THE SELECTIVE ABSORPTION AND

REFLECTION OF LIGHT

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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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The selective absorption and reflection of light. The color of objects

Thanks for your attention!