 Top: The formation of a virtual image using a concave lens. Bottom: The formation of a virtual image using a convex mirror. In both diagrams, f is the focal point, O is the object and I is the image, shown in grey. Solid blue lines indicate light rays. It can be seen that the light rays appear to emanate from the virtual image but do not actually exist at the position of the virtual image. Thus an image cannot be seen by placing a screen at the position of the virtual image. To understand images, one must first understand light rays. A light ray is a representation of a beam of light with a vanishingly small diameter (akin to a small diameter laser beam). A small point on any visible object is a source of rays. An infinite number of rays radiate from that point. Image File history File links Download high resolution version (512x773, 21 KB) Virtual image from lens and mirror File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Image File history File links Download high resolution version (512x773, 21 KB) Virtual image from lens and mirror File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
A lens. ...
Reflections in a spherical convex mirror. ...
In optics, the term “object” refers to a source of light (self-luminous or a light reflector). Images are perceived sources of light rays. That is, the light rays do not originate at the image as they do for an object. To form an image one of two circumstances must occur: 1) All the light rays entering the optical device from a single point on the light source are redirected so that they pass through a single point (image location); if one observes the light rays from the proper direction and location, all the light rays will seem to emanate from the image location. 2) All the light rays entering the optical device from a single point on the light source are redirected so that they diverge from each other; if one observes the diverging rays from the proper direction and location they would appear to emanate from a point on the opposite side of the optical device. Case 1 is a real image. Case 2 is a virtual image.
In the illustration, instead of using an infinite number of rays leaving the top of the object for simplicity only two have been drawn in each case. Consider the top illustration. If you were on the opposite side of the lens from the object (looking through the lens at the object), the light rays from the top of the object arrow seem to originate from the top of the image arrow. In the lower illustration, if your eye was behind the object and looking at the mirror, light rays from the top of the object arrow would appear to originate from the top of the image arrow.
If you want to observe both a virtual and real image, all you need to do is get a magnifying glass. In this case, the object (light source) would be what you are looking at through the glass. If the magnifying glass is held near the object, you will see an enlarged image of the object. This is a virtual image. By depth perception, the image will appear to be on the other side of the magnifying glass. If you now move the magnifying glass farther and farther from the object, the image will get larger, then more distorted, and then disappears (this occurs when the object is at the focal length of the lens). If you keep moving the lens farther away from the object and now stand approximately one meter from the magnifying glass, you will now see an upside image. This is now a real image. By carefully seeing how close you can get your eye to the magnifying glass and still see the image should convince you that the image is between you and the lens.
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