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 optical instruments and interference.
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.
"Phase differences and path length differences can lead to constructive interference (where the waves and troughs are in sync) or destructive interference (where the waves and troughs run into one another and cancel each other out)."
"Both microscope and telescopes, also have a good understanding on constructive and destructive sound waves as well."
"Microscopes and telescopes are very similar in their construction, the main difference being that a telescope's objective lens focuses objects that are as far as infinity (whose rays could be basically parallel) to create a real image onto the focal point of the eyepiece."
"A converging microscope objective lens uses a ray tracing where the object is just outside the objective lens' focal point to produce an enlarged, inverted, real image, which is placed at the eyepiece's focal point."
"A microscope is a short tube that holds two separate lens apart from each other. In which light is passing through two different lenses, consecutively. The first lens picks up an object which in turn creates a real image, this image then becomes the object for the second lens for the eyepiece in which the person looking through the eyepiece can now see magnified."
"Microscopes and telescopes pretty much have the same structure of eyepieces, objective lens, and a tube between each. When the objects rays go through the objective then it'll form a real image where it will be at the focal point of the eyepiece for maximum angular magnification. Sound waves can either be constructive (same troughs and peaks) or destructive (opposing troughs and peaks) depending on their phase and path length differences."
"I hate that this asks what I understand--I don't feel as though I understand any of this."
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 still am a little confused about modeling microscopes and telescopes with the ray tracing diagrams. How can you tell exactly how big the intermedia real image is going to be?"
"Really hard time understanding the microscope ray tracings. I am not understanding how the reversal of principal rays works."
"Ray tracings for both the microscope and the telescope confusing. I actually find the ray tracings in general to be confusing. Help."
"The two equations detailing angular magnification for a microscope and telescope."
"I don't completely understand why a microscope uses an objective lens with a short focal length and a telescope uses an objective lens with a long focal length. And is the first image produced by a telescope technically enlarged or diminished?"
"I am still really struggling with are the ray tracings. I know I need to take more time to practice these and just get additional help. But I can assure you that I will be taking more time to figure this stuff out."
"I'm not sure what is the differences between phase difference and path length difference."
Identify the type for each of these lenses. (Only correct responses shown.)
Microscope objective: converging [82%]
Microscope eyepiece: converging [72%]
Telescope objective: converging [74%]
Telescope eyepiece: converging [64%]
Identify the ray tracing for each of these lenses. (Only correct responses shown.)
Microscope objective: ray tracing 2 [56%]
Microscope eyepiece: ray tracing 3 (or 4) [51%]
Telescope objective: ray tracing 1 [26%]
Telescope eyepiece: ray tracing 3 (or 4) [49%]
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. ************************ [24] short; long. ******** [8] long; short. ***** [5] long; long. * [1] (Unsure/lost/guessing/help!) * [1]
A telescope should have a __________ focal length objective lens and a ___________ focal length eyepiece lens in order to maximize its angular magnification.
short; short. * [1] short; long. **** [4] long; short. ************************** [26] long; long. ***** [5] (Unsure/lost/guessing/help!) *** [3]
1: in phase sources; whole wavelength path difference; constructive [77%]
2: in phase sources; half wavelength path difference; destructive [51%]
3: in phase sources; whole wavelength path difference; constructive [54%]
4: out of phase sources; whole wavelength path difference; destructive [56%]
5: out of phase sources; half wavelength path difference; constructive [49%]
6: out of phase sources; whole wavelength path difference; destructive [59%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"A myopic person (nearsighted, can see near, but can't see far) due to defects in curvature of the eye, who as a result of aging develops presbyopia, loses the ability to accommodate and see nearby objects. Would you would need to prescribe separate diverging and converging lenses to correct for myopia and presbyopia?" (Yes--that person would need bifocals.)
"Is the first image produced by a telescope technically enlarged or diminished?" (With respect to the original object, the objective lens' image is real, inverted, and diminished. However, it then becomes a (small) object brought very close-up to the eyepiece than can be magnified.)
"What is N for the microscope equation?" (The nominal near point value, which is 25 cm.)
"Can we lecture more on the wavelength stuff in class?"
"I don't like ray tracings."
"I promise to spend more time on physics this week." (#squadgoals)
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