Question
Tue November 08, 2011 By:

ray diagrams for convex lens

Expert Reply
Wed November 09, 2011
Each diagram yields specific information about the image. The two diagrams below show how to determine image location, size, orientation and type for situations in which the object is located at the 2F point and when the object is located between the 2F point and the focal point.

A ray diagram for the case in which the object is located in front of the focal point is shown in the diagram at the right. Observe that in this case the light rays diverge after refracting through the lens. When refracted rays diverge, a virtual image is formed. The image location can be found by tracing all light rays backwards until they intersect. For every observer, the refracted rays would seem to be diverging from this point; thus, the point of intersection of the extended refracted rays is the image point. Since light does not actually pass through this point, the image is referred to as a virtual image. Observe that when the object in located in front of the focal point of the converging lens, its image is an upright and enlarged image that is located on the object's side of the lens. In fact, one generalization that can be made about all virtual images produced by lenses (both converging and diverging) is that they are always upright and always located on the object's side of the lens.

 

For the case of the object located at the focal point (F), the light rays neither converge nor diverge after refracting through the lens. As shown in the diagram above, the refracted rays are traveling parallel to each other. Subsequently, the light rays will not converge to form a real image; nor can they be extended backwards on the opposite side of the lens to intersect to form a virtual image.

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