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Optics-Lenses - image outside the mirror?

  1. Jun 24, 2012 #1
    Optics-Lenses -- image outside the mirror?

    A question in my book asks what are the images formed in this diagram:
    http://www.flickr.com/photos/80147355@N05/7362964734/sizes/m/in/photostream/ [Broken]

    I thought there was only one, inside the mirror. But it turns out that there is another one, outside the mirror: http://www.flickr.com/photos/80147355@N05/7362964678/sizes/m/in/photostream/ [Broken]

    I don't get it. How can a thing inside a mirror create an image in midair??
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 25, 2012 #2
    Re: Optics-Lenses -- image outside the mirror?

    You must know that plane mirrors can reflect light (most of) and convex lenses converges the beam to a point (due to refraction). In your diagram , the first image A'B' is formed by refraction of light through convex lens , behind the mirror which is a virtual image . Some of the light energy in the system is also REFLECTED by the plane mirror , shown in diagram by three rays of light which ACTUALLY intersects at a point B'' forming a real image A''B''.

    Note that there will be another image i.e. 3rd image (virtual) by first ray and ray AA' but will be so blurred that you'll not be able to see it. Hence its neglected. (Because the resultant energy in the system will be very negligible.)
    Last edited by a moderator: May 6, 2017
  4. Jun 25, 2012 #3


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    Re: Optics-Lenses -- image outside the mirror?

    This article may help in understanding what a virtual image is: http://en.wikipedia.org/wiki/Virtual_image

    The focal point outside the mirror is where the light actual focuses at. Holding a piece of paper or something at that point will let you see the object in view. The image inside or behind the mirror is a virtual image.
  5. Jun 25, 2012 #4


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    Re: Optics-Lenses -- image outside the mirror?

    A real object will have a virtual image behind a mirror (as we all were taught at School). A real image, projected by a lens, that 'would have been formed' behind a mirror (if the mirror hadn't been there) will be formed as a real image in front of the mirror. This is something that can only be done with a lens as you can't, of course, stick an object behind a mirror and expect a result. :smile:
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