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Real vs. virtual images

  1. Dec 3, 2012 #1
    I am struggling on one concept that I cant find when doing a thorough search.

    System: You have a projector (known to project real images onto a screen). The projector expands light with a lens, the light propagates to a flat mirror on a wall and reflects onto a screen.

    Conclusion: Although the image may appear distorted, it is real. It originated from a point and expanded before reflecting onto a screen.

    So, if that conclusion is right, then how is it that a flat mirror can be used a system that produces a real image when every definition basically says "no flat mirrors in a real image system"?

    If the conclusion is wrong and in the system here the image is now virtual, then should I conclude that anything reflected off a flat mirror is virtual? Also, does this mean that a laser shining on a screen is real but a laser shining off a flat mirror on a screen is virtual (same concept, but just double checking)?
    Last edited: Dec 3, 2012
  2. jcsd
  3. Dec 3, 2012 #2


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    Science Advisor

    It can't. Either the mirror is curved, or there is a pinhole you left out.
  4. Dec 3, 2012 #3


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    Science Advisor

    When you look through a mirror, you see a virtual image. You aren't looking through a mirror in this setup. You are looking at a screen. Any time you look at an image projected onto a screen, you are looking at a real image.
  5. Dec 3, 2012 #4
    Thanks, I think I understand the concept completely now.
  6. Dec 3, 2012 #5


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    Staff: Mentor

    In your projector, the lens produces the image. The mirror simply redirects the light so the image appears in a different location than it otherwise would. If you remove the mirror, and maybe cut a hole in the projector, you can probably get an image somewhere, maybe on the ceiling or on a different wall.
  7. Dec 3, 2012 #6


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    This was where you went wrong. I have never read this in any textbook. The connection between real / virtual has nothing, fundamentally, to do with mirrors or no mirrors.
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