## 20170130

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 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.
"That light will travel through a polarizer that has the same orientation as the waves of light. If a polarizer has a vertical orientation, vertical waves (or vertical components of waves) will pass through while horizontal waves will not."

"The total internal reflection (TIR) flowchart is a visual concept that I was able to grasp quickly. You can determine if Snell's law fails (or not); or you can calculate the critical angle θc for the first medium (n1) when θ2 in the second medium (n2) has a 90° angle. If θc is less than θ1 we can say that there is TIR, but if θc is greater than θ1, then there will be transmission and reflection."

"Polarized light is not polarized when you are looking directly at it, but when looking after it has been side-scattered it is polarized in some way."

"I better understand the concept of polarization now with the help of some practice. It still takes a while for me to process and visualize it in specific problems."

"Vertical antennas must have vertical receiving antennas. Horizontal antennas must have horizontal receiving antennas. Any light parallel to a polarizer will pass through, but anything perpendicular will be blocked."

"The part that did make sense to me was the section of the transverse waves. The waves or the oscillations of the rope can go in any direction, and those waves that have been created have a similarity to that of the polarization of the transverse waves."

"For best reception, the orientations of the source antenna and receiving antenna should match. Malus' law determines the intensity of light passing through a polirozation based on angle of the incidence light vs transmission axis of the polarizer."

"There are polarizers to prevent differently polarized light from going through. The amount of light that gets through depends on the angle that the polarizer is at."

"Polarized light will only pass through if it is parallel to its filter. Perpendicular light will not be able to pass through a filter."

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.
"The drawings we did in class with the compass of how the radio waves with certain transverse polarizations that go N-S or E-W, etc.. When we did the in class worksheet it started to make more sense but that only was because I was able to talk it out and visualize out loud."

"Trying to find the vertical/horizontal polarizations of the filters in front of the display screens, it's just a little hard to mentally picture it."

"I need much more help on polarized and unpolarized light in regards to dipole antennae transmissions and polarization by scattering. I think that if I did more problems it would help me understand much better."

"How horizontal and vertical polarized light is generated."

"Malus' law. I would like to go over an example of it in class because I only kind of understood it from the textbook and the blog."

How much unpolarized light is transmitted through an ideal polarizer?
 0%. ***** [5] 50%. ******************* [19] 100%. *** [3] (Unsure/guessing/lost/help!) **** [4]

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%. ******************* [19] 50%. **** [4] 100%. ****** [6] (Unsure/guessing/lost/help!) ** [2]

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. * [1] vertical. ********************** [22] diagonal, upper left to lower right. * [1] diagonal, lower left to upper right. ** [2] (Unsure/guessing/lost/help!) ***** [5]

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. ***************** [17] vertically polarized. ********** [10] diagonally (upper left to lower right) polarized. [0] diagonally (lower left to upper right) polarized. [0] unpolarized. * [1] (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. ****** [6] diagonally (lower left to upper right) polarized. ********* [9] unpolarized. [0] (Unsure/guessing/lost/help!) * [1]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"In the last class, I was confused on the example where we held our pens in a perpendicular direction towards the pen you were holding up. Does that allow for the best possible signal when you point in the perpendicular direction to the antenna?" (Yes.)

"So if you don't want any sunlight to mess with your eyes you have to buy horizontally polarized glasses and then buy another pair of vertically polarized?" (Yes, but you wouldn't want to wear both of them at the same time. But because most reflective surfaces are horizontal (lakes, oceans, and wet roads), then you would mostly need vertically polarized sunglasses to block out that glare.)

"I am a little confused about unpolarized light. So since it goes in all directions, if there is a filter, then would only half of the light come through since the ones perpendicular to the filter will be blocked?" (Yes.)

""An example on when the transmission axis of the polarizer is on an arbitrary angle with respect to the polarization of the incident light would be helpful."

"I don't really understand what happens when two filters are stacked on top of the other. If the two filters are parallel would they act the same as one filter?" (Yes. But if they are at arbitrary orientations, then take each filter one at a time--let light pass through one, and see how much light gets through; then let light pass through the next, and see how much of that light gets through.)

"An example on when the transmission axis of the polarizer is on an arbitrary angle with respect to the polarization of the incident light would be helpful."