What is Light

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What is Light???
Electromagnetic Radiation.
Made of Photons
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Where do Photons come from?
An electron gets excited or bumped to a higher
energy level by absorbing a photon with just the
right amount of energy. DE hn
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Where do Photons come from?
The electron then drops back to the ground
state, or lowest possible energy level by
emitting a photon of electromagnetic radiation
DE energy change h Plancks constant n
frequency
h 6.6262 10-34 joule seconds
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Speed of light
v fl
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How fast do Photons travel?
Photons travel at the speed of light
Speed of light 2.997925 x 108 m/s (in empty
space)
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How do we see light??
Light is focused by the lens onto the retina.
The eye is only sensitive to a small range of
electromagnetic radiation, the visible
spectrum. From l 380 nm to 800 nm
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Colors
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Color
The color of an object is due to the object
absorbing all other colors except the one it
reflects. The color an object reflects is the
color it appears to be.
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Reflection Light

• Light is just like any other wave

• Reflection Bouncing back when encountering a
  non absorbing surface

• Ray tracing lines describing the direction of
  propagation of the wave. They describe the
  direction of the wave.

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Ray Tracing
qi q r
Specular Relection, an image is formed
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Reflection from and Uneven Surface
Diffuse Reflection light scatters, so no image
is formed.
Still qi q r
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Plane Mirrors

• Image characteristics
• Virtual image
• Left-right reversed
• Upright image
• Unmagnified image

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Spherical mirrors

• RRadius of curvature
• Ffocal point ffocal length
• Ccenter of curvature

http//micro.magnet.fsu.edu/primer/java/mirrors/co
ncave.html
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Equations for Curved Mirrors
1/f 1/di 1/do
f focal length di distance to the image do
distance to the object
hi/ho -di/do M
hi height of the image ho height of the
object M magnification
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Convenient Rays
Parallel to PA, reflects through f
Goes through f, reflects parallel to PA.
Where the two intersect is where the image is
formed.