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The selective absorption and reflection of light. The color of objects
CONTENT
1. light absorption
Definition
The law of light absorption
The selective absorption of
light
2. Selective reflection (diffusion) of light. The
colors of objects
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The selective absorption and reflection of light. The color of objects
1.The light absorption
a) Definition
The phenomenon in which a medium decreases the intensity of the light beam going though it is called light absorption.
dd
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The selective absorption and reflection of light. The color of objects
1.The light absorption
The intensity I of a monochromatic light beam after going through an absorptive medium decreases as an exponential function of the distance it travels:
In which: I = intensity of transmitted light (cd)I0 = intensity of incident light (cd) is called absorptive factor
d
I = I0e-αd
b) The law of light absorption
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The selective absorption and reflection of light. The color of objects
1.The light absorption
c) The selective absorption of light
C
J
LL1 L2
F
S
P
Continuous spectrum
Absorption spectrum
Low-pressure sodium lamp
Hydrogen vapor lamp
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The selective absorption and reflection of light. The color of objects
1.The light absorption
c) The selective absorption of light=> Different lights are absorbed differently. In other words, the absorption of light through a medium is selective. => depends on
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The selective absorption and reflection of light. The color of objects
1.The light absorption
• Objects which don’t absorb any light in a part of spectrum are said to be nearly transparent with that part of spectrum• Objects which don’t absorb the visible light are called non-colored
transparent objects • Objects which absorb selectively visible light are called colored
transparent objects • Black objects are objects which can absorb all visible light
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The selective absorption and reflection of light. The color of objects
2. The Selective reflection (diffusion) of light. The colors of objects
For some objects, the ability to reflect (or deffuse) light depends on the wavelength of incident light. Some objects reflect (or deffuse) strongly lights of long wavelength, but reflect (or deffuse) weakly lights of short wavelength.It is called the selective reflection (or deffusion) of light
Wavelength (nm)
Ratio (%)
357 27500 44600 72700 83800 89
1000 90
The ratio of the intensity of reflected light and incident light from the smooth surface of a copper plate
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The selective absorption and reflection of light. The color of objects
Objects appear to have colors since they are able to selectively absorb and reflect certain wavelengths of visible light
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The selective absorption and reflection of light. The color of objects
Summary
• After going through a medium, the intensity of any light……………. As an ………………… function of the ……………………
• Objects ……………..and……………………………lights…………………so that they appear to have……………
• Explain the following experiment.
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