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Real/virtual images

  1. Mar 5, 2005 #1


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    When a lens diverges light it is a virtual images, when it converges light it is a real image.

    My teacher said that virtual images cannot be displayed on a screen. We did an experiment and that was the case. But how come we can see with our eyes the virtual image?

    Thanks in advance!
  2. jcsd
  3. Mar 6, 2005 #2

    Andrew Mason

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    The reason you can see an image on a screen is because light rays from a particular point on the real object, which strike the lens surface all over, bend in passing through the lens so that they all converge at a particular point on the other side of the lens (ie at a point on the screen). Light from different places on the object converge at different places on the screen and produce an image of the object (upside down and backward). If the object is too close, the light rays from the object do not converge - they keep spreading out. So they can't form an image on a screen unless you put another lens which takes the diverging light rays and bends them so that they converge. That is what your eye does. It takes those diverging rays and focuses them on the back of your retina to form an image.

    Since your eye is placed a distance behind the lens, the light rays striking the eye have spread apart so the image looks bigger than it really is. (That is why magnifying glasses make things look bigger). I am not sure why it is called a virtual image. It is a real image.

  4. Mar 6, 2005 #3


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    The difference between virtual and real images has to do with where the light rays from a particular point converge. In the case of a magnifying glass, they never actually converge after passing through it, but if you trace their paths back behind the lens (as if they never got bent by it), then they do converge. This convergence never actually happened, though, so it's termed "virtual". The real image we see when we look through the magnifying glass was formed by our eye, not the magnifying glass.
  5. Mar 6, 2005 #4
    The rays entering our eyes when they are diverging are the same as would be obtained if an object were placed at the point where they would meet if extended backwards.

    The mind doesn't distinguish between these two situations and the image is formed on the retina.

    However, since the rays don't actually meet, there is no way to obtain the image on a screen.

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