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Homework Help: Why different objects behave differently with light?

  1. Jul 4, 2006 #1
    We can see our image in a mirror but not in a wall. The explanation is that mirror reflects the light falling on it whereas the wall does not. But if the wall does not reflect light, how can we see the wall?
    Another question, an object reflects some part of light, refracts other and absorbs some part.Why this happens and how does it depends on the nature of matter?
    Why different objects behave diifferently with light?How can the behaviour be explained?

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  3. Jul 5, 2006 #2
    The wall reflects some of the light (not as much as the mirror), but also diffuses it...... the light doesn't necessarily reflect with the same angle of incidence (the wall is not as "smooth" as the mirror).

    An object reflects, absorbs and transmits light. This depends on many many factors. Including whether the material conducts electricity, the crystal structure etc.
    A basic way to think about it can be to assume that electrons act like a mass on a spring. The electric field of the light wave oscillates these and depending on the material the electrons are damped more or less - transmitting the field or not........

    That's a basic way to look at it, if you want to know more, google photonics.
  4. Jul 5, 2006 #3

    Andrew Mason

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    Both the wall and the mirror reflect light. But there is an important difference between the way a mirror reflects light and a wall reflects light.

    At microscopic dimensions, the wall is rough whereas the mirror is smooth (the bumps being smaller than the wavelength of the light). So the light from the wall disperses on reflection but the reflected light from the mirror has the same characteristics at the incident light. Ever wonder why you polish shoes by rubbing really hard to get a nice shiny reflection?

  5. Jul 5, 2006 #4
    Ok I understand the basic idea.
    You are talking about the elctrons in the matter. Right?(If yes, I understood it).
    Now one question about light wave:
    Light is an electromagnetic wave whick can travel in vacuunm. What are sources of oscillating fields in vacuum?
    Now I have wondered on the following question for a long time.We know that waves carry energy from one place to another and we are living in a sea of waves,some of them we use and others remain useless.(e.g radio waves are used only when radio is on, at all the other times energy is wasted)Is there any way to extract energy out of waves?

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