## 20150209

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

Physics 205B, spring semester 2015
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.
"Converging and diverging lenses bend light (and hence images) in different ways. This phenomenon depends on the shape of the lens."

"In the thin lens equation, if f is positive then it's a converging lens but if it's negative then it's a diverging lens, and p and q can be either real or virtual depending on their sign. In a magnification equation, h and h' are the object and image heights, either upright or inverted according to their sign. An image is upright if m is positive and the opposite if it's negative. Finally, if |m| is greater than one then it is enlarged, but if it's less then one then it is diminished."

"A camera consists of a converging lens. In order for it to expose on film, light rays converge to points on the film."

"Elderly people need to hold the object they are viewing at farther distances. This is due to presbyopia diminishing the eyes ability to focus on close objects."

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 presentation of the different variables and equations a little difficult, I hope that we work out some problems on whiteboards to make better sense of it."

"The equations in the book help explain stuff, but still leave it confusing. I don't fully understand m, p, h', h, q, f, and how they all relate to each other."

"As always you going over concepts helps me understand better."

"I found the equations to be confusing. I'm unsure how to apply and use them."

"hich ray tracing fits which picture (in the picto-quiz) and why. Also, maybe some tips on how to draw ray tracing diagrams that are appropriately scaled, sometimes I find that my ray tracings are just slightly off and do not intersect at the exact point."

"There wasn't anything too difficult."

Identify the following thin lens parameters. (Only correct responses shown.)
Focal length: f [83%]
Magnification factor: m [83%]
Object distance: p [79%]
Object height: h [76%]
Image distance: q [79%]
Image height: h' [76%]

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

Lens: converging [78%]
Image: real [69%]
Ray tracing: 1 [67%]

Lens: diverging [50%]
Image: virtual [50%]
Ray tracing: 6 [21%]

Lens: converging [71%]
Image: virtual [48%]
Ray tracing: 4 [24%]

Lens: diverging [36%]
Image: virtual [50%]
Ray tracing: 7, 8, 9 or 10 [31%]

Lens: converging [45%]
Image: real [36%]
Ray tracing: 1 [21%]

Lens: diverging [36%]
Image: virtual [48%]
Ray tracing: 7, 8, 9 or 10 [19%]

Lens: converging [55%]
Image: virtual [57%]
Ray tracing: 5 [36%]

Lens: converging [43%]
Image: real [36%]
Ray tracing: 2 [21%]

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: can see nearby objects [84%]
Hyperopia: can see distant objects [81%]
Presbyopia: can see distant objects [75%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Would presbyopia be a type of hyperopia that just happens when you age?" (Yes, you could think of hyperopia as a congenital (or early childhood development) condition, while presbyopia would be middle age-onset hyperopia.)

"Definitely need to review the ray tracing and picto-quiz." (Will do.)

The homework report portion of this assignment does not have a last name, first name portion but I still submitted it anyway. Just in case all my answers are "I got it okay, with not much difficulty." (Aww, snap. Okay, this just means everybody will get credit for that homework report. EVERYBODY.)