20170123

Online reading assignment: electromagnetic waves, reflection and refraction

Physics 205B, spring semester 2017
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 electromagnetic waves and redirecting light (reflection and refraction), along with advice from students from the previous semester, and videos on the flipped class mode of instruction used in this course.

To convince yourself that the frequency of the wave remains constant in either material, try this with a friend--when a crest appears from the left edge of the screen, say 'in.'  When a crest disappears at the right edge of the screen, have your friend say 'out.'

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.
"The difference between refraction (light passing through) and reflection (light bouncing off of). I understood how a higher n value corresponded to a slower movement of light through that particular medium."

"That visible light is only a tiny portion of the electromagnetic spectrum, and has some interesting properties as it passes through media. Indices of refraction are a measure of how fast or slow light travels through a media, and can bend when going from one medium to the next."

"That a faster light speed means that the refraction index will be lower, and vice versa."

"When light waves hit different media, it will speed up or slow down."

"The electromagnetic spectrum represents all types of light from low frequency to a high frequency. However, the human eye can only detect a small portion of this spectrum, called visible light."

"The reason why light waves become slower is because it was due to the change in the medium. The light waves do not covert to other types of electromagnetic radiation waves as one may assume, they are the same waves with the same frequency, but just at different speed because of the new medium, and because the frequency does not change it is still considered visible light."

"Honestly, I am still awaiting my book to come, so I did not read the textbook assigned pages."

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 just find it strange that mathematically wavelength equals speed over frequency, but if one were to rearrange the variables it would not necessarily be true, because wavelength is dependent on the other parameters (and not the other way around)."

"Remembering how the light is supposed to bend when going from fast-to-slow and vice versa."

"I need a little bit of practice regarding the refraction of light, I just need to do a few problems and I'll be solid."

"How to find wavelength and speed based on just knowing the index of refraction."

"The hierarchy of the wave parameters. Specifically, I don't understand what it means to be independent of the source or medium."

"Refraction, when it comes to the angles and what is meant by a larger angle with a lower index of refraction for a medium and a smaller angle with a higher index refraction for a medium."

Consider light traveling either through air (nair = 1.0) or through water (nwater = 1.33). Light travels with the faster speed through:
air.  ********************** [22]
water.  * [1]
(There is a tie.)  [0]
(Unsure/guessing/lost/help!)  [0]

A ray of light has an incident angle of 60° in air, and a transmitted angle of 36° in plastic. Determine what happens to each of the following parameters as the light passes from air into plastic.
(Only correct responses shown.)
speed v: decreases [87%]
frequency f: remains constant [74%]
wavelength λ: decreases [57%]

For the above example of light incident in air being transmitted into plastic, __________ has the greater index of refraction.
air.  **** [4]
plastic.  **************** [16]
(There is a tie.)  [1]
(Unsure/guessing/lost/help!)  ** [2]

A ray of light has an incident angle of 20° in plastic, and a transmitted angle of 29° in air. Determine what happens to each of the following parameters as the light passes from plastic into air.
(Only correct responses shown.)
speed v: increases [91%]
frequency f: remains constant [74%]
wavelength λ: increases [52%]

For the above example of light incident in plastic being transmitted into air, __________ has the greater index of refraction.
air.  ******************* [19]
plastic.  * [1]
(There is a tie.)  * [1]
(Unsure/guessing/lost/help!)  ** [2]

State your preference for denoting the inverse sine operation.
Arcsin.  [0]
sin-1.  ********************** [22]
(No preference.)  * [1]
(Unsure/guessing/lost/help!)  [0]


Explain what is different about homework in a flipped class.
"Homework in a flipped class takes place before and after class time, it is used to prepare the information so a student can use class time to really clarify concepts."

"The lectures are available before the class starts and directly pertain to the homework. This allows students to read the lecture ahead of time and ask questions in class they may have about homework."

"Homework is done more as an in-class activity, where students can benefit more from assistance from the teacher and embedded tutor."

"I think it really helps people learn more deeply. If you read about the lesson and can come to class with questions, it can really improve your experience and your professor can help you learn the way you learn. You also have more control over how you're learning new information."

"Homework is to go over the lecture before the class and also to check knowledge after the class."

"The questions are more complex."

"Homework consists of reviewing the lecture so that topics can be discussed in class. The lecture is more hands on with practice problems and group discussion versus just lecture slides."

Describe where/when most student learning occurs in a flipped class.
"Some students do better listening, some students do better observing, so the most learning can happen before class or during class. But the bulk of information access happens before the actual lecture."

"Most of the learning in the flipped class comes in the classroom. The students learn before class and have a general idea and then once they get to class, they can ask specific questions and no one gets bored or left behind."

Pick one piece of student advice from the previous semester, and discuss why you agree (or disagree) with it.
"'Don't read the book, it's useless.' I get where this student is coming from. My use of it was relatively low compared to my other classes, admittedly. However, I would not call it useless. There were several instances in which I made a connection I would have never made otherwise, about this or that topic, as a result of reading the text."

"'Going to the tutor was the only reason I am passing this class!' This is a great piece of advice and one that helped me achieve success last semester."

"'Doing the homework and the things before class is useful.' Doing the homework every day. Even though it can become tedious, it makes the rest of the class much less stressful."

"'Having the blog handy is also very helpful.' Like in a flipped class it can really help you to come to class with a little bit of knowledge of what you'll be working on."

"'What helped me study was doing the example problems given to us before an exam, that way I can find out what I need to work on and study that harder.' I agree with this piece of advice because a big portion of this class is knowing how to attack problems. By doing repititions of the hard problems I'm stuck on, this will prepare me best for the tests."

"'It does not help to procrastinate, it is important to keep up with homework and lab, they really help.' I agree with it completely because then you are wasting the professor's and your time if you are not willing to put in the time to do the work."

"'Breathe.' I shouldn't allow myself to get so stressed. I just need to stay on top of the online homework and go to tutoring if needed. Not procrastinating will help me avoid getting stressed."

"'P-dog's blog and worked-out problems online are probably the most helpful besides just reading the chapters.' Most if not all of the material coverd in class comes from the blog. It's name is very true, boring but important. I really enjoyed what I looked at last semester and sadly it took me a couple weeks to understand the true importance about reading the blog. So yes, read the blog and you will be ready for any questions that you might have."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Looking forward to an enlightening semester P-dog!"

"My plan in the class is to get an 'A' without having to take the final. How many people have done so in the past?" (Usually there is at most one or two people able to do that each semester.)

"I am confused why the spectrum of light visible to the human eye is so limited. Why can't we detect other electromagnetic waves?" (Most of the electromagnetic radiation emitted from the sun that is able to penetrate Earth's atmosphere is in the visible light spectrum; if we could only detect other forms of electromagnetic radiation, it would be pretty dark all day and night.)

"What is it about different materials that cause a different index of refraction? Why does light go through some things more slowly than others?" (It's mainly the behavior of electrons in the (transparent) material, which absorb and then re-transmit light to each other like a bucket brigade. Denser materials will typically have more electrons and thus slower transfer speeds for passing light from electron to electron.)

"I am hoping to finish all the homework tomorrow before class at 12:30 PM." (Sorry, but the online homework deadline doesn't work that way.)

"I took Phys 205A in Fall 2015, so it's been a year since I've taken physics but I'm glad to be back in your class again!"

"I used to think I couldn't do physics, because I had never taken it and am not really good with the maths, but you made me feel a lot more confident after last semester; thank you for all your hard work P-dog. Im pretty sure I can do well in this class, too."

"What do you like to do on your free time?" (Mrs. P-dog and I live the #vanlife during summers, going hiking, backpacking, and peakbagging.)

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