## 20140209

### Online reading assignment: images produced by lenses, thin lens equations, cameras and eyes

Physics 205B, spring semester 2014
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 examples of images produced by lenses, thin lens equations and camera and eyes.

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.
"I understand the differences and similarities between eyes and cameras, as well as the thin lens equations for eyes and cameras, and I get the basics of linear magnification."

"I understand how a camera and the eye adjusts to objects at different distances in the thin lens equation. The image distance changes with object distance in the camera, but the image distance must be the same for different objects distances with the eye because the size remains constant."

"I understand that cameras and projectors produce real images. Also that farsighted people can see distant objects and nearsighted people can see close objects."

"When one is myopic they have a far point less than infinity, and when one is hyperopic one has too large a near point."

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 am finding it difficult to fully grasp the correlation between ray diagrams and depicting focal, object, image, lengths and converging/diverging lens qualities."

"I confused with the lens equations. I'm not really sure how to use them."

"It wasn't too confusing."

"I had a hard time determining what images would be in the ray diagram by myself I would like to see what other classmates thought the situations were. Also going over the equations and how q and p are related with examples would be beneficial."

Identify the following thin lens parameters. (Only correct responses shown.)
Focal length: f [89%]
Magnification factor: m [91%]
Object distance: p [89%]
Object height: h [77%]
Image distance: q [86%]
Image height: h' [83%]

Identify the type of lens, image, and example ray tracing produced in the online reading assignment examples. (Only correct responses shown.)

Lens: converging [92%]
Image: real [78%]
Ray tracing: 1 [69%]

Lens: diverging [56%]
Image: virtual [61%]
Ray tracing: 6 [43%]

Lens: converging [72%]
Image: virtual [61%]
Ray tracing: 4 [41%]

Lens: diverging [58%]
Image: virtual [64%]
Ray tracing: 7, 8, 9 or 10 [47%]

Lens: converging [67%]
Image: real [58%]
Ray tracing: 1 [34%]

Lens: diverging [64%]
Image: virtual [58%]
Ray tracing: 7, 8, 9 or 10 [36%]

Lens: converging [72%]
Image: virtual [53%]
Ray tracing: 5 [39%]

Lens: converging [69%]
Image: real [56%]
Ray tracing: 2 [39%]

A person with no vision defects can see both nearby and distance objects. Identify what can be seen by a person with the following vision defects. (Only correct responses shown.)
Myopia: nearby objects [97%]
Hyperopia: distant objects [94%]
Presbyopia: distant objects [67%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"If a lens takes light rays coming into it at parallel, then bends them inward toward a focal point, then that lens would be a converging lens. Would it be a diverging lens if it was turned around?" (If it were reversed such that light rays were spreading outwards from the focal point, this lens would then make them parallel. Since this is taking diverging light rays and making them parallel (i.e., "less diverging"), this is still a converging lens.)

"Could we spend some time going through the online picto-quiz examples?"

"That second slide on your camera/lens blog post made me think of: 'Every breath you take, every move you make, I'll be watching you,' by Phil Collins." (Um, did you mean The Police?)