you are looking at fish in a tank, what are the three mediums the light is passing through? Water, glass, air

44. Refraction in Different Mediums • Light bends more in some mediums than in others. • When light passes • from airwater, it slows. • From water  glass, it slows down more. • Glass air it ____________

45. Index of Refraction • The glass causes the light to bend the most, so it has a high index of refraction. • Index of refraction = measure of how much a ray of light bends when it enters the material • The higher the index, the more it bends light

46. Prisms and Rainbows • When white light enters a prism, each wavelength of light is refracted by a different amount • Red has longest wavelength and is reflected least • Violet has shortest wavelength and is reflected most • Same thing happens with water droplets in the air.

48. Mirages • An image of a distant object caused by refraction of light • See page 121.

50. DO NOW • Where are places you see lenses everyday? • What do you know about lenses?