Answers to Quest on Vimarsh2

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    AdminCSEC
    Keymaster

    Here are the answers that I have received till today, after extending the closing date by a month.

    Physics Question: We have all seen shiny black objects, e.g. well-polished shoes. These objects are shiny presumably because they reflect light in a certain manner. But … black objects, by definition, are supposed to absorb all incident light.

    So how are the two properties consistent?

    syriac wrote:
    > There are two ways in which light can be reflected from an object:
    > 1) Diffuse reflection: parallel rays are reflected in random
    > directions spreading out everywhere. This happens if the surface is
    > irregular.
    >
    > 2) Specular reflection (as in a mirror): parallel rays emerge as
    > parallel rays. This happens if the surface is smooth.
    >
    > Diffuse reflection gives objects their characteristic color/shade.
    > Which colors in the visible range are reflected depend on the
    > electronic structure of the molecules.
    >
    > Specular reflection causes objects to look shiny because the rays are
    > reflected in a regular manner, and so you can observe a perfect
    > reflection of, say, a light source.
    >
    > A black object can appear shiny if no color in the visible range
    > undergoes diffuse reflection but some surface effect (due to the
    > presence of a chemical coating along with at least partial smoothness
    > due to polishing) causes some of the light to be specularly reflected.
    > Essentially, you have different surface layers that contribute to
    > complete diffuse absorption (black shade) and partial or complete
    > specular reflection (shiny effect).

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