Cuesta College, San Luis Obispo, CA
Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing presentations on lenses.
Selected/edited responses are given below.
Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Converging lenses bring parallel rays of light and bring them to a focus at a point in space. On the opposite end, diverging lenses take parallel rays of light and spread them out from a point in space. So for the two cases, light either goes to a point or away from a point."
"If the redirected rays of light actually intersect at a location in space, then a real image is generated. If the redirected rays of light do not actually intersect at a location in space, but merely move outwards from an extrapolated location, then a virtual image is generated."
"Lenses and image formation through lenses was the topic of this weeks reading assignment. A focal point occurs when rays near principle axis and parallel to it converge to a singlepoint. Focal length is the distance between the focal point and the lens. Converging lenses cause incident parallel rays to converge to a single point. Diverging lenses cause the rays to move away from each other."
"Regardless of the position of the object that a diverging lens will always produce a virtual image instead of a real one. I understood that the different positions of an object in a convergent lens can produce a real or virtual image that can very in size and postion (inverted or upright)."
"Pretty much the only thing that I understand from the reading and the presentation is how to draw the rays. I can figure out the whole drafting part of it, but everything else is a little confusing. I think I understand the difference between real and virtual images, but I am not very confident in my abilities to do that correctly."
"I really don't understand the lens stuff very well."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"I could use some extra practice on the graphical model of rays, it hasn't quite clicked yet. I haven't grasped the usefulness of drawing rays and making a graphical model out of converging/diverging lenses."
"I can understand ray tracing diagrams fairly well, however I do need to keep practicing to get more comfortable recognizing what is occurring."
"I am still in the process of learning how to distinguish the resulting image as upright/ inverted, enlarged/diminished and real/virtual and how to identify and the definitions."
"All the lenses stuff seems confusing to me. I'm not sure when things are enlarged or not and I'm not sure how to tell if an image will be real or virtual by looking at the line drawings."
A lot of this was confusing. I still don't really get the whole labeling part of the images (upright/inverted, enlarged/diminished). I am also kind of confused about how to find the convergence point or location of the object or whatever that is. Very confusing. Hopefully this will make more sense in class. :)"
"The linear magnification equation."
Complete the online reading assignment ray tracings as best as you can. Identify the type of image produced for each ray tracing. (Only correct responses shown.)
Converging lens 1: real image [63%]
Converging lens 2: real image [71%]
Converging lens 3: (no image produced) [29%]
Converging lens 4: virtual image [60%]
Converging lens 5: virtual image [43%]
Diverging lens 6: virtual image [54%]
Diverging lens 7: virtual image [51%]
Diverging lens 8: virtual image [46%]
Diverging lens 9: virtual image [54%]
Diverging lens 10: virtual image [49%]
Complete the online reading assignment ray tracings as best as you can. Identify the image orientation and size produced for each ray tracing. (Only correct responses shown.)
Converging lens 1: inverted, diminished [47%]
Converging lens 2: inverted, enlarged [37%]
Converging lens 3: (no image produced) [26%]
Converging lens 4: upright, enlarged [26%]
Converging lens 5: upright, enlarged [34%]
Diverging lens 6: upright, diminished [46%]
Diverging lens 7: upright, diminished [40%]
Diverging lens 8: upright, diminished [43%]
Diverging lens 9: upright, diminished [43%]
Diverging lens 10: upright, diminished [37%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Honestly I think all of those are wrong. I was having a hard time figuring out what the rays meant based on their orientation. *Confused*"
"Can we discuss what happens with a converging lens when an object is located on its focal point?"
"I don't think I quite know how to tell if the image is upright/inverted or diminished/enlarged."
"Do you think for this particular section that it might be best to extensively read your presentations and take more from them than the chapter in the book?" (At least for now, perhaps. Later, the textbook will go into more detail especially for corrective optics.)
"I am severely confused."
"I have no idea what's going on this worksheet."
"This is very confusing and I am looking forward to seeing how you make this make sense."
"I'm a bit confused on which ray tracings this reading assignment is referring to. Is that referring to the handout from class?" (Yes.)
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