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Chapter 14: Light and Reflection

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Chapter 14: Light and Reflection The Sombrero Galaxy (www.nasaimages.org) Electromagnetic Waves What s comes to mind when you think of the word light? – PowerPoint PPT presentation

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Title: Chapter 14: Light and Reflection


1
  • Chapter 14 Light and Reflection
  • The Sombrero Galaxy
  • (www.nasaimages.org)

2
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

3
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.

4
EM Waves
5
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

6
(No Transcript)
7
The electromagnetic spectrum
8
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

9
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
10
Does the Sun emit more than visible light
radiation?
White Light
http//sohowww.nascom.nasa.gov/
11
The Milky Way
12
Galaxy M101 Across the Spectrum
13
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

14
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

15
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

16
Section 14.2 Flat Mirrors
  • Reflection The turning back of an
    electromagnetic wave at the surface of a
    substance

17
Enceladus(Moon of Saturn)
  • Reflects 99 of EM waves

18
Iapetus (Moon of Saturn)
  • Light regions Reflect 50-60 of EM Waves
  • Dark Regions Reflect 2-5 of EM Waves

19
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

20
Specular vs Diffuse Reflection
Specular Reflection Diffuse Reflection
  • When the book says reflection, it means specular
    reflection

21
Basic Reflection
  • Angle of Incidence (?) Angle of Reflection (?)

22
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

23
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

24
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
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