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In the picture below I have a object at half the focus length. I know that the image will create a virtual image. However I was wondering if it was possible to create a real image as well like I have draw.

Secondly I want to clarify on the term real image. Real image means that when your eyes follow the rays it will direct you eyes to an object. In the situation below if we were to move the object to twice the focus length we would have a real image(according to professor). I don't quite understand how the image that is reflected inverted is a real image after all it is reflected by the mirror. Is it a real image because the screen itself is a real object where as with a flat mirror there is no physical object behind the mirror? enter image description here

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  • $\begingroup$ A pair of lines can only intersect once and that point may either be in the same side (real image) or on the other side (virtual image). $\endgroup$
    – Sam
    Jan 7, 2020 at 15:01

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No, the setup you've sketched will not produce a virtual image. The top reflected ray is drawn incorrectly. The top incident ray is hitting the mirror a close to a zero degree angle of incidence. The reflected ray will be angled down through real image. Also, if there were a virtual image, you should be able to extend the bottom reflected ray back behind the mirror to pass through it - the way you've drawn it it isn't even close.

A real image is formed when a setup (mirror, lens, etc) produces rays that diverge from some point in a similar way that that they diverge from an object. This makes that point looks like the object. With a virtual image the rays seem to all diverge from a point but if you trace them back to that point you find that they are redirected by the lens, mirror etc, before you get there.

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  • $\begingroup$ Why would the top ray be incorrect? If we were to look at this backwards, for example if the light was hitting the mirror it would then hit the focus point. Hence shouldn't it not be the same if we hit the mirror wouldn't the ray come back parallel to the principle axis? $\endgroup$
    – coderhk
    May 13, 2017 at 1:46
  • $\begingroup$ If the ray is drawn accurately the angle between the incident ray and the mirror should be the same as the angle between the reflected ray and the mirror. Look at them. They are nowhere near the same. $\endgroup$
    – M. Enns
    May 13, 2017 at 1:53
  • $\begingroup$ That is if the mirror is completely flat. If we have a parabolic mirror and held it against the sun, the sun would be sending parallel rays onto the concave mirror and all the light would pass through the focus point after hitting the mirror. If so then we would draw as if that was the case but backwards since its the same both ways. $\endgroup$
    – coderhk
    May 13, 2017 at 2:04
  • $\begingroup$ The bottom two rays in your diagram will not meet. $\endgroup$
    – Sam
    Jan 7, 2020 at 15:05

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