E-M Spectrum and Waves

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E-M Spectrum and Waves

• Prentice Hall Chapter 18

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Chapter Assignments

• Workbook and E-M Spectrum Activity
• Book
• Section 18.1 535/math practice 1-3 and 538/9,10
• Section 18.2 545/4, 5, 7
• Section 18.5 562/3-7
• 565-67/1-10, 32-35, and FCAT practice

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Review from the last chapter

• Two types of waves are
• Regarding requiring a medium for travel
• Mechanical and electromagnetic
• Electromagnetic does not require a medium
• Regarding shape of the wave
• Transverse and longitudinal
• Electromagnetic waves are transverse waves

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Electromagnetic (E-M) Waves (LIGHT!) Do not
require a medium through which to travel Light
travels at 3.0 x 108 m/s in a vacuum or air Its
wavelength and frequency varies according to the
type of E-M wave
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Higher frequency ? Greater energy ? More
penetration
The full range of frequencies of electromagnetic
radiation is called the electromagnetic
spectrum. Again, all of these forms move at 3.0 x
108 m/s in a vacuum (space) or air. One type to
the left of another type has a longer wavelength
and a lower frequency. For instance radio waves
have a longer wavelength than infrared. Blue
light has a higher frequency than red
light. Electromagnetic waves vary in wavelength
and frequency
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Properties of E-M Waves (Light)

• Light can act as a wave or a particle
• Only a very small portion of the E-M Spectrum is
  visible to humans (between infrared rays and
  ultraviolet rays)
• Those types to the right of the visible portion
  are more penetrating and harmful (can be used to
  look inside or pass through objects) i.e., x
  rays and gamma rays

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c f l c ?

• This formula is used to determine information
  about light.
• Lets say that you know the wavelength of yellow
  light is 600 x 10-7 m. What is its frequency?
  Using c f l
• f c/ l
• f 3.0 x 108 m/s / 600 x 10-7 m
• f 3/600 x 108 7 0.005 x 1015
• f 5 x 10-3 x 1015 5 x 10-315 5x1012 Hz

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Another problem

• Find the frequency of an electromagnetic wave in
  a vacuum with a wavelength of 0.02m
• f c/ l
• f 3.0 x 108 m / 0.02 m
• f 1.5 x 1010 Hz
• Assignment
• 535/math practice 1-3 and 538/9,10

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Behavior of Light

• Materials can affect the behavior of light
• Transparent materials allow most light to pass
  through
• Translucent materials scatter light and makes
  figures appear unclear in appearance
• Opaque materials either absorb or reflect all of
  the light that hits them. No light can pass
  through.

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Interactions

• When light strikes a new medium, the light can be
  reflected, absorbed, or transmitted. When light
  is transmitted, it can be refracted, polarized,
  or scattered.

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Reflection

• When you look into a mirror, light reflects from
  the mirror, and you see yourself
• Because of total internal reflection, laser light
  can travel inside small glass (optical) fibers
  and carry information

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Refraction

• Bending of light as it passes from one medium
  into another. It makes the pencil look
  broken.

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Newton and Prisms

• When white light passes through a prism you see a
  rainbow, because of refraction
• Different colors bend at different angles
• A rainbow is formed when water droplets in the
  air disperse light.

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Colors of objects

• Is dependent upon what the object is made of and
  on the color of light that strikes the object.
• See figure 24 (page 552) in your book

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Primary Colors

• Primary colors of light are Red, green, blue
• Primary colors of
• pigment are
• Magenta, cyan,
• and yellow
• (See page 552
• In your book)

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Red, blue, and green light added together produce
white light. R, blue, and green are primary
colors of light Red plus green produce yellow, a
secondary color Since yellow contains both red
and green, when you add yellow to blue, you get
white light! What about cyan and red? Since cyan
contains green and blue, when you add red, you
get white light again!
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Mixing

• Mix colors of light together, you get more light
  - additive process
• Mix complementary colors
• of light ? white light (blue
• yellow or green magenta)
• Complementary colors
• are opposite each other
• in the color wheel.

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• Mix colors of pigment together, you get less
  light (its absorbed) - subtractive process.
• The primary colors
• of pigment are the
• secondary colors
• of light!

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Assignments

• Section 18.2 545/4, 5, 7
• Section 18.5 562/3-7
• 565-67/1-10, 32-35, and FCAT practice

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Other tidbits about light

• Microwaves are used to communicate between cell
  phones
• Light is produced in the filament of an
  incandescent light bulb when electrons flow
  through the filament
• Sodium-vapor lights are used for lighting many
  streets and parking lots
• Fluorescent light tubes usually contain mercury
  vapor (which give off invisible uv light causing
  phosphors to emit visible light)

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Light shining on objects

• See page 552
• What an object is made of and the color of light
  that strikes it determine the apparent color of
  the object.
• In white light all colors of the object are
  evident
• When other colors of light shine on the object,
  the colors appear very different.

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Laser Light

• Laser stands for Light Amplification by
  Stimulated Emission of Radiation.
• Laser light is coherent - all the waves have the
  same wavelength, direction, and coincidental
  peaks. This means IT IS VERY INTENSE CAN BE
  HARMFUL!!!

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Light - wave or particle?

• A wave when light interferes either
  constructively or destructively

Light is turned on by constructive interference
and off by destructive interference resulting
in an interference pattern (shown at left).
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Light acts as a particle when

• Electrons are emitted from a metal caused by
  light striking the metal during the PHOTOELECTRIC
  EFFECT

Examples Light sensors in cameras, video
cameras, automatic doors. Newton said it acted as
particles because it travels in a straight line
and casts shadows.
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Polarization
Only the blue waves can pass through the opening
in the first card but not through the 2nd card.
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Infra- and Ultra-

• Infra- means under, so infrared light is under
  red light (or to the left in the E-M spectrum)
• Ultra- means above, so ultraviolet light is above
  violet light (or to the right in the E-M spectrum)

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Sources

• Frames 3 4
• concise.britannica.com/ebc/art-70892/The-spec...
• Frame 11
• www.allrefer.com/pictures/s1/r0118400-refraction
• Frame 11
• hyperphysics.phy-astr.gsu.edu/.../refr2.html
• Frame 12
• http//www.physics.ohio-state.edu/gilmore/images/
  collection/misc/prism.gif
• www.britannica.com/eb/art-90651/A-prism-sprea...
• Frame 13
• www.fas.harvard.edu/.../ColorMixing06.jpgFrame
  17
• hyperphysics.phy-astr.gsu.edu/.../lassol.html
• Frame 18
• http//abyss.uoregon.edu/js/images/interference.g
  if