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Unit 3 Light and Optical Systems

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Unit 3 Light and Optical Systems Topic 1 What is Light? Remember to name and date your notes! – PowerPoint PPT presentation

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Title: Unit 3 Light and Optical Systems


1
Unit 3 Light and Optical Systems
  • Topic 1
  • What is Light?

Remember to name and date your notes!
2
  • Light is the form of energy you can see. This
    energy can be produced naturally by the sun or
    fire, or artificially by light-producing
    technologies, like batteries.

3
  • Radiation is the wave like transfer of light from
    its source in all directions.
  • Light is often called radiant energy. Light from
    the sun is formed by nuclear fusion.

4
  • Less than one millionth of one percent
    (0.00000001 ) of the suns energy actually
    reaches earth!

5
  • Because sunlight is not always available, we have
    developed artificial light sources.

6
  • Artificial Light Sources
  • Incandescent heat causing a metal filament to
    glow
  • Fluorescent ultraviolet lights (high-energy) is
    absorbed by particles and then emitted
  • Phosphorescent same as fluorescent, but light
    is emitted over time rather than immediately.

7
  • NATURAL LIGHT SOURCES
  • Sun, Fire (wood), Candles and Oil Lamps
  • Bioluminescence light produced by living
    organisms.

8
  • Chemiluminescent light released by chemical
    reactions (can be natural or artificial.)

9
  • When light reaches a surface, it can be absorbed
    and transformed into other types of energy

10
  • into electrical energy (solar cells change
    light into electricity) into thermal energy (a
    hot road in summer) into chemical energy (trees
    absorb sunlight and make sugars)

11
  • The amount of energy a surface receives depends
    on the intensity of the light.
  • The more intense the light, the more light can be
    absorbed.
  • (think of a hot road on a sunny day, versus the
    temp. of the road on a cloudy day)

12
  • Light travels in straight lines until it strikes
    a surface.
  • The type of surface will determine how the light
    will continue.

13
  • If the surface is transparent, the light
    continues in a straight path through the object
  • If the surface is translucent, the light will be
    diverted (refracted) after it passes through
  • If the surface is opaque, the light will be
    blocked and not allowed through the object

14
Unit 3 Light and Optical Systems
  • Topic 2
  • Reflection

Remember to name and date your notes!
15
  • Reflection is the process in which light strikes
    a surface and bounces back off that surface.
  • How it bounces off the surface depends on the Law
    of Reflection and the type of surface it hits.

16
  • If light hits a rough surface, the light is
    scattered...

17
  • If it hits a smooth surface, the light reflects
    at an opposite angle to the angle it hits.

18
  • Light coming from a light source is called an
    incident ray and the light that bounces off the
    surface is called a reflected ray.

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  • A line that is perpendicular (90 degrees with the
    surface) to the plane mirror is called the normal
    line.

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  • The angle between the incident ray and the normal
    line is called the angle of incidence ( i ). The
    angle between the reflected ray and the normal
    line is called the angle of reflection ( r ).

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  • Mirrors that bulge out are called Convex mirrors.
  • Mirrors that cave in are called
  • Concave mirrors.

25
  • Convex mirrors form images that appear much
    smaller and farther away than the the object -
    but they can reflect light from a large area,
    making them useful as security devices.

26
  • Concave mirrors form an image that appears to be
    closer than it actually is and can be useful
    because it can also reflect light from a large
    area - side mirrors on automobiles.

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Unit 3 Light and Optical Systems
  • Topic 3
  • Refraction

Remember to name and date your notes!
31
  • Refraction is the process in which light is bent,
    when it travels from one medium to another.
  • Light bends because it changes speed when it
    moves through materials that have different
    densities.

32
  • Light travels slower in materials that are more
    dense, because there are more particles. The
    bending of light makes the object's image appear
    to be in a different position than it really is.

33
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  • The Law of Refraction
  • when light travels from one medium, to a more
    dense medium, the light will be bent toward the
    normal,
  • See Image A

35
Image 'A'
36
  • and when it exits the denser medium into a less
    dense medium, it will bend away from the normal.
    The new direction of light is called the angle of
    refraction.
  • See Image B

37
Image 'B'
38
  • Refraction can also occur when light travels
    through air at different temperatures, because
    warm air is less dense than cold air. The
    refraction of light through air is called a
    mirage.

39
  • When air near the ground warms, the light from
    objects at a distance is refracted into a curved
    path. This causes the illusion of a water
    surface, which is really an image of the sky
    refracted by warm air near the ground.

40
Mirage
41
Behaviour What happens to light? Nature of surface What else happens?
Absorption Changes into some other kind of energy Mostly rough, dark, opaque surfaces Some light is reflected
Reflection Bounces off surface, travels in new direction. Best when light hits smooth shiny surface Some light is eventually absorbed
Refraction Travels through the surface, into a new direction When light hit a different transparent medium Some light is usually reflected off surface.
42
Unit 3 Light and Optical Systems
  • Topic 4
  • Lenses and Vision

Remember to name and date your notes!
43
  • A lens is a curved piece of transparent material
    (glass/plastic).
  • When light rays pass through it, the light is
    refracted, causing the rays to bend.

44
  • A double concave lens is thinner and flatter in
    the middle than the edges.

45
  • Light passing through the thicker more curved
    areas of the lens will bend more than light
    passing through the thinner areas, causing the
    light to spread out or diverge.

46
  • A double concave lens

47
  • A double convex lens is thicker in the middle
    than around the edges.
  • This causes the light to come together at a focal
    point, or converge.

48
  • A convex lens refracts the light rays from an
    object so they can be focused.

49
  • Different size lenses can converge the light rays
    at different distances, enabling corrections to
    be made to focal points.

Here is the focal point.where light comes
together after passing through the lens.
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51
  • The lens in the human eye is a convex lens, which
    focuses the light rays entering your eye to a
    point on your retina (a light sensitive area at
    the back of the eye).

52
  • The image you see is formed on the retina.

53
  • Some people however have eyes that are too long
    or too short.
  • If their eye is too long, the image forms in
    front of the retina - this is a condition called
    near-sightedness

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55
  • If their eye is too short, the image forms behind
    the retina, making object that are close to them
    difficult to see. This condition is called
    far-sightedness.

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  • Notice anything odd about this?

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59
Unit 3 Light and Optical Systems
  • Topic 5
  • Extending Human Vision

Remember to name and date your notes!
60
  • In a refracting telescope, light from a distant
    object is collected and focused by a convex lens.
    A second lens, called the eyepiece lens, works as
    a magnifying glass to enlarge the image.

61
(CONVEX)
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  • A reflecting telescope uses a concave mirror to
    collect rays of light from a distant object. This
    mirror forms an image which is then magnified by
    the eyepiece lens.

64
(CONCAVE)
65
  • Binoculars - two reflecting telescopes mounted
    side by side. In binoculars, the telescopes are
    shortened by placing prisms inside, which serve
    as plane mirrors. In this way, the light entering
    the binoculars can be reflected back and forth
    inside a short tube.

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67
Unit 3 Light and Optical Systems
  • Topic 6
  • The Source of Colors

Remember to name and date your notes!
68
  • When white light is refracted into different
    colors, the resulting pattern is called a
    spectrum.

69
  • ROY G BIV

70
  • When light strikes an object, it can be absorbed,
    reflected, or refracted (transmitted).
  • Why is an apple red?
  • Why is celery green?
  • Why is your shirt blue?

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72
  • Why does a piece of paper appear white?
  • Why does the ink in a textbook appear black?
  • The white paper reflects all colors, while the
    black ink absorbs all colors.

73
  • Additive Primary Colors
  • Red Green Blue
  • -all three working in the right amounts will
    create white.

74
  • Secondary Colors
  • -created when two primary colors are put together
  • Yellow Cyan Magenta

75
Rods detect the presence of light. Cones
detect color. There are three types, each
responding to a different color. Red, Green,
Blue. Signals from these cells travel through
the optic nerve and to the brain where the brain
determines shape and color.
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77
  • The cone cells in some peoples eyes are unable
    to detect certain colors. (Ask Mr. Helgren!)
    This is colorblindness.
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