## 20170203

Physics 205B, spring semester 2017
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.
"A converging lens will take parallel rays of light and bring them to a focus at a point in space and a diverging lens will take parallel rays of light and 'defocus' them away from a point in space. The focal point of a lens is the location where parallel light is brought to a focus."

"I saw the tutor and now I understand everything perfectly."

"How to draw out the principal rays, but that was about 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 understand the different types of lenses but am having a tough time drawing them out. Once you go through certain parts of the lens, I am unsure how you determine what kind of ray it is."

"The diverging lens ray tracings on the worksheet were not as intuitive as I thought. Some clarification is definitely needed."

"Real vs. virtual images is confusing. A worked-out example of this would be helpful to explain the intersection of rays of light."

"Still unsure how the focal points work for a diverging lens."

"I am really confused on how to tell if something is classified as a real/virtual image and if it is upright/inverted and/or if it is enlarged/diminished. For example is there something that we should look for so that we can tell if an object is upright and enlarged? If the lines intersect on the left-hand side of the lens does that mean it is a virtual image (for both converging and diverging)? I would like more details on how to properly categorize these things."

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 [72%]
Converging lens 2: real image [76%]
Converging lens 3: (no image produced) [44%]
Converging lens 4: virtual image [56%]
Converging lens 5: virtual image [56%]
Diverging lens 6: virtual image [60%]
Diverging lens 7: virtual image [60%]
Diverging lens 8: virtual image [60%]
Diverging lens 9: virtual image [48%]
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 [36%]
Converging lens 2: inverted, enlarged [32%]
Converging lens 3: (no image produced) [20%]
Converging lens 4: upright, enlarged [12%]
Converging lens 5: upright, enlarged [20%]
Diverging lens 6: upright, diminished [24%]
Diverging lens 7: upright, diminished [20%]
Diverging lens 8: upright, diminished [25%]
Diverging lens 9: upright, diminished [20%]
Diverging lens 10: upright, diminished [24%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This got me as confused as a sea turtle on roller skates."

"I understood how to draw the lines, but not why or what I was doing."

"Can we go over the ray tracing worksheet questions?"

"Please focus more on real/virtual images."

"Let's go over how to identify if something is enlarged/diminished or upright/inverted."