Chapter 14: Light and Reflection

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• Chapter 14 Light and Reflection
• The Sombrero Galaxy
• (www.nasaimages.org)

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Electromagnetic Waves

• Whats comes to mind when you think of the word
  light?
• Generally people only think about sources that
  produce light that is visible to humans

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What is light?

• Light waves are electromagnetic waves
• Remember that electromagnetic waves do not need a
  medium to propagate
• Electromagnetic Wave A transverse wave
  consisting of oscillating electric and magnetic
  fields at right angles to each other.

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EM Waves
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Theres more than what the eye can see

• Not all light is visible to the human eye
• The complete electromagnetic spectrum contains
  many different types of radiation

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The electromagnetic spectrum
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Remembering the Spectrum

• Rabbits Mate In Very Unusual Expensive Gardens
• Red Martians Invaded Venus Using X-Ray Guns
• From Longest Wavelength to Shortest Wavelength
  Radio, Microwave, Infrared, Visible, Ultraviolet,
  X-Ray, Gamma Ray

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Why cant we see the other parts of the EM
spectrum?

• The Suns surface is brightest in the portion of
  the spectrum that is visible to humans

http//apollo.lsc.vsc.edu/classes/met130/notes/cha
pter2/plank_e_sun.html
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Does the Sun emit more than visible light
radiation?
White Light
http//sohowww.nascom.nasa.gov/
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The Milky Way
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Galaxy M101 Across the Spectrum
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All EM waves travel at the speed of light

• Speed of light in a vacuum c 3.00 x 108 m/s
• Speed of light frequency x wavelength

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Brightness

• Brightness at any point is the power per unit
  area at that point (like sound intensity)
• Brightness decreases by the square of the
  distance from the source
• i.e. if you move an object twice as far away from
  a light source, one-fourth as much light falls on
  it

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How bright?

• Lets pretend that a person is looking at a
  candle that is 1 m away from her. If the candle
  were move to a distance of 3 m away, how would
  the brightness change?
• The candle would be 1/9 as bright

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Section 14.2 Flat Mirrors

• Reflection The turning back of an
  electromagnetic wave at the surface of a
  substance

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Enceladus(Moon of Saturn)

• Reflects 99 of EM waves

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Iapetus (Moon of Saturn)

• Light regions Reflect 50-60 of EM Waves
• Dark Regions Reflect 2-5 of EM Waves

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Reflection

• The texture of a surface affects how it reflects
  light
• Diffuse Reflection Rough, textured surfaces
  reflect light in many different directions
• Specular Reflection Smooth, shiny surfaces (i.e.
  water) reflect light in one direction

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Specular vs Diffuse Reflection
Specular Reflection Diffuse Reflection

• When the book says reflection, it means specular
  reflection

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Basic Reflection

• Angle of Incidence (?) Angle of Reflection (?)

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Angles

• Angle of Incidence (?) The angle between the
  incoming light ray and the line perpendicular to
  the surface
• Angle of Reflection (?) The angle between the
  reflected light ray and the line perpendicular to
  the surface

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Flat Mirrors

• Flat Mirrors are the simplest type of mirror
• When an object is placed in front of a flat
  mirror, light rays will spread out from the
  object and reflect from the mirrors surface
• Virtual Image An image formed by light rays that
  only appear to intersect

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Flat (Plane) Mirror Images

• The image produced is upright
• The image is the same size as the object (i.e.,
  the magnification is m 1)
• The image is the same distance from the mirror as
  the object appears to be (i.e., the image
  distance the object distance)
• The image is a virtual image