Download - Electromagnetic Radiation … aka Light
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Electromagnetic Radiation … aka Light
The EM spectrum•Not just the “light” we can see…•Ranges from low frequency radio waves to high frequency x-rays•Small window of frequencies called “visible light”
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Light Properties: Review• Electromagnetic radiation travels Electromagnetic radiation travels
________________in a vacuum ________________in a vacuum
– or about 186,000miles/secondor about 186,000miles/second
• This velocity has a symbol of?This velocity has a symbol of?
• Travels in rays… straight line from an origin.Travels in rays… straight line from an origin.
3.00 3.00 E8E8 m/s m/s
cc
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Visible Light • A small slice of the EM spectrum can be detected A small slice of the EM spectrum can be detected
by human eyes.by human eyes. • ColorColor is the brains code for the frequency of is the brains code for the frequency of
perceived light.perceived light.• Roy G. Biv – acronym Roy G. Biv – acronym • On the left are low frequencies and long On the left are low frequencies and long
wavelengths. On the right are high frequencies wavelengths. On the right are high frequencies and short wavelengthsand short wavelengths
R O Y G B I V
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Color # 1- Rules for Color
• White is ALL colors of the VS (visible spectrum)
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Color # 1- Rules for Color• Black is the absence of all colors.• Black appears black because nothing is
reflected from it… therefore the light energy is turned to heat!
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Color # 1- Rules for ColorColor # 1- Rules for Color• Objects of a particular color absorb all other Objects of a particular color absorb all other
colors except for the color they “normally” colors except for the color they “normally” appear.appear.
• Ex. Green plants absorb all colors (roybiv) Ex. Green plants absorb all colors (roybiv) and use these energy frequencies to and use these energy frequencies to produce sugar during photosynthesis…, produce sugar during photosynthesis…, except green… they reflect green.except green… they reflect green.
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Color # 2- Rules for Color
• An object’s color depends SOLELY on the color of light that is reflected off of it.
White light (roygbiv)
Green o
nly is
reflect
ed
Object looks green
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Color # 3- Rules for Color
• An object’s color depends SOLELY on the color of light that is reflected off of it.
No light is reflected, no light reaches the eye, so object appears black!
The turtle absorbed red light
Filtered red light
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Velocity of light through other Velocity of light through other materials – Snell’s Lawmaterials – Snell’s Law
• When light travels through substances, its velocity is effected.
• The amount the speed is reduced is the optical density (n)
• n = c / velocity in the substance
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Find the v of each of these.Material nVacuum 1.0000Air 1.0003Ice 1.31Water 1.333Ethyl Alcohol 1.36Crown Glass 1.52Zircon 1.923Diamond 2.417
n = c/v
3.00 E8 m/s3.00 E8 m/s2.29 E8 m/s2.25 E8 m/s2.21 E8 m/s1.97 E8 m/s1.56 E8 m/s1.24 E8 m/s
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Law of Reflection• Establish “normal” – an imaginary
perpendicular line to the surface of a reflective object.
mirror
normalnormal
ΘAngle of
incidence
i ΘrAngle of reflection
=
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Inverted imagesInverted images• Mirrors produce images which have an
“apparent distance” equal to that of the real object is from the mirror.
• Images are also “inverted”• Mirrors need not be the same size as the object
to produce a full sized image.
d d
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Mirrors and Reflection• Light rays travel in parallel rays from a
source to an object that reflects them.
• A reflection can be “diffuse”, “perfect”, or “focused”
• Mirrors create either perfect (specular) or focused reflections depending on their shape.
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Diffuse Reflection• The rays are scattered in different directions.
This is the way we see most objects in everyday life.
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Perfect (specular) reflection
• Plane mirrors create perfect parallel reflection of rays.
mirror
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Focused reflection• Concave and Convex Mirrors create
focused reflections. They still obey the Law of Reflection.
• ConvexConcave Focal
point
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Mirrors and Reflection #4enlarged
Multiple normals, resulting in slightly different reflected
angles
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RefractionRefraction• High frequencies are more affected by this
phenomenon.
• Snell’s Law also predicts how much it will be bent in the equation…
ni sinΘi =nrsinΘr
• n = optical density or Index of refraction.
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Refraction#1
When light changes the material in which it travels, changes in velocity cause a change in
direction. The θincidence is different than the θrefracted.
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Refraction#2
Optical density of the material determines amount of “bending”
Optical density low
Optical density high
Optical density low
High O.D. = small ΘLow O.D. = larger Θ
parallel
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water
air
Actual fishVirtual fish
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LensesLenses• Lenses obey Snell’s Law by refracting light to a
certain degree.• Lens shape has the biggest effect on light
behavior.• Two types :
Concave Convex
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Renaissance Masters - Tracers???
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