Light

1
Light Reflection
2
Electromagnetic Waves
3
Fig. 21.22, p.675
4
The Electromagnetic Spectrum
Section 1 Characteristics of Light
Chapter 13
5

• The most famous and conspicuous supernova
  remnant. The Crab Nebula is the centuries-old
  wreckage of a stellar explosion, or supernova,
  first noted by Chinese astronomers on July 4,
  1054, and that reached a peak magnitude of -6
  (about four times brighter than Venus). According
  to the Chinese records, it was visible in
  daylight for 23 days and in the night sky to the
  unaided eye for 653 days. Petroglyphs found in
  Navaho Canyon and White Mesa (both Arizona) and
  in the Chaco Canyon National Park (New Mexico)
  appear to be depictions of the event by Anasazi
  Indian artists. The Crab Nebula lies about
  6,300 light-years away in the constellation
  Taurus, measures roughly 10 light-years across,
  and is expanding at an average speed of 1,800
  km/s. Surprisingly, its expansion rate seems to
  be accelerating, driven by radiation from the
  central pulsar. Its luminosity at visible
  wavelengths exceeds 1,000 times that of the Sun

6
Crab NebulaX-ray image
Fig. 21.23a, p.676
7
Crab NebulaOptical image
Fig. 21.23b, p.676
8
Crab NebulaInfrared image
Fig. 21.23c, p.676
9
Crab NebulaRadio image
Fig. 21.23d, p.676
10
The Nature of Light

• Light has dual natureParticles and Waves
• Particles of light are called photons
• Each photon has a particular energy
• E h ƒ
• h is Plancks constant
• h 6.63 x 10-34 J s
• Encompasses both natures of light
• Interacts like a particle
• Has a given frequency like a wave
• c f ?

11
Geometric Optics Using a Ray Approximation

• Light travels in a straight-line path in a
  homogeneous medium until it encounters a boundary
  between two different media
• The ray approximation is used to represent beams
  of light
• A ray of light is an imaginary line drawn along
  the direction of travel of the light beams

12
Ray Approximation
13
Electromagnetic Waves, continued
Chapter 13

• Illuminance decreases as the square of the
  distance from the source.
• The rate at which light is emitted from a source
  is called the luminous flux and is measured in
  lumens (lm).

14
Reflection of Light

• A ray of light, the incident ray, travels in a
  medium
• When it encounters a boundary with a second
  medium, part of the incident ray is reflected
  back into the first medium
• This means it is directed backward into the first
  medium

15
Specular Reflection

• Specular reflection is reflection from a smooth
  surface
• The reflected rays are parallel to each other
• All reflection in this text is assumed to be
  specular

16
Diffuse Reflection

• Diffuse reflection is reflection from a rough
  surface
• The reflected rays travel in a variety of
  directions
• Diffuse reflection makes the road easy to see at
  night

17
Law of Reflection

• The normal is a line perpendicular to the surface
• It is at the point where the incident ray strikes
  the surface
• ?i ?r

?
?i
?r
18
Image Formation by a Flat Mirror
Chapter 13
19
Refraction of Light

• The incident ray, the reflected ray, the
  refracted ray, and the normal all lie on the same
  plane
• The angle of refraction, ?2, depends on the
  properties of the medium

20
Concave Spherical Mirrors
Section 3 Curved Mirrors
Chapter 13

• A concave spherical mirror is a mirror whose
  reflecting surface is a segment of the inside of
  a sphere.
• Concave mirrors can be used to form real images.
• A real image is an image formed when rays of
  light actually pass through a point on the image.
  Real images can be projected onto a screen.

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Image Formation by a Concave Spherical Mirror
Chapter 13
Section 3 Curved Mirrors
22
Concave Spherical Mirrors, continued

• The Mirror Equation relates object distance (p),
  image distance (q), and focal length (f ) of a
  spherical mirror.

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Concave Spherical Mirrors,
Chapter 13

• The Equation for Magnification relates image
  height or distance to object height or distance,
  respectively.

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Sample Problem B
25
Mirrors Sign Conventions

• p is the distance to the object
• object in front of mirror
• - object behind mirror
• q is the distance to the image
• - image behind mirror (virtual image)
• image in front of mirror (real image)
• f 1/2C 1/2R
• for concave mirrors
• - for convex mirrors
• M image height/object height hi/ho -q/p
• for upright image
• - for inverted image
• If Mlt1, the image is smaller than the object
• If Mgt1, the image is larger than the object

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Ray Diagram

• Three rays can always be drawn for curved
  mirrors. Where they intersect is where the image
  is located.
• Ray 1 A ray drawn from the object through the
  focal point is reflected parallel to the
  principal axis
• Ray 2 A ray drawn from the object through the
  center of curvature is reflected back on itself.
• Ray 3 A ray drawn from the object parallel to
  the principal axis reflects through the focal
  point.

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Lens Imaging
Lens Type Object Beyond Focal Point Object At Focal Point Object Between Focal Point And Lens
Converging (convex) Real Inverted Reduced Image No Image Formed Erect Virtual Magnified Image
Diverging (concave) Virtual Erect Reduced Image Virtual Erect Reduced Image Virtual Erect Reduced Image
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Sign Conventions for Thin Lenses
Quantity Positive When Negative When
Object location (p) Object is in front of the lens Object is in back of the lens
Image location (q) Image is in back of the lens Image is in front of the lens
Image height (h) Image is upright Image is inverted
R1 and R2 Center of curvature is in back of the lens Center of curvature is in front of the lens
Focal length (f) Converging lens Diverging lens
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Ray Diagrams for Thin Lenses

• Ray diagrams are essential for understanding the
  overall image formation
• Three rays are drawn
• The first ray is drawn parallel to the first
  principle axis and then passes through (or
  appears to come from) one of the focal lengths
• The second ray is drawn through the center of the
  lens and continues in a straight line
• The third ray is drawn from the other focal
  point and emerges from the lens parallel to the
  principle axis
• There are an infinite number of rays, these are
  convenient

30
Fig. 22.16, p.697
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Color
Chapter 13

• Additive primary colors produce white light when
  combined.
• Light of different colors can be produced by
  adding light consisting of the primary additive
  colors (red, green, and blue).

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Color

• Subtractive primary colors filter out all light
  when combined.
• Pigments can be produced by combining subtractive
  colors (magenta, yellow, and cyan).

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Polarization of Light Waves

• Each atom produces a wave with its own
  orientation of E
• All directions of the electric field E vector are
  equally possible and lie in a plane perpendicular
  to the direction of propagation
• This is an unpolarized wave

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Polarization of Light Waves
Chapter 13

• Light can be polarized by reflection and
  scattering.
• At a particular angle, reflected light is
  polarized horizontally.
• The sunlight scattered by air molecules is
  polarized for an observer on Earths surface.

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Polarization of Light, cont

• A wave is said to be linearly polarized if the
  resultant electric field vibrates in the same
  direction at all times at a particular point
• Polarization can be obtained from an unpolarized
  beam by
• selective absorption
• reflection
• scattering

36
Aligned and Crossed Polarizing Filters
Chapter 13
Section 4 Color and Polarization
Crossed Filters
Aligned Filters