I usually have good results with a scheme like this:
The "natural" order of things in image formation is: Light comes FROM the
object TO the mirror or lens and continues FROM the mirror or lens TO the
image. Either item (object or image) is REAL if it is in its proper
position in this sequence. Otherwise it is VIRTUAL.
So if an image is formed where the light GOES after reflection or
refraction, then it is real; otherwise it is virtual. Similarly for the
object.
Another rule that some students seem to find helpful: The observer sees the
image at the point from which the emerging rays appear to DIVERGE. If the
rays are already diverging as they come from the mirror or lens, then the
image is virtual.
_______________________________________
Fred Lemmerhirt
Waubonsee Community College
Sugar Grove, Illinois
<mailto: flemmerhirt@mail.wcc.cc.il.us> http://chat.wcc.cc.il.us/~flemmerh/physics.html
-----Original Message-----
From: Tina Fanetti [mailto:FanettT@QUEST.WITCC.CC.IA.US]
Sent: Tuesday, March 19, 2002 8:40 AM
To: PHYS-L@lists.nau.edu
Subject: Virtual and Real Images
Hello all
No matter how I try to explain it to my students, I can't seem to get=
across the differences between a real and virtual image.
I told them that a real image could be formed on a screen, a virtual =
could not. A real image is where light converges. There is no conve=
rgences of light rays at a virtual image.
They are still confused and I am at a loss.
Ideas? Thanks
Tina Fanetti
Physics Instructor
Western Iowa Technical Community College
4647 Stone Ave
Sioux City IA 51102
712-274-8733 ext 1429