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Name: Yarden
Status: student
Grade: 6-8
Location: N/A
Country: N/A
Date: 6/21/2005


Question:
I have a question regarding where you see the image in a concave mirror when the object is behind the focus point. i have learnt that the image is one that is made with REAL beams of light and therefore you can see the image in a certain place if you have a screen there, but where do you see the image without a screen? (you do, of course, see the image in the mirror after all)


Replies:
Ah, the Real Image and the Virtual Image.

By "behind" the focal point, I presume you mean the situation where both the object and your eyes are fairly distant from the curved mirror, so the magnified view appears inverted. Then there is a "real image" location a little more than 1 focal length from the mirror, on the way to your eyes.

If your head is clamped in a vice, the "image" location nearest your eyes, real or virtual, is the place where the object appears to your eyes to be. That is the "optical science" answer. It's where the rays emerge from. So each eye must focus to that distance, and your pair of eyes must stereoscopically converge on that point.

But usually your head is free, and you will instinctively move your head around to test this image. Then the apparent location and size of such real images shift around slightly, in ways which your experience tells you are inconsistent with the apparent distance to that image. So then they seem a little queer, spacey, mobile, confusing, compared to a direct (no mirrors) view of the object. That is the broader answer, which applies to personal experience and to a wide array of technical fields such as animal sensory systems, robotics, and behavioral science.

This can make it a little difficult to confirm by experience the "ray optics" answer above. Maybe you can discipline yourself to hold your head still and play peek-a-boo with blinders, or peer through two eye-holes in a poster, so if you move, you cannot see. This forces your over-sophisticated brain to accept and use only the focal and stereoscopic information provided by a stationary view.

Jim Swenson



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