Physics quiz archive: electromagnetic waves, polarization, reflection/refraction

Physics 205B Quiz 1, spring semester 2020
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz01PxP7



Sections 30882, 30883 results

0- 6 :	* [low = 6]
7-12 :	**
13-18 :	*********
19-24 :	*********** [mean = 21.9 +/- 5.9]
25-30 :	************ [high = 30]

GIF animation: Today is Laser Täg

Physics 205B, spring semester 2020
Cuesta College, San Luis Obispo, CA


"Today is Laser Täg"
flic.kr/p/2ioGjcr
Waifer X

Online reading assignment: total internal reflection, 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 reading textbook chapters and previewing presentations on total internal reflection and 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.

"As the angle of incidence increases, so does the angle of refraction. I also understand that when the angle of incidence exceeds the critical angle there is no refracted light (saw this in lab), resulting in total internal reflection."

"Total reflection was the reason why we couldn't solve one of the problems on the in-class worksheet. In our case the refraction from water to air went past the critical angle which meant that the light was only reflected back into the water. "

"I understand why we received a 'domain error' when calculating the transmitted light ray from the previous class' worksheet. This was due to total internal reflection, which meant that no light was transmitted into the lower refractive index material, but instead only reflected back into the higher refractive index material. TIR occurs when the incident is greater than the critical angle."

"Total internal reflection is when light is in a higher refraction material index making n₁ higher, and slower for light to move through. If the incident angle is greater then the critical angle, it is reflected back into the higher index material."

"I really understood and actually kind of enjoyed reading about total internal reflection. It was interesting to see how many aspects of life the concept applies to, including diamonds and optical fibers in the medical field. The critical angle was also a part of the reading that I was able to comprehend and even complete some problems on."

"Fiber optics is a demonstration of total internal reflection that we use in our every day lives. Light is shone through a fiber and reflects with little loss of light all the way to the other end. Fiber optics is used in computers, cable and much more to transmit data at high speeds."

"Light can also be transmitted vertically or horizontally by an antennae, which is a polarized light source, where the receiving antennae should be positioned the same as the transmitting one."

"Radio waves transmitted from vertical antennas release vertical radio waves--which are read by accepting vertical antennas. The same goes for horizontal radio waves and antennas."

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 found it confusing how it is helpful to know about the critical angle. As well, I didn't understand when you know there is a critical angle. Is it just when you use Snell's law and the equation can't be solved?"

"I'm confused about how optic fibers work in an endoscope."

"Optic fibers--does it contain mirrors to reflect light? I was confused as why the light does not simply escape through the sides of the object."

"Polarization. Basic review and explanation is needed."

"I do not understand polarized light waves and how they work. If they use transverse waves, then it can move in multiple directions. have a hard time imagining what a vertical antenna does."

If the incident angle of a light ray is less than the critical angle, the light ray will be:

reflected.	[0]
transmitted.	*************** [16]
(Both of the above choices.)	************ [12]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

If the incident angle of a light ray is greater than the critical angle, the light ray will be:

reflected.	*************************** [27]
transmitted.	[0]
(Both of the above choices.)	[0]
(Neither of the above choices.)	* [1]
(Unsure/guessing/lost/help!)	*** [3]

Total internal reflection is possible when a light ray in a __________ medium hits a boundary with a __________ medium.

faster; slower.	********** [10]
slower; faster.	************************ [14]
(Both of the above choices.)	[0]
(Unsure/guessing/lost/help!)	******* [7]

A vertical antenna will emit __________ polarized light.

horizontally.	[0]
vertically.	*************************** [27]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

Horizontally polarized light can be received by a _________ antenna.

horizontal.	************************** [26]
vertical.	[0]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Is total internal reflection what is happening when Snell's law cannot be calculated in our calculators and it gives an 'error' reading?" (Yes.)

"May we review when to use Snell's law from Monday versus the law of reflection from today's reading (critical angles)?"

"Why does total internal reflection only occur when light moves from slower to faster medium?"

"Can you please recap on polarized light/antennas? Thank you!"

"I would like to go over the different symbols and how to use them."

"Cool but challenging."

"So far the topics for this semester seem very independent and that they don't really build on each other?"

Online reading assignment: electromagnetic waves, reflection and refraction

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 reading textbook chapters and previewing presentations on electromagnetic waves and redirecting light (reflection and refraction), along with advice from students from the previous semester.


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 concept of the electromagnetic spectrum and the difference between visible light and other types of radiation like infrared."

"Electromagnetic radiation is a large spectrum and visible light is the only wavelength range that we can perceive."

"Speed and frequency are independent parameters, while wavelength is dependent and therefor set by λ = v/f. Light reflection is light bouncing off a surface, refraction is light bending through an object."

"Light traveling through any other transparent source than vacuum will experience a slower speed, and with that slower speed, the index of refraction will be greater than one."

"Light can be refracted as it passes through different materials giving it bending like an illusion. According to Snell's law n₁·sinθ₁ = n₂·sinθ₂ where n₁ and n₂ are the indices of refraction and θ₁ and θ₂ are the incident and refracted angles."

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 don't understand why if you change to a denser medium that wavelength and velocity decreases when I think it should increase to travel through the medium."

"I am having a hard time finding or understanding the relationships between the speed, frequency, and wavelength of light as it passes from one medium to the next."

"I didn't really understand index of refraction. I understand how to use it not why we use it."

"How to apply Snell's law. A better description of the sayings 'fast-to-slow bends toward the normal' and 'slow-to-fast bends away from normal' is needed."

"I was most confused by the definition of the 'normal.' I didn't understand where the term came from or was in reference to."

"Snell's law seems pretty confusing, but I'm sure if you go over it in class that I'll be solid."

"Some of the equations and how to use them properly."

"Need to review most of the signs and symbols."

Consider light traveling either through air (n_air = 1.0) or through water (n_water = 1.33). Light travels with the faster speed through:

air.	************************************ [36]
water.	* [1]
(There is a tie.)	[0]
(Unsure/guessing/lost/help!)	* [1]

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 [79%]
frequency f: remains constant [47%]
wavelength λ: decreases [42%]

For the above example of light incident in air being transmitted into plastic, __________ has the greater index of refraction.

air.	[0]
plastic.	********************************** [36]
(There is a tie.)	[0]
(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 [66%]
frequency f: remains constant [58%]
wavelength λ: increases [40%]

For the above example of light incident in plastic being transmitted into air, __________ has the greater index of refraction.

air.	**************************** [28]
plastic.	***** [5]
(There is a tie.)	[1]
(Unsure/guessing/lost/help!)	**** [4]

State your preference for denoting the inverse sine operation.

Arcsin.	[0]
sin–1.	******************************** [32]
(No preference.)	**** [4]
(Unsure/guessing/lost/help!)	** [2]

Pick one piece of student advice from the previous semester, and discuss why you agree (or disagree) with it.

"'A piece of advice I would give myself is to get help from a tutor immediately because you can't teach yourself how to do it," is a statement I inherently disagree with given my experience in this previous semester. Although at times some concepts may be difficult to grasp, with some in class review and at home practice at problems, the material is generally understandable on my own or with some light guidance."

"'I would tell myself that if you never miss a lab or lecture there's a very good chance that you'll get an 'A' in this class. I would also tell myself to spend a good amount of time trying to understand the reading assignments on waiferx.blogspot.com because they're super-informative and helpful with understanding the material.' After taking Physics 205A with Dr. Len last semester, I know completing the homework and reading assignments are EXTREMELY important. After gaining points from the smaller assignments, I was able to receive a low grade on the final and still earn an 'A'."

"'Just stay on top of your assignments, it's easy points. Also try to focus on things that aren't very clear to you the most because if you have a grasp on other concepts then it's pretty straightforward, considering physics is somewhat logic based. Also for the midterms just study what you messed up on the quizzes and grind those concepts into your skull. Other than that, easy cash. I should not procrastinate to study when an exam is coming up.' I agree with it because this is exactly how I learned and survived my with my A last semester."

"'Make sure to do all the online homework and reading assignments because those points rack up.' I would chose this statement as it is something I failed to do successfully that cost me the higher grade."

"'Define equation variables before the exams.' Even if the problems on the tests and quizzes from last semester didn't make much sense at first glance, they could have still been done correctly if you had a complete understanding of the equations and their variables."

"'I would advise myself to do all the homework assignments to maximize my points in those categories and give myself a chance of skipping the final altogether.' I agree with the statement above because I took Physics 205A last semester with P-dog and I know that getting an 'A' is possible as long as I keep up with all the homework, going to class, and doing well on the quizzes. This semester I would like to not have to take the final, therefore I'm going to be reaching for that goal all semester long."

"'Stay on top of the assignments and don't forget them.' Last semester for about the first few months I was forgetting to do the HW and Reading assignments and as a result, I left a lot of free/easy points on the table. But I changed that towards the end of the semester."

"'Don't give up and keep moving forward! Read the book from the start of the semester!' was good reminder that you always have to take one step at a time and the only direction you can go is forward by studying and doing homework. I agree with this, because as long as you keep putting in the time, your understanding of the concepts will only grow."

"'Spend more time going back through notes/examples from class.' This is because this piece of advice is what I do to study for most of my classes. I believe this helps me understand the material the most efficient way possible."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"It seems as though we're hitting the ground running this semester. So far I am intimidated by the optics topics but am hoping I will feel better about them after lecture."

"Is the difficulty of the homework, quizzes and worksheets similar to the exam difficulty?" (The homework and worksheets are adapted from actual quiz questions; but we will also assign past exam questions for you to study later this semester.)

"Please go over this stuff!"

"Looking forward to this semester! So far it seems like the concepts are going to be super-different!"

"Great to be back!"

"Getting my book soon."

Physics midterm question: comparing indices of refraction

Physics 205B Midterm 1, spring semester 2019
Cuesta College, San Luis Obispo, CA

Light in air with an incident angle of 19.0° is transmitted into acetone at an angle of 13.9°. Light in air with an incident angle of 44.0° is transmitted into turpentine at an angle of 28.2°. Show that the index of refraction of acetone is less than the index of turpentine. Explain your reasoning using the properties of light and refraction.

Solution and grading rubric:

• p:
  Correct. Uses Snell's law to solve for and compare the numerical values for the indices of refraction of acetone versus turpentine.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying Snell's law, angles, and/or indices of refraction.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying Snell's law, angles, and/or indices of refraction.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01Ft6G
p: 41 students
r: 0 students
t: 0 students
v: 1 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1348):

Physics quiz archive: electromagnetic waves, polarization, reflection/refraction

Physics 205B Quiz 1, spring semester 2019
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz01aN7u




Sections 30882, 30883 results

0- 6 :	* [low = 3]
7-12 :	****
13-18 :	*******
19-24 :	***************** [mean = 20.8 +/- 5.7]
25-30 :	******** [high = 27]

Online reading assignment: total internal reflection, polarization

Physics 205B, spring semester 2019
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 total internal reflection and 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.

"I think I'm starting to really understand Snell's law."

"If the incident angle results in an transmitted angle greater than 90°, then all of of the light is reflected back and you have total internal reflection (TIR). If the incident angle results in a transmitted angle that is 90° from the normal, then the incident angle is called the critical angle."

"During total internal reflection, where the incident angle in the medium with higher n is larger than the critical angle, light wouldn't be transmitted to the medium with smaller n. In this case, Snell's law doesn't apply."

"One of the things I understood was the difference between a polarized light source and an unpolarized light source. A polarized light source vibrates organized (up-and-down, side-to-side, diagonal-to-diagonal). An unpolarized light source vibrates randomly."

"If unpolarized horizontal and vertical rays pass through a polarizer, only the parellel rays will pass through the transmission axis and the perpendicular rays will be blocked."

"Sorry P-dog, but I am swamped."

"I honestly just did not get to this yet."

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 Snells law formula did kind of confuse me. I get a little confused with which parts go up when others go down."

"I found total internal reflection to be quite confusing. I had time figuring out what exactly the critical angle meant and how it tied into each scenario. In the homework I also had trouble with the 'plug-and-chug' questions and relating the index of refraction to a wavelength etc. and finding that the frequencies were equal to each other."

"What I don't understand is how the critical angle idea works. Why there? Why does it work?"

"The idea of a critical angle confused me a little bit. I may just have to go back and read it a little bit closer or read about it more in the textbook."

"What I found confusing from the reading was the application part of total internal reflection. I understand the part about the diamond and how it is cut a certain way to reach TIR. I do not understand about optical fiber and the see snake and how they are able to reach TIR."

"I don't understand the difference between horizontal polorized light and vertical polorized light. Also, I am not sure when transmitted if it's vertical or horizontal polarization from the antenna."

"Sound waves cannot become polarized because they travel longitudinally? I do not quite understand what this means. I think that it means the wave moves forward and backwards along a path outward from the source, but it is difficult for me to visualize. Also, light can be polarized because it is transverse? I would like to understand these concepts with more clarity."

"I didn't understand the section about polarizers and the fence post model. A discussion in class about this would be beneficial."

"I'm not confused about anything in particular."

If the incident angle of a light ray is less than the critical angle, the light ray will be:

reflected.	*** [3]
transmitted.	*********************** [23]
(Both of the above choices.)	******** [8]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

If the incident angle of a light ray is greater than the critical angle, the light ray will be:

reflected.	******************************* [31]
transmitted.	** [2]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	* [1]
(Unsure/guessing/lost/help!)	** [2]

Total internal reflection is possible when a light ray in a __________ medium hits a boundary with a __________ medium.

faster; slower.	********* [9]
slower; faster.	****************** [18]
(Both of the above choices.)	*** [3]
(Unsure/guessing/lost/help!)	******* [7]

A vertical antenna will emit __________ polarized light.

horizontally.	******* [7]
vertically.	************************ [24]
(Both of the above choices.)	[0]
(Neither of the above choices.)	* [1]
(Unsure/guessing/lost/help!)	***** [5]

Horizontally polarized light can be received by a _________ antenna.

horizontal.	*********************** [23]
vertical.	********* [9]
(Both of the above choices.)	* [1]
(Neither of the above choices.)	[0]
(Unsure/guessing/lost/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Frequency determines the type of wave and not wavelength? I thought different kinds of light have specific wavelengths." (If you always compare different types of light in the same medium (such as vacuum), then it doesn't matter if you compare different types of light in terms of different frequencies or different wavelengths. But for light going from one medium into another medium, the frequency will remain the same, while the wavelength will change. So it will make more sense to describe light in terms of frequency, as that will always stay the same no matter where that light goes, as an x-ray in air will remain an x-ray as it goes underwater (as its frequency stays the same), even though its wavelength will not stay the same.)

"Why does the energy of a wave increase as its frequency increases, and at what point is this energy enough to cause biological harm?" (It takes energy per time to continuously wiggle charges to produce light waves, and the faster you wiggle, then the more energy you put into the wave, so "faster wiggling" (higher frequency, smaller wavelength) light sends out more energy for a given amount of space. For radio waves, this is a low frequency, low energy wave that is "spaced out" a large distance (long wavelength), so it's not so dangerous. For infrared waves, this is a medium frequency, medium energy wave that is "more compact" (medium wavelength), so the cells in your body receive this energy, and (safely) warm up. For x-ray rays and even shorter frequency waves, these high frequency, high energy waves are "scrunched in" (small wavelengths), so dangerous amounts of energy can be absorbed by individual molecules or atoms in your cells and DNA, causing damage.)

"I understood most of Snell's law I think. It was nice having lab before lecture and then homework about it."

"I'm sure you said in lecture but we are calling refracted rays 'transmitted' rays right?" (Yes.)

"I'm slightly confused in the total internal reflection section. So when the incident angle is greater than the critical angle, it internally reflects so there's no transmitted angle?" (That is correct.)

"Could you go more in to detail about the three specific cases and how to use Snell's law with the weird case?" (We'll do that in the form of a flowchart.)

"Could you go into polarization a little bit before you let us loose on the worksheets?" (Yes, both today and next Monday.)

"Can light only exist vertically, diagonally, or horizontally polarized, or is it possible to send polarized light in a spiral?" ("Spirally polarized" light is what is known as circular polarization.)

"So both emitting and receiving antennae need to be with both horizontal or both vertical, would it just not work if there was one horizontal and one vertical?" (Correct!)

"No comment."

Online reading assignment: electromagnetic waves, reflection and refraction

Physics 205B, spring semester 2019
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.


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.

"Visible light (what our eyes can perceive) only takes a small portion of the electromagnetic spectrum and the rest can only be recorded through the use of certain instruments."

"That wave speed and wavelength are affected by change in medium but how frequency is not. Previously I didn't quite understand why but it makes more sense when you say it, because it's from a source (I thought of it like a projector or flashlight being the source)."

"One thing I did understand was the independent and dependent variables for electromagnetic waves. The wavelength is dependent on the speed and frequency of the waves. The speed is independent and set by the medium and the frequency is independent and set by the source."

"Light changes its speed as it passes through different things. The index of refraction helps calculate the speed. Light travels quickest through a vacuum and slower through other materials."

"Indices of refraction describe the speed at which light moves through a medium. In a vacuum n = 1 and the speed of light equals the maximum. In other mediums, light moves slower and n > 1."

"That reflection is light bouncing off a surface where refraction is light bending because it travels through materials with different indices of refraction."

"There are two ways to redirect light, one is to reflect the light which means that the light will bounce off the surface and leave at the same angle in which it first interacted with the surface. The other way is by refracting the light."

"If light travels from smaller refractive index to larger, the refracted ray is bent towards the normal. If on the other hand, light travels from larger refractive index to smaller, the refracted ray is bent away from normal. this relationship is known as Snell's law of refraction."

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.

"How a light wave has the same frequency as it travels from one medium to another medium."

"When it came to refraction, I was having a difficult time comprehending the concept behind Snell's law. The equation shown did not help much with the explanation, but the simple 'fast-to-slow' and 'slow-to-fast' phases helped get the point across bluntly."

"The 'fast-to-slow' and 'slow-to-fast' phrases were a bit confusing. Although it was mostly trying not to mix them with each other."

"Snell's law came off a little bit confusing since the concept makes sense, but applying numbers kind of throws me off, so some examples in class might clarify my concerns. The index of refraction equations make sense, however some examples in class would be helpful in getting a better understanding in solving. Essentially the ideas make sense, but once they are thrown into math-like equations, I can have a hard time translating, so tutorial-like demonstrations can help clarify the transfer."

"Refraction is a little confusing for me, just being able to comprehend what is happening. I know what refraction looks like in different scenarios, but I have a hard time with being able to understand what exactly is happening with the light."

"I experienced difficulty trying to interpret the Snell's law slides. I was hoping the diagrams that accompanied the laws would be beneficial but I don't think I completely understand their relationship or where sine comes into play. I could use so extra time in class explaining this law."

Consider light traveling either through air (n_air = 1.0) or through water (n_water = 1.33). Light travels with the faster speed through:

air.	******************************** [32]
water.	**** [4]
(There is a tie.)	[0]
(Unsure/guessing/lost/help!)	** [2]

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 [71%]
frequency f: remains constant [63%]
wavelength λ: decreases [50%]

For the above example of light incident in air being transmitted into plastic, __________ has the greater index of refraction.

air.	***** [5]
plastic.	**************************** [28]
(There is a tie.)	[0]
(Unsure/guessing/lost/help!)	***** [5]

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 [53%]
frequency f: remains constant [66%]
wavelength λ: increases [58%]

For the above example of light incident in plastic being transmitted into air, __________ has the greater index of refraction.

air.	************************ [24]
plastic.	******* [7]
(There is a tie.)	[0]
(Unsure/guessing/lost/help!)	******* [7]

State your preference for denoting the inverse sine operation.

Arcsin.	* [1]
sin–1.	***************************** [29]
(No preference.)	***** [5]
(Unsure/guessing/lost/help!)	*** [3]

Pick one piece of student advice from the previous semester, and discuss why you agree (or disagree) with it.

"'Stay on top of homework!' After taking Physics 205A last semester I definitely agree with the advice of doing all the work and coming to all the classes. Even if you understand the concepts, there's still more to build upon in class."

"'Always, always do the work. It's easy points and can make the difference when passing the class.' Don't procrastinate because things can really pile up which can be overwhelming. Also don't forget to do the homework because they are a fairly easy way to earn points."

"'Don't give up early on.' Physics is a tough subject and quitting will not get me anywhere. Their advice on doing the homework, going to class and to do the labs are helpful. I was doing the same thing in Physics 205A and it helped. I will try and take their advice and get study buddies to better understand the material and work together to figure out the problems. They stated to learn the website and I have been. It was confusing to first but mainly because I was not used to it. I think I have it down for the most part."

"'Try to ask questions.' My regret from last semester was having a lot of questions but never raising my hand in class when I had concerns. I also think it's important to stay on top of the homework rather than categorizing it as a second thought and waiting until 10:00 PM to do it just hours before it's due."

"'Practice, practice, practice solving all the example problems given to you. Also, it helps a lot to write out short answers on what you did.' Last semester I struggled with short answers, so I think writing them down as I do the practice problems would help a lot by the time the exams come around."

"'Actually do all the assignments because they do help a lot. I noticed that when I did the reading and homework assignments it was a lot easier to follow the next class.' I agree with this student because last semester I didn't do all the homework and I would be so lost. The times when I would try to catch up on it all, it would be too late to turn in assignments."

"'Disregard trying to read the textbook and read the blog posts carefully instead because the book is not user-friendly.' I disagree--I find the textbook helpful. It may not relate to this class as much as the online lectures, but reading the textbook before helps me familiarize myself with what the lecture is referencing. I think I will remember more if I continue to read the textbook as an introduction to topics and use the lecture to dig deeper and solidify my learning."

"'Read everything on the waiferx.com course website because there are no reminders and it is not organized like Canvas.' I agree with this comment. It took me a while to get used to understand the format of this class, so missed out on a lot of points I would have easily earned."

"'I suggest the future students take notes while reading (the night before lecture), to better understand the material. Take notes again in class!' I agree with this piece of advice a lot. Partway through last semester I started taking notes on the material I was reviewing before lecture and it really helped my comprehension during the next class period. The information was fresh in my mind and my notebook plus it helped me have confidence knowing at least a little bit about what we cover in class."

"'The grade you get is how much time you put in.' This is probably the most universal advice I've read on the page. It encompasses all aspects of being an effective student, and has rung true for most of my academic career."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"What are all these angles about?" (All these angles are necessary to measure the directions and changes in directions of light rays--which is what optics is all about.)

"How different is the 11th edition textbook from the 10th or 9th editions? Can a student get by by using an older version?" (The primary difference is the re-numbering of the end-of-chapter problems; you should be able to get by if refer to a classmate's current edition and renumber the problems by hand in your older edition.)

"How exactly do your lectures go? My previous instructor would just go over presentation slides, and the class felt repetitive." (Class is pretty fluid in terms of allocating time between presentation slides, lectures, examples, worksheets, and problem-solving; it all depends on what level of understanding/comprehension the class has and what level of introduction/challenges the class needs. Typically Physics 205A last semester had some review of a presentations slides and introductory lectures, with mostly a mix of examples, worksheets, and problem-solving.)

"I will say at first I was skeptical of the flipped classroom structure, but I have to say I very much enjoyed last semester and it is one of my favorite learning styles, because I learn best by doing it myself at home, such as going over the notes and doing the problems. This in turn has helped me in other classes."

"How was your winter break?" (It was quite relaxing. Hope you enjoyed yours as well.)

"I hope this is another great semester!" (I hope so, too!)

"I'm sorry P-dog but believe it or not, the beginning of this particular semester is actually difficult. But I can reassure you that I am still a hardworking student!"

Physics midterm question: wavelengths at total internal reflection interface

Physics 205B Midterm 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Light of wavelength 533 nm in a unknown material (index of refraction n₁) undergoes total internal reflection from an interface with a different unknown material (index of refraction n₂). (Drawing is not to scale.) Show that the wavelength in the n₂ material would be longer than 533 nm (assuming that light could eventually be transmitted out in the n₂ material). Explain your reasoning using the properties of light and refraction.

Solution and grading rubric:

• p:
  Discusses/demonstrates that the wavelength λ₂ in the second n₂ material would be longer than 533 nm by:
  1. qualitatively or quantitatively showing that n₂ < n₁ by appealing to the critical angle θ₂ = sin⁻¹(n₂/n₁) (where n₂ < n₁ in order to avoid a domain error in the inverse sine function); or Snell's law n₁⋅sinθ₁ = n₂⋅sinθ₂ where θ₂ = 90°, and thus n₂ < n₁; and
  2. that since index of refraction n = c/v, a smaller index of refraction n₂ results in a faster speed of light v₂; and
  3. since the wavelength λ = v/f, since the second material has a faster speed of light v₂, and the frequency of light is independent of the medium it travels through, then it will have a longer wavelength in that material.
  May combine arguments in (1)-(2) by arguing that total internal reflection occurs when light traveling in a slower material is "frustrated" in trying to travel out into a faster material.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically one of arguments (1)-(3) missing, incomplete, or problematic.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. Typically two of arguments (1)-(3) missing, incomplete, or problematic.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying Snell's law and/or critical angles, indices of refraction, wave speed, frequency and wavelengths.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying Snell's law and/or critical angles, indices of refraction, wave speed, frequency and wavelengths.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01cVdP
p: 17 students
r: 6 students
t: 9 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 3673):
A sample "p" response (from student 1929):

Physics quiz question: water wavelength in spharelite

Physics 205B Quiz 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Light of wavelength 476 nm in water (index of refraction[*] of 1.33) with an incident angle of 16.0° 
is transmitted into sphalerite (index of refraction of 2.43). (Drawing is not to scale.) The wavelength of this light traveling through sphalerite is:
(A) 196 nm.
(B) 261 nm.
(C) 358 nm.
(D) 870 nm.

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (B)

The relations between the index of refraction and the speed of light, for water (medium 1) and for spharelite (medium 2) are:

n₁ = c/v₁,

n₂ = c/v₂,

where the given (or assumed to be known) quantities, unknown quantities, and quantities to be explicitly solved for are denoted. Also the relations between wavelength, speed, and frequency are:

λ₁ = v₁/f₁,

λ₂ = v₂/f₂.

However, the frequency of the light in spharelite is the same as the frequency it has in water, such that:

f₁ = f₂,

(v₁/λ₁) = (v₂/λ₂),

λ₂ = λ₁·(v₂/v₁),

λ₂ = λ₁·((c/n₂)/(c/n₁)),

λ₂ = λ₁·(n₁/n₂) = (476 nm)·(1.33/2.43) = 261 nm.

(Response (A) is (476 nm)/(1.33); response (C) is (218 nm)/(2.43); response (D) is (476 nm)⋅(2.43/1.33).)

Sections 30882, 30883
Exam code: quiz01AM0l
(A) : 4 students
(B) : 28 students
(C) : 1 student
(D) : 2 students

Success level: 80%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64