20200203

Online reading assignment: polarization

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 re-reading textbook chapters and reviewing presentations on polarization.


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.
"In order for TIR to take place, two things must take place: the index of refraction for the first surface must be greater than the second, and the angle incident angle is less than the critical angle."

"Horizontal and vertical antennae didn't make sense to me at first, but after seeing a visual drawing of them, I understand how waves can be transmitted and received in certain directions, but also have dead zones in specific areas."

"A vertical antenna can send messages to other vertical antennas, and has a blind spot on the top and bottom."

"The fencepost model describes how light polarized in a specific direction can pass through a polarizer. Malus's law allows us to calculate how much polarized light passes through a polarizer."

"With polarized light, if the transmission axis of polarizer is perpendicular, all light is blocked. Light with polarization parallel to the transmission axis passes."

"How polarizing sunglasses work. All the molecular antennas have their own direction of polarization in the sunglasses so only half of unpolarized light gets through polarized sunglasses. I also liked learning about liquid crystal displays and the polarization of calculator displays."

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 think I understand the theory behind polarization but concepts are new and a little hard to wrap my head around."

"Having issues visualizing Malus' Law."

"I need more practice on angles other than 90° and 0° or 180°."

"I am still having a hard time grasping Malus' law and I am confused about about how polarized light and the transmission axis of a polarizer works."

"When light passes through multiple polarizers it gets more confusing."

"Honestly it all seemed overwhelming and confusing. if the basics are covered I am pretty sure I'll understand it."

This is an ideal polarizer, where exactly one-half of unpolarized light passes through.  Realistically less than half of unpolarized light will pass through a polarizer, due to absorption and scattering.
How much unpolarized light is transmitted through an ideal polarizer?
0%.  * [1]
50%.  ********************************** [34]
100%.  * [1]
(Unsure/guessing/lost/help!)  * [1]

Unpolarized light shines through two ideal polarizing sheets, that have their transmission axes aligned at right angles to each other. How much of the original intensity is transmitted through these two sheets?
0%.  ********************* [21]
50%.  ****** [6]
100%.  ****** [6]
(Unsure/guessing/lost/help!)  **** [4]

Note that whatever its orientation, one-half of the original background unpolarized light always passes through the second polarizer, whether the second polarizer transmits or blocks light that passed through the first polarizer.
Unpolarized light is projected through the first (smaller) polarizer. If the transmission axis of this first polarizer is horizontal, then one-half of the unpolarized light will pass through, and the light that passes through is now horizontally polarized.

When the light that passed through the first polarizer is now completely blocked by the second polarizer, the transmission axis of the second polarizer is:

horizontal.  *** [3]
vertical.  ************************ [24]
diagonal, upper left to lower right.  * [1]
diagonal, lower left to upper right.  *** [3]
(Unsure/guessing/lost/help!)  ****** [6]

Polarizing sunglasses are typically manufactured with a vertical transmission axis (to filter out horizontally polarized glare while fishing or driving).

Light from the screen of the iPad (in portrait mode) is:

horizontally polarized.  ******************* [19]
vertically polarized.  *************** [15]
diagonally (upper left to lower right) polarized.  [0]
diagonally (lower left to upper right) polarized.  [0]
unpolarized.  [0]
(Unsure/guessing/lost/help!)  *** [3]

Consider a Nexus 4 smartphone (again, held in portrait mode), and polarizing sunglasses (with a vertical transmission axis).

Light from the screen of the Nexus 4 is:

horizontally polarized.  ***** [5]
vertically polarized.  ********** [10]
diagonally (upper left to lower right) polarized.  *** [3]
diagonally (lower left to upper right) polarized.  ************ [12]
unpolarized.  *** [3]
(Unsure/guessing/lost/help!)  **** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Please review answers to above questions."

"I think I need some clarification on the difference between polarized and unpolarized light in class if possible."

"Is diagonally polarized light a thing?" (Yes, definitely.)

"Why do screen manufacturers polarize screens in different ways? Why wouldn't there be an industry standard?"

"Does unpolarized light correspond to bright light? Can polarized light be as bright as unpolarized?" (Yes. Glare off of water or ice is mostly polarized, but polarizing sunglasses can help cut that down.)

"Book is here. Book is unread." (An unread book is a dead book.)

"Have you been to Pismo Preserve yet? The trails were really nice this weekend." (Not yet. #fomo.)

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