Physics quiz archive: lenses, optical instruments

Physics 205B Quiz 2, spring semester 2019
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz02B3rD



Sections 30882, 30883 results

0- 6 :
7-12 :	*** [low = 7]
13-18 :	*****
19-24 :	********************* [mean = 21.5 +/- 5.2]
25-30 :	****** [high = 30]

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

Physics 205B, spring semester 2020
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 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 lenses cause light rays to converge toward a focal point, while diverging lenses cause light to diverge (spread out). Converging lenses can produce either real or virtual images, while diverging lenses can only produce virtual images. The thin lens and magnification equations help us determine the location, size, and nature of the image a lens produces."

"I understand the image tracings a little bit better. I understand how the height and what side of object the image is on effects the the orientation and size of the image. I also understand that if the lines can be traced back that makes the image virtual."

"When drawing ray tracings, rays move from left-to-right with the object located on the left of the lens. Once the tracing is complete, if it is a virtual image, then the image would be located on the left of the lens. If the image is real then the image will be located to the right of the lens."

"The magnification equation uses the ratio of image height to object height, or the negative value of image distance to object distance. Regardless of whether or not the image is enlarged or diminished, an upright image will always have a positive height value and an inverted image will have a negative height value."

"How the thin lens equation and magnification equation are derived. I understand the basics of the thin-lens and magnification formula. I understand how near point is corrected for someone who is farsighted and how the far point is corrected using a diverging lens for someone who is nearsighted."

"This section is still on converging and diverging lens, however, it talks about how cameras and eyes are similar because they are both converging lens which produce real images. Camera have a fixed focal length lens meaning on the image and object distance is the only thing influencing its equation. Eyes have fixed image length distance since the eye is constant. This means that only object distance and focal lens are then only factors that can change."

"The difference in the different 'sighted-nesses.' Myopia being nearsighted, meaning they can see things near to them better. Versus hyperopia being far-sighted meaning they can see things far to them better. I have heard of these terms before, but it is cool to know the physics behind 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.

"Real and virtual images are still giving me a little but of trouble. I am always unsure on my answers. Also comparing ray tracings was oddly difficult."

"I'm still struggling to understand how to distinguish between real/virtual, upright/inverted, and enlarged/diminished images."

"I'm still confused about what kind of image is produced through each lens, whether the image is real, virtual. I'm also not sure how to apply the thin lens equation."

"I'm still having trouble with the distinction of real image versus virtual image. Diverging lens are always virtual I believe but need more refreshing of these concepts."

"I do not understand the sign conventions for lenses, drawing ray tracings might help. The sign conventions were just given as a list in the book so it's hard to relate them to images being formed."

"How to use the thin lens and magnification equations correctly in-relation to examples. Need some example problems and discussion to process this quantitatively to the best of my ability."

Identify the following thin lens parameters. (Only correct responses shown.)

Focal length: f [91%]
(Linear) magnification factor: m [89%]
Object distance: d_o [94%]
Object height: h_o [83%]
Image distance: d_i [86%]
Image height: h_i [94%]

For a simple camera, identify which parameter(s) must change or remain constant in order to focus on different distance objects.

Focal length: remains constant [49%]
Lens-to-film distance: changes [60%]

For a model eye, identify which parameter(s) must change or remain constant in order to focus on different distance objects.

Focal length: changes [80%]
Lens-to-retina distance: remains constant [74%]

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

Lens: converging [66%] (Only converging lenses can make inverted images.)
Image: real [63%] (All inverted images are real.)
Ray tracing: 1 [46%]

Lens: diverging [43%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [46%] (All upright images are virtual.)
Ray tracing: 6 [26%]

Lens: converging [60%] (Only converging lenses can make upright, enlarged images.)
Image: virtual [46%] (All upright images are virtual.)
Ray tracing: 4 [20%]

Lens: diverging [49%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [49%] (All upright images are virtual.)
Ray tracing: 7, 8, 9 or 10 [31%]

Lens: converging [40%] (Only converging lenses can make inverted images.)
Image: real [40%] (All inverted images are real, as the candle is upright, and the projected image is upside-down.)
Ray tracing: 1 [11%]

Lens: diverging [51%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [54%] (All upright images are virtual.)
Ray tracing: 7, 8, 9 or 10 [28%]

Lens: converging [60%] (Only converging lenses can make upright, enlarged images.)
Image: virtual [46%] (All upright images are virtual.)
Ray tracing: 5 [29%]

Lens: converging [54%] (Only converging lenses can make inverted images.)
Image: real [46%] (All inverted images are real, as the slide is upside-down, making the projected image on the wall upright.)
Ray tracing: 2 [26%]

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 [97%]
Hyperopia: can see distant objects [97%]
Presbyopia: can see distant objects [91%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Can we please go over real and virtual images again in the examples above? I wasn't sure how to identify the ray tracings."

"I really just don't understand how we can tell whether an image is produced from a converging or diverging lens. So confused!"

"I feel that I need a lot of help with the lenses and real-life examples because I feel lost."

"Is the difference between concave and convex lenses the same as the difference between converging and diverging lenses?" (Yes, exactly.)

"I'm really unsure of how to distinguish between what produces a real or virtual image just based on the object. I feel like I missed a blog presentation that explained this because I've looked through them and I can't seem to find the best resource to help me understand them. I can see on the worksheet where the light rays intersect (or don't) if they are real or virtual and also if they are upright or diminished. I just don't know how we can determine this just be knowing what object light isis passing through. Maybe I am missing something really obvious?" (We officially didn't have a super-specific reading or lecture on this, but we had a flowchart to determine whether an image or real or virtual, and this process is something we'll pick up from practice rather than from strict formal definitions.)

"I thought this chapter was very intriguing because of its relation to human anatomy."

"Is it accurate to say that you can see a real image without having to look directly through a converging lens but in order to see a virtual image you have to look through the lens that produced it?" (Yes. You can only project a real image onto a screen, as you'll be doing in lab this week. You can see both real or virtual images by looking back through the lens.)

"Interesting material, also it's just been so cold in the mornings lately!"

Online reading assignment: lenses

Physics 205B, spring semester 2020
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 focal point is the point at which rays or waves meet after reflection or refraction and the distance between the focal point and the lens is the focal length."

"Converging lenses refract light to a focal point and that diverging lenses refract light away from a point in space. In certain cases the image produced can be diminished, enlarged, upright or inverted."

"The distance that an object is from a lens determines where it is shown. It may also be inverted based on the distance from the lens."

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 do not understand real vs virtual images. I think I have a small grasp on both terms but why one is considered real and the other not, confuses me. Also every one of my diverging lens rays is the same which cannot be right."

"I'm not sure when the image projected is diminished, enlarged, upright or inverted. I also am not sure how to draw ray tracings for when the object is in front of the secondary focal point."

"The parts that seem confusing are the principal rays for converging lens. As well as the principal rays for diverging lens. I definitely found the ray tracing worksheets confusing."

"I had trouble figuring out when an image would be enlarged or diminished."

"Could work on drawing better."

"Nothing confusing I just want more practice to solidify my understanding."

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 [65%]
Converging lens 2: real image [70%]
Converging lens 3: (no image produced) [46%]
Converging lens 4: virtual image [41%]
Converging lens 5: virtual image [46%]
Diverging lens 6: virtual image [38%]
Diverging lens 7: virtual image [38%]
Diverging lens 8: virtual image [35%]
Diverging lens 9: virtual image [38%]
Diverging lens 10: virtual image [38%]

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 [62%]
Converging lens 2: inverted, enlarged [54%]
Converging lens 3: (no image produced) [44%]
Converging lens 4: upright, enlarged [49%]
Converging lens 5: upright, enlarged [51%]
Diverging lens 6: upright, diminished [41%]
Diverging lens 7: upright, diminished [38%]
Diverging lens 8: upright, diminished [30%]
Diverging lens 9: upright, diminished [35%]
Diverging lens 10: upright, diminished [32%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I need a lot of help understand real and virtual images. I do not understand how to tell the difference."

"May we review real/virtual images? I found that quite confusing."

"Can we please see each ray tracing in class so I know if I drew mine right?"

"I have questions about drawing the rays."

"More individual ray worksheets would be awesome!"

"I drew the rays but I'm still not sure what I'm looking at..."

"This is going to take some getting used to."

"Why can't diverging lenses create an image larger than the object?" (When a diverging lens makes an image from an object, the resulting image will always be smaller. However, if a diverging lens takes light that passed through another lens first (making it a virtual object, which we won't get into this semester, as those ray tracings are pretty intense), then the resulting image can be bigger than the original object!)

"Also out of curiosity how old is P-dog?" (I'm old. Old AF.)

Physics midterm question: comparing diverging lens image sizes

Physics 205B Midterm 1, spring semester 2019
Cuesta College, San Luis Obispo, CA

An object 1.0 cm in height is placed 16.0 cm in front of a f = –15.0 cm diverging lens, producing an image. Show that moving the object slightly closer, such that it is 14.0 cm in front of this diverging lens will result in a slightly larger image than before. Explain your reasoning by using ray tracings and/or thin lens equations, properties of lenses, images, and magnification.

Solution and grading rubric:

• p:
  Correct. Proves that the object should be as close to the diverging lens as possible in order to obtain the largest image (largest linear magnification factor) using either of these two methods:
  1. calculating the image distances produced by the different object distances, and finds the resulting respective image sizes and/or linear magnification factors; or
  2. drawing two carefully, properly scaled ray tracing diagrams.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have misplaced values, but consistently interprets resulting numbers.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. Problematic algebra (combines fractions by combining denominators, forgets to invert (1/f – 1/d_o) to solve for d_i, etc.).
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of lenses, images, and linear magnification. Typically has problematic algebra as in (t), but does not use (erroneous) d_i values to find image heights or linear magnification factors for comparison.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of lenses, images, and angular magnification.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01Ft6G
p: 25 students
r: 6 students
t: 4 students
v: 4 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 1810), using two sets of thin lens equations:
Another sample "p" response (from student 0691), using two ray tracings:

Physics quiz archive: lenses, optical instruments

Physics 205B Quiz 2, spring semester 2019
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz02BTLn



Sections 30882, 30883 results

0- 6 :
7-12 :	*** [low = 9]
13-18 :	***************
19-24 :	************* [mean = 20.5 +/- 5.5]
25-30 :	********** [high = 29]

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

Physics 205B, spring semester 2019
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 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 image distance is a positive value when an image is formed on the on the right side of the lens by a real object. A negative number for image distance is when the image is formed to the left of the lens by a real object."

"I think I understand the difference between converging and diverging lenses. With diverging, you will always get a virtual image. With converging, if it is upright, it is virtual, and if it is inverted, it is real. This makes sense when thinking about eyes because they are converging lenses, so the image that we see is real, and it is displayed as inverted on the backs of our eyes (our retinas)."

"When looking at object and image distances, we can infer that if the object is located to the left of the focal lens, the image is real if light allows the image to moved to the right of the lens. If the image is virtual then that image is located to the left. We can also examine these relationships with an equation that relates object distance to image distance with the constant focal length."

"Thin lens equations can give us useful information like wether it's a converging or diverting lens depending on the f being positive or negative. Or if it's a real or virtual image depending on object distance or image distance is positive or negative."

"Converging lenses make inverted images, and all inverted images are real. Diverging lenses make upright, diminished images, and all upright images are virtual."

"Upright images make a positive magnification and inverted images make a negative magnification. For a camera to focus, the focal length remains fixed and distance is manipulated. For an eye to focus, the distance is constant and the focal length is manipulated. Myopia is nearsighted, which means you cannot see far objects and hyperopia is farsighted, which means you cannot see close objects."

"This was a cool one. I liked the example of eye problems, it made the lens stuff easier to understand. I was a little confused on "increasing image distance" for thin lenses of cameras until I read about how how eyes have a fixed image distance. It made sense because cameras can move their lenses to make an image closer, but you cant exactly move your eyes out of your head to do the same."

"The sum of the inverses of object distance and image distance is equal to the inverse of the lens focal length. Converging lenses have a positive focal length (produce real images) and diverging lenses have a negative focal length (produce virtual images). The magnification created by a lens is the ratio between image distance and object distance (the sign of this ratio is "flipped" for magnification)."

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'm having trouble still with ray drawings and light refraction which is making it difficult to solve problems like on the homework."

"I'm still working on understanding how to identify a real image versus a virtual image and the other parameters that go with it. I'll be spending time with a physics tutor this week to grasp this concept. I'm able to draw the rays, interpreting them is where I'm struggling."

"I am a little confused still on how to determine the difference between a real and virtual image."

"I am trying but I am not sure I understand how to read the ray drawings."

"It is hard for me to understand what focal length is. I understand that it can change the relationship between the object and image distance, but I do not understand how."

Identify the following thin lens parameters. (Only correct responses shown.)

Focal length: f [95%]
Magnification factor: m [95%]
Object distance: d_o [89%]
Object height: h_o [87%]
Image distance: d_i [95%]
Image height: h_i [92%]

For a simple camera, identify which parameter(s) must change or remain constant in order to focus on different distance objects.

Focal length: remains constant [49%]
Lens-to-film distance: changes [57%]

For a model eye, identify which parameter(s) must change or remain constant in order to focus on different distance objects.

Focal length: changes [59%]
Lens-to-retina distance: remains constant [57%]

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

Lens: converging [62%] (Only converging lenses can make inverted images.)
Image: real [57%] (All inverted images are real.)
Ray tracing: 1 [30%]

Lens: diverging [61%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [38%] (All upright images are virtual.)
Ray tracing: 6 [14%]

Lens: converging [35%] (Only converging lenses can make upright, enlarged images.)
Image: virtual [43%] (All upright images are virtual.)
Ray tracing: 4 [16%]

Lens: diverging [41%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [49%] (All upright images are virtual.)
Ray tracing: 7, 8, 9 or 10 [22%]

Lens: converging [41%] (Only converging lenses can make inverted images.)
Image: real [35%] (All inverted images are real, as the candle is upright, and the projected image is upside-down.)
Ray tracing: 1 [16%]

Lens: diverging [43%] (Only diverging lenses can make upright, diminished images.)
Image: virtual [46%] (All upright images are virtual.)
Ray tracing: 7, 8, 9 or 10 [19%]

Lens: converging [41%] (Only converging lenses can make upright, enlarged images.)
Image: virtual [30%] (All upright images are virtual.)
Ray tracing: 5 [19%]

Lens: converging [43%] (Only converging lenses can make inverted images.)
Image: real [32%] (All inverted images are real, as the slide is upside-down, making the projected image on the wall upright.)
Ray tracing: 2 [8%]

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 [81%]
Hyperopia: can see distant objects [81%]
Presbyopia: can see distant objects [76%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I'm completely lost about identifying the types of lenses and and if the image is real and I have no idea what the ray tracing number is."

"Please make this make more sense."

"I am pretty lost on how to tell whether things are seen through a converging/diverging lens."

"I'm still confused on real versus virtual images."

"Is text on a page considered real or virtual?" (The text on the page is an object. If you are looking at it with your naked eye, it will form a real image on the retina on the back of your eye.)

"I didn't really find anything confusing about the reading, but I think it would be beneficial to do some problems with the thin-lens equation to get a better understanding of it."

"This section seemed pretty clear and easy to understand, but I was confused when you stated that a camera initially focused on a distant object must move its lens outwards in order to focus on a nearby object. Does that mean that the lens gets smaller when it needs to see an object nearby?" (The lens remains the same size/shape, but the lens move outwards from its housing (increasing the image distance d_i as the object distance d_o decreases.)

"Since each of these vision defects are caused by an abnormal curvature of the eye, how does the curature change as say your vision gets worse?"