20140127

Online reading assignment: reflection and refraction

Physics 205B, spring semester 2014
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 a presentation on redirecting light (reflection and refraction).

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 that from one medium to another, electromagnetic waves will have the same frequency but the speed will change proportionally with the wavelength. I also understand the diagram regarding the changes in angles in to Snell's law."

"Although I already knew this from the spectroscopy in biology, I always find it interesting that visible light is only what we see but is included in the entire electromagnetic spectrum."

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 was confused on how to use the equation for light traveling through two different media."

"Can we please discuss Snell's Law in more detail in class? I want to understand what the practical applications are, and understand how to use and apply it."

"Although I'm not confused now, I know I will be as soon as I try to use the equations. The parameters for light I know I will mix up which are independent and which are dependent. Snell's law also confuses me a bit."

A ray of light travels through air (nair = 1.0), or through glass (nglass = 1.5). Light travels slower in:
 Air. *** [3] Glass. ********************************* [33] (There is a tie.) * [1] (Unsure/guessing/lost/help!) * [1]

A diagonal ray of light in air (nair = 1.0) is transmitted down into glass (nglass = 1.5). Explain using Snell's law why the incident angle in air (θi) is greater than the transmitted angle in glass (θt).
"I would say that the angle is smaller due to the very nature of Snell's Law. Since nglass is larger, the angle must be smaller so that nglass·sinθglass = nair·sinθair."

"I'm struggling with Snell's law."

What is your preference for denoting the inverse sine operation?
 Arcsin. ****** [6] Sin-1. **************************** [28] (No preference.) *** [3] (Unsure/guessing/lost/help!) * [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"After going over the online presentation, reading the textbook, and taking notes I feel that I understand the concepts but need to be shown how to apply the concepts to problems. Can we do some of that in class?" (Yes.)

"It's good to be back to another semester of the physical universe!" (But you never actually left the physical universe.)

"Could you explain in your words how the mirage phenomenon works?" (Wait until we discuss total internal reflection.)

"I was confused as to what makes some of the light on the electromagnetic spectrum not visible to the eye. What makes light visible to the eye?" (Crudely speaking, antennae of a given size are sensitive to light waves that have approximately the same wavelength. Large antennae transmit and receive long wavelength radio waves. Cellphones contain small antennae for shorter wavelength radio waves. For visible light, its very small wavelengths correspond to the electron bonds in certain proteins in your rod and cone cells. Receiving visible light causes these electron "antennae" to absorb energy which changes the structure of these proteins, and your rod and cone cells perceive the presence of these transformed proteins as "seeing" light.)