Cuesta College, San Luis Obispo, CA
Students have a 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 focus parallel rays of light onto a central focal point, where diverging lenses spread parallel rays of light outward, or 'un-focus' them."
"Virtual images are images that are formed in locations where light does not actually reach. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light is coming from this location."
"Converging lenses bring light waves into one focus point. Diverging lenses scatter light waves in outward directions. Diverging lenses produce virtual images, but some converging lenses can produce virtual lenses as well, given specific focal points and object distances."
"In a case-by-case approach, I am confident in my ability to recognize when images are real/virtual, upright/inverted, enlarged/diminished, or non-existent."
"How to connect the ray tracing lines but that is mostly it."
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 found the concept of virtual images a little bit confusing. I also found it confusing how to determine the size and orientation of an image through a lens."
"Most of this."
"I am unsure what the ray going towards the 'secondary F' does to the image with a diverging lens. If a virtual image is produced when the ray going from the source to the center of the diverging lens intersects with the ray going away from the 'primary F,' then the 'secondary F' ray seems to have no purpose."
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 [77%]
Converging lens 2: real image [77%]
Converging lens 3: (no image produced) [44%]
Converging lens 4: virtual image [54%]
Converging lens 5: virtual image [46%]
Diverging lens 6: virtual image [46%]
Diverging lens 7: virtual image [44%]
Diverging lens 8: virtual image [36%]
Diverging lens 9: virtual image [46%]
Diverging lens 10: virtual image [44%]
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 [38%]
Converging lens 2: inverted, enlarged [38%]
Converging lens 3: (no image produced) [47%]
Converging lens 4: upright, enlarged [28%]
Converging lens 5: upright, enlarged [33%]
Diverging lens 6: upright, diminished [31%]
Diverging lens 7: upright, diminished [28%]
Diverging lens 8: upright, diminished [37%]
Diverging lens 9: upright, diminished [36%]
Diverging lens 10: upright, diminished [26%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Could you go over more of the ray tracings, that would help a lot!"
"That ray tracing worksheet made me want to crawl under my desk and cry :'("
"On the ray tracings, do you only need two lines intersecting to produce an image?" (Yes, two lines (if drawn correctly) is sufficient to locate the image, but having all three rays intersecting at the same location is good practice.)
"I'm not sure how an image is either diminished or enlarged."
"What is the difference between a real and a virtual image in the ray tracings? How do I know which is which?"
"Having a hard time visualizing what is the object is and how it is seen through the lens. More specifically I can't visualize clearly yet what my eyes would be looking at. Are my eyes on the left or right side of the drawing? Just confused at this point." (By convention light is traveling from left-to-right, so your eyes would be located on the right side, looking to the left of the page, intercepting these left-to-right traveling rays.)