- #1
cuddlesome
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is it possible to have an virtual OBJECT in image formation?
Geometric Optics: Can Virtual Objects Form Images?
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In summary, the conversation discusses the concept of having a virtual object in image formation. It is suggested that using two lenses, with one acting as a virtual object for the other, is a valid method in geometric optics. However, there is some debate about whether this process is a real phenomenon or just a method for analysis. The conversation also touches on the difficulty of understanding optics and the effectiveness of using whiteboard diagrams in teaching the topic.
- #2
Danger
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I don't quite understand the question. Unless there's technical terminology that I'm unaware of, an image is a virtual object.
- #3
cesiumfrog
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I think yes, with two lenses (esp. one diverging), I think you might use one lens to create an image, then put the second lens *before* the image, so that the image for the first lens does not actually form, but acts as a virtual object to the second lens.
- #4
Crosson
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I also thing this is what the OP is referring to, but instead of describing this as a real process I would say it is a valid method of geometric optics (it is not the only method).
- #5
cesiumfrog
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Danger said:
Alas, there is technical terminology in basic (ie. ray) optics (in this case relating to the sign of variables in the lens maker equation) particularly the terms image vs object, real vs virtual, erect vs inverted. An image is only real if you see it when you put a screen there, if you can't do that (typical example is how light seems to emanate from an apparent image *behind* a mirror, where there is no light)
Crosson said:
What do you mean Crosson? In particular, what do you mean by "real process", and what other method are you thinking of?
- #6
Crosson
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cesiumfrog said:
I think of geometric optics as a method for solving for the image of various lens configurations. A final image of an object through configuration of two lenses can be analysed in two ways:
1) Follow key rays through lens1 and use geometry for the (difficult) analysis of these rays when they pass through lens2 (they will not, of course be key rays of lens2).
2) Find the image of the object through lens1, and use this image as the object for lens2 to generate the final image.
There is no question that 1 is valid, but 2 seems more questionable but indeed seems to be valid (although I have never seen a proof of this).
Then I made a comment about the realist interpretation of 2, i.e. did it really happen or is 2 just a method. I don't know.
- #7
cesiumfrog
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2 is the correct way.
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- #8
Danger
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Thanks for the explanation, CF. I think that I'll just stay as far away from optics as I can; it's way too complex. (I have a book about it, but it doesn't help much. 
)
)- #9
cesiumfrog
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I think the problem is just that there are lots of poor ray-diagrams around. If you learn to draw them well, then ray optics is fairly trivial (for example, the lens maker equation is just trigonometry), but if you don't have those tricks/concepts explained/corrected, most students really struggle.
This happens to be the one topic where I've experimented with teaching methods: this may be anecdotal, but after getting every student in a tutorial to contribute in turn to part of a series of ray diagrams on the whiteboard, they performed significantly above average on that topic. Unfortunately I don't know how to apply that technique for teaching other topics, where in practice the problems require a deeper plan.
This happens to be the one topic where I've experimented with teaching methods: this may be anecdotal, but after getting every student in a tutorial to contribute in turn to part of a series of ray diagrams on the whiteboard, they performed significantly above average on that topic. Unfortunately I don't know how to apply that technique for teaching other topics, where in practice the problems require a deeper plan.
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- #10
Danger
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I never realized that you're a teacher; for some reason I assumed that you were a kid (albeit a very well-educated kid).
I can't even begin to understand that book. It's from the 60's or maybe 70's. There are an awful lot of drawings, for sure, but essentially it's like one long equation from beginning to end. There are symbols in there that I don't even know the meanings of, like integrals and such. I remind you that I have a grade 9 math education. I can do simple geometry, but don't know any trig.
I can't even begin to understand that book. It's from the 60's or maybe 70's. There are an awful lot of drawings, for sure, but essentially it's like one long equation from beginning to end. There are symbols in there that I don't even know the meanings of, like integrals and such. I remind you that I have a grade 9 math education. I can do simple geometry, but don't know any trig.
- #11
cesiumfrog
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For the record I'm a just bit of both: PhD student, with some first year tutorials etc on the side.Danger said:
- #12
Danger
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Impressive enough for me.
1. Can virtual objects form images in geometric optics?
Yes, virtual objects can form images in geometric optics. A virtual object is an object that cannot be physically touched but can be seen due to the light rays that it emits or reflects. In geometric optics, virtual objects can form images by reflecting light rays off a curved surface, such as a mirror or lens.
2. How do virtual objects form images in geometric optics?
In geometric optics, virtual objects form images through the process of reflection. When light rays from a virtual object hit a curved surface, they bounce off and converge at a point, forming an image. The size, location, and orientation of the image depend on the shape and properties of the curved surface.
3. What is the difference between real and virtual images in geometric optics?
Real images can be projected onto a screen and can be seen by the human eye. They are formed when light rays actually converge at a point after passing through a lens or reflecting off a curved surface. On the other hand, virtual images cannot be projected onto a screen and cannot be seen directly. They are formed when light rays appear to be coming from a point after reflecting off a curved surface.
4. Can virtual objects form images that are larger or smaller than the object itself?
Yes, virtual objects can form images that are either larger or smaller than the object itself. The size of the image depends on the distance between the object and the curved surface, as well as the curvature of the surface. In some cases, the image may be the same size as the object.
5. Can virtual images be formed without a curved surface?
No, virtual images cannot be formed without a curved surface in geometric optics. The process of reflection off a curved surface is essential for forming virtual images. Without a curved surface, the light rays from a virtual object would not converge to form an image.
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