9 Optical Properties

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    OPTICAL PROPERTIES

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    OPTICAL PROPERTY a materials response to exposure to electromagnetic

    radiation and, in particular, to visible light

    Electromagneticradiation

    energy radiated in theform of a wave consistingof electric and magneticfield components that are

    perpendicular to eachother and also to thedirection of propagation

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    Electromagnetic spectrum spans the wide range from -rays through radiowaves

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    Electromagnetic Spectrum

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    Speed of light in vacuum:

    c = 3 x 108

    m/s

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    LIGHT INTERACTIONS WITH SOLIDS

    When light proceeds from one medium into

    another, the following may happen:

    .

    2. Refraction

    3. Transmission

    4. Absorption

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    REFLECTIONLaw of Reflection

    The incident ray, the reflected ray, and the normal tothe surface all lie in the same plane, and the angle of

    reflection r equals the angle of incidence i.

    r = i

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    2 Types of Reflection1. Specular Reflection when

    parallel light rays strike a smooth,

    plane surface, the reflected raysare parallel to each other.

    Reflections on still water are anexample of specular reflection.

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    Diffuse Reflection when parallel lightrays strike an irregular surface, the

    reflected rays are in various directions

    The image blurs when thewater is rough.

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    REFRACTION bending oflight due to change invelocity

    Index of refraction:

    n = c v

    where c = speed of light in vacuum

    v = speed of light in a mediumvacuum: n = 1

    air: n 1

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    Indices of Refraction for some materials

    Substance n

    Glass 1.523

    Polycarbonate 1.584

    a .

    Diamond 2.419

    Ice 1.309

    Water 1.33

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    Snells Law of Refraction

    When light travels from a material with refractive index n1 into amaterial with refractive index n2, the refracted ray, the incident ray,and the normal to the surface all lie in the same plane. The angle of

    refraction 2 is related to the angle of incidence 1 by

    n1sin1 = n2sin2

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    Transparent materials that are capable oftransmitting light with relatively littleabsorption and reflection

    Translucent materials through which light

    , ,scattered within the interior

    Opaque materials that are impervious tothe transmission of visible light

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    Problems1. A beam of light is traveling in air and strikes a

    material. The angles of incidence and refraction

    are 63 and 21.6, respectively. (a) What is theangle of reflection? (b) What is the index ofrefraction of the material? (c) What is thematerial?

    2. Using a laser and electronic timing device, youfind that light travels 2.5 m within a plastic rodin 11.5 x 10-9 s. What is the index of refractionof the plastic?

    3. What is the speed of light in diamond, glassand water?