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I have seen this question: Why can you see virtual images? but answers evade the question. Light needs to hit the retina in order, what is the meaning of "dashed" lines in most visualizations that track the light back near the original object? Can someone clarify? Is it reflected?

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Your eye can't tell what happened to the light ray on it's way towards your eye. All your eye can tell is what angle the light rays hit it. (The eye doesn't actually measure angles of course, it measures the angle indirectly by adjusting it's focal length to get a sharp image.)

If you have a real object then light scattered by that object reaches your eye and the eye adjusts its focus to make the rays converge on the retina. In this case the image is of a real object, and the lines you draw on your ray diagram are actually the lines travelled by the light rays.

With a virtual image the light rays reach your eye at the same angles as if they had come from a real object, but due to some cunning arrangement of lenses the light rays changed direction at some point before they reached your eye. In that case your eye is fooled into seeing the light rays coming from an object that isn't actually there, because it can't tell the light rays changed direction. When you draw the ray diagram the lines from the eye out to the cunning arrangement of lenses are drawn as solid because that's actually the path the light took. However at the lens the light changes direction, so you have to extrapolate the lines from the eye to see where the eye thinks the object was. The lines are drawn dotted because they show where the eye thinks the light is coming from rather than where it actually came from.

John Rennie
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