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B Image of a virtual object by a plane mirror

  1. Jun 1, 2016 #1
    A plane mirror forms a virtual image of a real object placed in front of it and a real image of a virtual object placed in front of it. I can't picture the second case. Please show me a ray diagram showing real image formation by a plane mirror or just explain the case of real image formation by a plane mirror.
  2. jcsd
  3. Jun 1, 2016 #2
    A real object produces diverging rays, a virtual object produces converging rays.
    A real object placed in front of a converging lens (further than the focal point) will produce converging rays on the other side of the lens. If these converging rays are intercepted by a plane mirror they will appear to come from VIRTUAL OBJECT after reflection by the plane mirror a real image will be formed.
  4. Jun 1, 2016 #3
    I think this is what you are asking. In the following crude drawing, the mirror is vertical, there are two rays that would converge to the right of the mirror to form an image of the tip of the arrow, hence a virtual object for the mirror. By the way, you said "virtual object placed in front of it"; the virtual object is behind the mirror, otherwise rays would diverge from your "virtual object" and you would have the first case you mentioned, a real object.

    The actual rays reflect at the mirror and converge to a real image of the arrow tip to the left of the mirror.

    Last edited: Jun 1, 2016
  5. Jun 1, 2016 #4
    Of course, after making up the drawing I finally found a link: http://www.askiitians.com/iit-jee-ray-optics/reflection-at-spherical-mirrors/

    If you go down the page to the section Virtual and Real Images, the second diagram there shows four rays that would converge to a point if the mirror weren't there, hence a virtual object for the mirror. They converge in front of the mirror to form a real image.

    lychette: not sure what you mean by the rays appearing to come from the virtual object.
  6. Jun 2, 2016 #5
    it is just a choice of words !! Your diagram is exactly what I had in mind. For me the important thing is to realise that converging rays can become a real image or, if they are intercepted, a virtual object. And diverging rays can be from a real object or form a virtual image.
    diagrams are the best way to illustrate the answer.
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