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.
"The direction of disturbances, perpendicular to the direction of the wave, determine the polarization of the wave. An example of polarized light source is an antenna."
"When atoms and electrons, sources of light, vibrate in different directions, they generate unpolarized light. In contrast with antennas, electrons have to move up and down the length."
"Waves that are linearly polarized can only pass through openings that are parallel to the direction of the rope vibrations. A polarizing material is called a polarizer."
"I felt like I really grasped the idea of the fencepost models we were given and how when unpolarized light is incident on a polarizer, only the light parallel to the polarizer will pass through.The light that passes through will have a polarization direction that matches the transmission of the polarizer."
"I understood that all light will pass through a polarizer if the transmission axis and polarization of the incident light are parallel. In contrast, if the polarization of the transmission axis and incident light are perpendicular, no light will pass through."
"Light that is perpendicular to a polarizer is not transmitted. The intensity of light that passes through a polarizer is related to the angle of the polarizer to the transmission axis of the light. The intensity of light transmitted is equal to the intensity of light entering the polarizer multiplied by the square of the cosine of the angle of the polarizer."
"Malus' law is a way to determine the intensity of polarized light after it goes through a polarizer and is filtered. Cos2θ of the unpolarized light going through a polarizer will give you the new intensity of the polarized light."
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 am confused as to why east-west oriented antennae are best transmitted north-south. What causes this?"
"I'm not quite understanding how it is that electrons can move side to side along a horizontal antenna."
"I find it confusing when unpolarized light passes through several stacked polarizers ( how the polarization of the polarizers affects the light)."
"Unpolarized light could be a little confusing. I also found some of the questions a bit confusing."
"I do not fully understand how to structure information about polarizers to solve questions about the intensity of light. I would benefit from examples on how to use Malus' law."
"I don't quite understand the LCD screen section. I would like to understand more about how voltage works. It makes sense to me that light is one type of electromagnetic wave but I am confused about how it relates to the positive and negative charges on the transparent electrodes sandwiching the liquid crystal. I also don't quite understand how the liquid crystal works and if it is related to solid crystal."
0%. **** [4] 50%. *********************** [23] 100%. ***** [5] (Unsure/guessing/lost/help!) ***** [5]
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%. ******************** [20] 50%. ******** [8] 100%. **** [4] (Unsure/guessing/lost/help!) ***** [5]
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. **************** [26] diagonal, upper left to lower right. *** [3] diagonal, lower left to upper right. [0] (Unsure/guessing/lost/help!) ***** [5]
Light from the screen of the iPad (in portrait mode) is:
horizontally polarized. ******************* [19] vertically polarized. ********** [10] diagonally (upper left to lower right) polarized. * [1] diagonally (lower left to upper right) polarized. ** [2] unpolarized. [0] (Unsure/guessing/lost/help!) ***** [5]
Light from the screen of the Nexus 4 is:
horizontally polarized. ******* [7] vertically polarized. ********* [9] diagonally (upper left to lower right) polarized. ***** [5] diagonally (lower left to upper right) polarized. [11] unpolarized. [0] (Unsure/guessing/lost/help!) ***** [5]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This section is making sense to me and I find it very interesting because I've always wondered what polarized sunglasses did. I think all of the concepts make sense to me so far but I do have a couple questions about polarized light. For one, I am having a hard time understanding the energy of light and basically how it is created. It just seems weird to me how antenna's shoot electrons up and down to create a wave out of thin air? What are these waves made of? How do they keep energy and are able to travel so far?"
"I like this section but I wish there was more explanation of how light waves are formed, and what they are. I understand the concepts but it would be cool to get deeper understanding of how it all works. For example if I wanted to create and antenna and start sending out waves I would have no idea where to start." (Wait until we get through electromagnetism, as light waves are just oscillating electromagnetic fields.)
"What makes a material capable of polarizing light?" (Something that looks like fencepost on the scale of light wavelengths. A set of parallel metal rods will polarize radio waves, while a sheet with long, parallel polyvinyl alcohol chains will polarize visible light.)
"If something is polarized, that means light only transmits in a single direction? If sunglasses are polarized, that means that only single direction of light can transmit through?" (Yes.)
"I am confused about the two polarizer filters lined up and how much unpolarized light is able to get through. If only 50% gets in through the first one and the second filter is lined up on the same axis then would 50% be the final amount that gets through and if the second filter is lined up on a perpendicular axis it would be 0%?"
"Could you go into these sunglasses examples especially the one with the Nexus smartphone?"
"I'm kind of struggling on this subject."
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