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 magnifiers and optical instruments.
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.
"For microscopes I understand that object 1 becomes image 1 for the objective and then image 1 becomes object 2 for the eyepiece. The same is true for telescopes."
"I got the similarities between telescopes and microscopes: the three basic components (objective lens, tube, eyepiece) and they both produce a real image that becomes object 2 for the eyepiece. Object 1 for a telescope is extremely far away, which differs from a microscope in that its rays hit it as essentially parallel rays."
"I understand the key differences between a microscope and telescope much better now."
"I understand that the angular size is not the actual size. I believe that the angular size is a measure of how big something "seems" from your viewpoint."
"The textbook reading was easy to understand and I get the basic principles and ideas presented on microscopes and telescopes. I also understand the section on angular magnification."
"I understand that the microscope and telescope lenses are all converging lenses. I understand that they differ in that the microscope should have short focal lengths while the telescope should have a short eyepiece focal length and long objective focal length. If these are as short and long as possible, given the instrument, this will optimize angular magnification."
"A magnifier (converging lens) doesn't really magnify by enlarging an object, but it puts the object into focus by putting in on the focal point. A higher angular size means a bigger object seen but to a near point for optimal focus. The final images of microscopes and telescopes are inverted images."
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 very confused. In all the pictures on the blog all the rays from the first lens converge on the focal point of the second lens so I'm unsure if I'm missing something."
I don't understand--how does a simple magnifier use a converging lens to form an upright image that is larger?"
"I am confused about whether the eyepiece creates an image 2 because it does not look like the lines ever intersect. This is like ray tracing 3 but it doesn't seem right that it will not create an image."
"I don't really understand how the microscope and telescope ray tracings produce an image because light rays hit the objective and produce real images but they fall on the focal point of the eyepiece (similar to ray tracing 3) making no image. I feel like the two should produce ray tracings like 4 or 5 (virtual, enlarged images) because that's what they do."
"From the reading in the textbook and the online presentation from the blog I am confused on the simple magnifier and the ray tracings associated with microscopes and telescopes."
"I am still confused with the ray tracings. I don't understand how to figure out which is which when it comes to microscopes eyepieces and telescopes in general."
"I'm getting confused with the telescope and microscope stuff. I'm confused when we start dealing with more than one lens."
"I am confused by the intermediate images formed and the how the images become the objects for the second lens."
"It was pretty clear and the presentation pictures were very helpful."
Identify the type for each of these lenses. (Only correct responses shown.)
Telescope objective: converging [84%]
Telescope eyepiece: converging [84%]
Microscope objective: converging [91%]
Microscope eyepiece: converging [81%]
Identify the ray tracing for each of these lenses. (Only correct responses shown.)
Telescope objective: ray tracing 1 [38%]
Telescope eyepiece: ray tracing 3 or 4 [47%]
Microscope objective: ray tracing 2 [56%]
Microscope eyepiece: ray tracing 3 or 4 [34%]
A (compound) microscope should have a __________ focal length objective lens and a ___________ focal length eyepiece lens in order to maximize its angular magnification.
short; short. ********************** [22] short; long. ******* [7] long; short. **** [4] long; long. [0] (Unsure/lost/guessing/help!) *** [3]
A telescope should have a __________ focal length objective lens and a ___________ focal length eyepiece lens in order to maximize its angular magnification.
short; short. [0] short; long. **** [4] long; short. *************************** [27] long; long. ** [2] (Unsure/lost/guessing/help!) *** [3]
Identify the tube/barrel length L definitions for these optical instruments. (Only correct responses shown.)
Microscope: distance from inside focal point to inside focal point [61%]
Telescope: distance from lens to lens [53%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I just need to see some stuff on microscopes and telescopes."
"We get to look at microscopes and telescopes in class? Ooo weee!!!"
"What will the ray tracings be like on the quiz?" (Like any of the ray tracings from the converging/diverging lens worksheet.)
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