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Real and virtual images from mirrors

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data
    When we look into a mirror, the image formed in virtual as it cannot be captured on a screen. However, If we shine a torchlight at an angle then the beam of light will reflect and form on a screen. But how are we so different from the torchlight's light? Since we simply reflect light into the mirror and the torchlight emits the light so I don't really see the difference.


    2. Relevant equations

    none

    3. The attempt at a solution
    I read that a real image is formed when two or more rays of light converge. While in a virtual image the two rays diverge and the virtual image is formed at the trace. But how do I apply this with the mirrors? Thanks! :-)
     
  2. jcsd
  3. Sep 11, 2012 #2

    CWatters

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    You do get light on the screen but it's NOT an image of the torch.
     
  4. Sep 11, 2012 #3
    Oh. So actually only light is reflected? What is that light actually, just the light being emitted. But aren't they similar as well? Eg I have a projector and I shine a picture on a mirror at an angle. So again the image formed on the screen is "real"? Could you explain the differences to me? Thanks for the help! :)
     
  5. Sep 11, 2012 #4

    CWatters

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    Light striking a point on an object is reflected in all directions. For an image of that object to be formed the light from that point must be focused to a corresponding point in space or on a screen.

    A flat mirror cannot focus the light so cannot make a real image on it's own. Light from a torch can reflect off a mirror onto a screen but what you get is a patch of white light not an image of the filament.

    The image you "see" in a mirror is actually formed by the lens in the eye.

    A projector contains lenses that focus light from the source image to a point. Putting a mirror in the way doesn't really change the projectors ability to do that.
     
  6. Sep 11, 2012 #5
    Oh I understand now. But what about in the torchlight case. Are the rays of light focusing it to a point? Since a image is formed. Or it is similar to having just the sunlight just that the torch's light makes it brighter so a patch is seen?

    And if I'm standing 10 meters of the mirror, then the object is actually the mirror image which is captured by my eyes? So will the distance from the image to my be 20m?
    Thanks for the help! :)
     
    Last edited: Sep 11, 2012
  7. Sep 11, 2012 #6

    CWatters

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    A torch does not project an image of it's own filament. They are designed to project a beam of light of the required angle. eg not focused to a point.

    Yes 20m to the image in the mirror.
     
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