# Why do we see our image behind the plane mirror?

I know that plane mirrors form a virtual image and virtual images are formed behind the mirror. But I am unable to understand why. I know that the object's light gets reflected back to it through mirrors so when you look at the mirror, you are able to see yourself and your position with respect to the mirror. But to me, it just seems a copy of the real world behind the mirror. I am unable to understand why we perceive the image like this. I feel really confused right now. It could be that I have grasped something wrong. I would appreciate any intuition behind the images formed by mirrors.

• An introductory textbook on geometric optics should be accessible with only high school math and no prior knowledge of physics. Once you get the hang of drawing ray diagrams and applying the law of reflection, I suspect that comprehension of why the world appears copied (but flipped on the axis between you and the mirror) will follow.
– g s
Mar 1 at 8:16
• Your eyes don't know about the mirror, so trace the diagrams from the object to the mirror to the eyes, but then trace them back, through the mirror in a straight line, to see where the object would have to be to make the same rays if the mirror wasn't there. Mar 1 at 15:13
• Hey Kashish. I think your question is more intended towards how our brain interprets an image from a two dimensional surface as a three dimensional reality. Essentially the light from a mirror is reflecting due to the "almost two dimensional" silver layer on the glass and that goes to your eyes but the perception of depth into the image is I think how the brain processes that image . Apologies if i misunderstood your question. Any other expert might extend upon this if this is your question. Mar 2 at 10:14

Think about the formation of a real image of a point.
Light diverges from the point object and some of it passes through the eye's optical which converges the light as a point (real image) on the retina of the eye.
You "see" the point object.

Now consider the point object on front of a plane mirror.
Again light diverges from the point object and is reflected from the plane mirror and continues to diverge and some of it passes through the eye's optical which converges the light as a point (real image) on the retina of the eye. You "see" the point object.

As far as the eye is concerned the two situations are the same in terms of the formation of a real image on the retina of the eye and the eye "sees" a point object.
In the second case the diverging light as it reaches the eye appears to come from a point (which is called the virtual image of the object formed by the mirror) as far behind the mirror as the object is in front of the mirror with the line joining the virtual image and the object perpendicular to the mirror.
If one back produces the rays of light just before they intersect at what is called the virtual image.

So you may ask, So why do perceive them at some distance away from the mirror?
That is where the back produced rays cross and it is where the rays appear to come from.
The rays entering the eye from the virtual image behind a mirror are exactly the same as the rays entering the eye from a real object at that same location without the mirror being present.

The image as seen in the mirror (bottom diagram) is the same distance from the lens as the object in the top diagram.

• So why do perceive them at some distance away from the mirror? That is where the back produced rays cross and it is where the rays appear to come from. The rays entering the eye from the virtual image behind a mirror are exactly the same as the rays entering the eye from a real object at that same location without the mirror being present. Mar 2 at 8:33
• @Farcher Sir imagine if a plane mirror is 4m away from a boy and a cameramen is 7m aways from the plane mirror and the cameramen have to capture the image of boy formed in the plane mirror, So, where the cameramen will focus his camera, At the mirror i.e. 7m away from him OR 11m away from him ?
– user363737
Oct 8 at 6:46
• Sir virtual image is formed behind the mirror, but actually there is nothing behind the mirror what we see is all at the mirror. therefore, camera must be focused 7m away from cameramen but my teacher said it is 11m. Why is that sir ?
– user363737
Oct 8 at 6:54
• @Peterswift That is where the diverging rays which have been reflected from the mirror appear to come from. Oct 8 at 7:54
• @Peterswift I have added two diagrams to illustrate my response to your question. Oct 8 at 8:38