Physics Question - Mirror and Lenses

[pacemaker]

I understand the stuff about the mirror but I am confused about the lenses.

 

Lenses create images by refracting light and the observer is always on the opposite side of the lens when compared to the object.....then how can a converging/convex lens create real and virtual images?

 

I am using the TPR book and it says that if i is positive, its a real image (other side of lens) and it i is negative, its a virtual image (same side of lens as object) . I thought that the objects are always real and an image on the same side would be real and the image on the opposite side would be virtual.....I am confused with the underlined part....can someone please clarify/explain that.

 

Thanks!

[Alchemist11]

For mirrors, a virtual object is on the opposite side compared to the incoming light.

 

For lenses, a virtual object is on the same side compared to the incoming light.

 

*I think this is true, someone please correct me if I'm wrong.

 

The way I see it, lenses are meant for light to go through them, therefore if the light rays intersect on the opposing side of the incoming light/object it is real because the light is going in a direction that seems completely normal.

 

On the other hand, mirrors are meant to reflect light, therefore the way light is supposed to go is to remain on the same side as the incoming light/object. So for mirrors when the object and image are on the same side it's real, and not virtual as it would be with lenses.

[Jamone]

I am using the TPR book and it says that if i is positive, its a real image (other side of lens) and it i is negative, its a virtual image (same side of lens as object) . I thought that the objects are always real and an image on the same side would be real and the image on the opposite side would be virtual

 

I think the point of confusion here is that whether the image is real or virtual does not depend on whether it's on the same or opposite side as the object, per say. The determining factor is that an image is real if the light rays actually cross where the image is located, and if the image is virtual if the light rays don't actually cross there. It just so happen that the image is real if it is on the same side as the objects for mirrors, but it is real if it is on the opposite side for lenses.

 

To clarify, look at these two diagrams, one for a mirror and one for a lens. Notice that the light rays cross where the image is located, therefore the images are real.

http://upload.wikimedia.org/wikipedia/commons/e/ef/Lens1.svg

http://en.wikipedia.org/wiki/File:Concavemirror_raydiagram_2FE.svg

 

 

In these diagrams, the light rays do not actually cross where the image is located, therefore the images are virtual.

http://en.wikipedia.org/wiki/File:Lens1b.svg

http://en.wikipedia.org/wiki/File:Convexmirror_raydiagram.svg