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Chapter 18

Chapter 18. Light. Bad: Causes skin cancer Good: produces vitamin D, kills bacteria on surgical tool. Warms you from the sun – skin absorbs wave. Used to treat cancer. AM – amplitude modulation FM- Frequency modulation. White Light – entire range of colors on visible spectrum - ROYGBIV.

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Chapter 18

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  1. Chapter 18 Light

  2. Bad: Causes skin cancer Good: produces vitamin D, kills bacteria on surgical tool Warms you from the sun – skin absorbs wave Used to treat cancer AM – amplitude modulation FM- Frequency modulation White Light – entire range of colors on visible spectrum - ROYGBIV

  3. What is Light? • Light is an electromagnetic wave • Vibration of an electric field and magnetic field together • Electromagnetic waves can travel through space or matter

  4. What is Visible Light? • Light travels at 300,000,000 m/s! • It takes 8.3 minutes to travel from the sun to the earth • It can travel around the earth 7 times in 1 sec

  5. Interactions of Light Waves • Reflection • The bouncing back of a wave when that ray hits a surface that it does not go through

  6. Reflection or Light Source • The moon • Does not produce its own light • Illuminated by the reflection of the sun • Visible object w/o its own light source • Firefly • Luminous • Produces its’ own light

  7. Absorption and Scattering Light • Absorption- when a light beam shines through the air, particles absorb some of the energy – causing the light to be dimmer • Scattering- interaction of light with matter that causes the light to change its energy, direction, or motion

  8. Refraction • Refraction – the bending of a wave as it passes through a material • A prism causes white light to refract and separate into the colors of visible light (ROYGBIV) Red, Orange, Yellow, Green, Blue, Indigo, Violet

  9. Diffraction and Interference • Diffraction – a change in the direction of a wave when it finds an obstacle • Interference – combination of 2 or more waves that result in a single wave • Constructive – greater amplitude • Destructive- smaller amplitude

  10. Light and Color • Transmission – the passing of light through matter • Transparent – allows light to pass • Translucent – transmits but also scatters light • Opaque – does not transmit light

  11. Opaque Objects Color • Objects absorb some light and reflect other • The colors that are reflected determine the color you see

  12. Transparent & Translucent • When the object is colored, you see the color of light that was transmitted through the material

  13. Colors of Light Color Addition – combining colors of light Primary colors of light – red, blue and green Color Subtraction – combining colors of pigment Primary colors of pigment – yellow, cyan and magenta

  14. The Law of Reflection • Light waves are electromagnetic waves. • Light waves travel from their source in all directions • Light is made up of rays that travel in straight lines. • An arrow, called a ray, is used to show the path and direction of light

  15. Mirrors • Law of Reflection – states that the angle of reflection is equal to the angle of incidence. • A ray diagram shows how rays change direction when they strike mirrors and pass through lenses.

  16. Mirrors • 3 types of mirrors • Plane Mirrors • Flat • Concave mirrors • Indent • Convex mirrors • Outdent

  17. Plane Mirror • Plane Mirrors have a flat surface. • Light reflects off a mirror because it can not pass through the surface. • The reflection of an object in a plane mirror is right side up and the same size as the object, but reversed left to right. • Plane mirrors form virtual images. A virtual image is an image through which light does not travel

  18. Ray Diagrams • We use ray diagramsto show how light changes as it strikes mirrors or passes through lenses • Light rays • Going in? Green! • Reflecting out? Red!

  19. Intersections will give you the image location! Plane Mirror Ray Diagrams • First, we draw an image of the object on the other side of the mirror • Distance A is equal to distance B and the image size is the same size as the object size.

  20. Intersections will give you the image location! Plane Mirror Ray Diagrams • Second, we draw light rays from the image to the eye • The image is virtual. Broken lines from the image to mirror indicate virtual rays. Virtual image: Light rays do not actually meet at the image position. Because of that, a virtual image cannot be projected on a screen. • Continuous lines from the mirror to eye indicate the reflected rays.

  21. Intersections will give you the image location! Plane Mirror Ray Diagrams • Third, we join the light rays from the mirror to the object • Lines joining the object to the positions of the reflected rays on the mirror represent the incident rays by following the law of reflection.

  22. Mirror Images • How can I easily describe the image formed? • LOST! L.O.S.T.

  23. L.O.S.T • L- Location: location of the image (in front or behind the mirror). • O- Orientation: which way the image is oriented compared to the original object (upright or inverted). • S- Size: compared to original object is it same size, smaller or bigger? • T- Type: is the image a real image or virtual image?

  24. Plane Mirrors • Characteristics of a plane mirror image: L:Object distance from mirror = image distance from mirror O:Orientation is ALWAYS upright S: Object size = Image Size T: ALWAYS forms a virtual image Image is reversed- left to right

  25. Plane Mirror • Let’s try! • L: • O: • S: • T:

  26. Plane Mirror • L: • O: • S: • T: • Let’s try!

  27. Plane Mirrors • Partner Share • How does the LOST description compare for both of the images produced by plane mirrors?

  28. Concave Mirrors • A concave mirror is curved inward. They can produce both a virtual or a real image. • Real images are in front of the mirror • The point at which light rays meet is called the focal point.

  29. Concave Mirror Can make small objects appear larger Ex: Make-up mirrors, shaving mirrors

  30. How Images Are Formed in Concave Mirrors

  31. Concave Mirrors • When does it make a real image? • Object has to be farther away(behind) from the focal point • When does it make a virtual image? • Object has to be closer to (in front of) the focal point

  32. “OUTSIDE“ the focus Concave Mirrors C F Moving towards the focus, the image is REAL, inverted. It could be smaller, the same size, or larger than the image (depending on the object location)

  33. Intersection will give you the image location! Concave Mirror Ray Diagrams • Pick a point on the top of the object and draw two incident rays traveling towards the mirror. • Using a straight edge, accurately draw one ray so that it passes exactly through the focal point on the way to the mirror. Draw the second ray such that it travels exactly parallel to the principal axis. Place arrowheads upon the rays to indicate their direction of travel.

  34. Intersection will give you the image location! Concave Mirror Ray Diagrams • Once these incident rays strike the mirror, reflect them according to the two rules of reflection for concave mirrors. • The ray that passes through the focal point on the way to the mirror will reflect and travel parallel to the principal axis. Use a straight edge to accurately draw its path. The ray that traveled parallel to the principal axis on the way to the mirror will reflect and travel through the focal point. Place arrowheads upon the rays to indicate their direction of travel. Extend the rays past their point of intersection.

  35. Intersection will give you the image location! Concave Mirror Ray Diagrams • Find the location of the bottom of the object • If the bottom of the object lies upon the principal axis (as it does in this example), then the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object. At this point the entire image can be filled in.

  36. Concave Mirrors • What image was formed? • L: • O: • S: • T:

  37. Concave Mirrors • Let’s try! • L: • O: • S: • T:

  38. Concave Mirrors • Let’s try! • L: • O: • S: • T:

  39. “INSIDE” the focus Concave Mirrors C F Moving towards the mirror, the image is VIRTUAL, UPRIGHT, and gets smaller (although the image is ALWAYS larger than the object itself).

  40. Concave Mirrors • Let’s try! • L: • O: • S: • T:

  41. Concave Mirrors • Let’s try! • L: • O: • S: • T:

  42. Concave Mirror • Characteristics of a Concave mirror image:

  43. Concave Mirrors • Partner Share • How does the LOST description compare for both of the images produced by concave mirrors?

  44. Convex Mirror • A convex mirror is bent outward. The object is virtual and appears smaller and upright. • Convex mirrors spread out light.

  45. Convex Mirrors Can make large objects appear smaller (see a WIDE view) Ex: Security mirrors, driveway mirrors, car door mirrors

  46. Convex Mirror • Characteristics of a convex mirror image: L: Image is ALWAYSbehind mirror O: Orientation is ALWAYS upright S: Object size > Image Size T: ALWAYS forms a virtual image

  47. Note: All rays want to pass through F, but none do Convex Mirrors F C C’ F’ When an object gets closer to the mirror, its image is VIRTUAL, UPRIGHT, and keeps getting smaller (and the images are always smaller than the object).

  48. Intersection will give you the image location! Convex Mirror Ray Diagrams • Pick a point on the top of the object and draw two incident rays traveling towards the mirror. • Using a straight edge, accurately draw one ray so that it travels towards the focal point on the opposite side of the mirror; this ray will strike the mirror before reaching the focal point; stop the ray at the point of incidence with the mirror. Draw the second ray such that it travels exactly parallel to the principal axis. Place arrowheads upon the rays to indicate their direction of travel.

  49. Intersection will give you the image location! Convex Mirror Ray Diagrams • Once these incident rays strike the mirror, reflect them according to the two rules of reflection for convex mirrors. • The ray that travels towards the focal point will reflect and travel parallel to the principal axis. • The ray that traveled parallel to the principal axis on the way to the mirror will reflect and travel in a direction such that its extension on the other side of the mirror passes through the focal point. Align a straight edge with the point of incidence and the focal point, and draw the second reflected ray. Place arrowheads upon the rays.

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