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Homework Help: Curved Mirrors (concave)

  1. May 14, 2006 #1
    how can you tell when the image will become real or virtual in a concave mirror, the distance?..i'm not sure

    thanks in advance

    *edit*
    oh i think i know..is it the magnification, if the magnification is more than 1 then that means its virtual since it would be upright and a bigger image

    is that right?
     
    Last edited: May 14, 2006
  2. jcsd
  3. May 14, 2006 #2

    Hootenanny

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    This is correct;
    Using the standar equation for a mirror;

    [tex]\frac{1}{d_{O}} + \frac{1}{d_{i}} = \frac{1}{f}[/tex]

    When [itex]d_{i}[/itex] is positive, the image is real; if it is negative the image is virtual. [itex]d_{i}[/itex] is the horizontal displacement of the image from the centre of the mirror. [itex]d_{O}[/itex] is the horizontal displacement of the object from the centre of the mirror and [itex]f[/itex] is the focal length of the mirror (which is positive for a concave mirror).

    It is possible it have a real image that is larger than the object. What is the definition of a real and virtual image?

    More information is available here;
    http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/mirray.html#c3
     
  4. May 14, 2006 #3
    Actually if the magnification is +ve , the image is virtual.
    -ve->real
    (As per new Cartesian sign convention)
     
  5. May 14, 2006 #4

    Hootenanny

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    I agree, that's why I said above
    I did forget to mention however, that the image would be inverted.

    ~H
     
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