How Classical Kinetic Energy Is Actually A Subset Of Relativistic Kinetic Energy

Many people think that Classical Physics and Relativistic Physics are two different things. Of course, anyone who has studied both can tell you that one can derive many of the classical physics equations from relativistic equations, proving that classical equations are actually special cases of the more general relativistic equations.

In this Don Lincoln's video, he shows how classical kinetic energy that many students learn in General Physics courses can actually be derived from the more general relativistic energy equation, and why we still use the classical physics equation in most cases.

Z.

Electrons Behave Like A Fluid - Exhibit Vortices

This is a rather cool experiment.

They have a direct observation, for the first time, of electrons behaving like an ordinary fluid and exhibiting vortices  when going thorough a channel.[1]

In contrast, electrons flowing through tungsten ditelluride flowed through the channel and swirled into each side chamber, much as water would do when emptying into a bowl.

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“That is a very striking thing, and it is the same physics as that in ordinary fluids, but happening with electrons on the nanoscale. That’s a clear signature of electrons being in a fluid-like regime.”

So far, "ordinary" electron flow behaves like a "Fermi liquid", which is not like ordinary fluid flow. To get electrons to behave this way, they had to make sure that the electrons do not bump into the crystal lattice (the bulk material), so this is not easy since normal-state electrons usually have such interaction (non-zero resistivity).

Just to be clear, this is not the first observation of electrons exhibiting vortex flow. This is a common observation when they are in a superconducting state, where vortices form around magnetic flux lines that penetrates Type II superconductors. But in that case, these electrons are in a superfluid, and what is flowing is the paired electrons (Cooper pairs).

In this experiment, these are individual electrons not in a superconducting state, so this truly is a river of electrons.

Z.

[1] A Aharon-Steinberg et al., Nature 607, 74 (2022).

My Favorite Web Applications - Part 6

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

My favorite web applications - Part 3

My favorite web applications - Part 4

My favorite web applications - Part 5

Continuing on with my pet project here, this next web application is actually another one of those that closely mimics an actual experiment. This time, it is on specific heat, and the goal here is to measure the specific heat of an unknown liquid. You do this by measuring the mass and temperature of the unknown liquid, and then mixing it with hot water of known mass and temperate. By finding the final equilibrium temperature, you then calculate the specific heat of the unknown liquid.

Like I said, this web experiment is done step by step just like a real experiment. In fact, you could use this as the lab instruction and get the students to follow each step of the experiment. But what I like the most is that each student will be given a different set of numbers to work with. The masses will be different, and so will the starting temperatures of the liquid, resulting in different final temperature as well. I don't remember if the specific heat of the unknown liquid is also different for different students. Please let me know if you've used this app or if you discover this later on.

I used this as one of my virtual labs when we went remote. But I continue to use this after we gone back to face-to-face classes as part of my in-class problem solving exercises. I've also given this as a take-home homework problem, and they have to show the final acknowledgement page that they got this correct if they want to receive credit for it. If the students have done the actual experiment itself, this web application will be quite familiar and they should have a good clue on how to correctly find the unknown specific heat.

Zz.

Share It, Don't Split It - Is It Working?

I'm teaching a physics course with labs over the summer. And if you've taught Summer courses, you know that they go very fast and furious, so I'm not sure if there's any chance for any evaluation on the effectiveness of anything.

I mentioned a study a while back that seems to imply that it is better for students, especially minorities and marginalized students, to share lab work and have equal access to every part of the experiment, rather than splitting responsibilities and have each students just do one part of it. I am still unsure of how effective it is or whether I can tell if it is working, but I've made sure that the students know that no one is to do just one part of the experiment, that everyone must take turns doing different parts of the experiment.

Much to my surprise, the students seem to be amicable about it. So far, I've seen everyone taking turns and rotating themselves to different tasks as they perform the experiment. Better yet, I've seen students helping and teaching other students on what they just learned about doing certain parts of the experiment or in performing the analysis of the data.

One direct result that I've seen so far is that everyone in the group knows how to work and setup the computer interface to connect to the various sensors, whereas in previous classes, I've noticed that the same students had the responsibility of setting up the sensors. Already, I can tell that the students are learning about conducting the whole experiment rather than only certain parts of it.

I did not plan on doing any form of assessment on how beneficial or effective this is, because I had not run any control study before. Besides, it is a summer session, and "rushing" is the most common theme for a physics summer class.

I don't know if this will boost the students' "self-efficacy" but from simply a superficial observation, I can see the benefit of requiring that the lab work be shared rather than split.

Zz.

My Favorite Web Applications - Part 5

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

My favorite web applications - Part 3

My favorite web applications - Part 4

This time, it is an experiment that mimics the fabled Archimedes experiment where he supposedly determined for the "king" whether the crown was made of pure gold or not. This web application basically allows a student to perform a similar virtual experiment to determine the density of the object being investigated.

There are two reasons why I like this app. The first reason is that if you change the default settings for the mass and the volume, you will given rather random values. This means that each student will have different values for the mass and volume, resulting in each student having a unique set of data and calculation.

The second reason why I like this "experiment" is that it actually is the same experiment that we would do in a f2f lab. We use PASCO's Capstone system, and one of the experiments that we do is practically identical to what is shown in this virtual experiment, where a student has connected a weight sensor to a hanging mass, and then he/she slowly lowers it into a beaker of liquid. The sensor sends a reading of the hanging weight value to a data collection system that plots the value of the weight in real time. As the weight is lowered into the liquid, the data being plotted looks almost exactly as what is shown in the virtual experiment in this app. The weight changes due to the buoyant force of the liquid.

The analysis of the experiment and the extraction of the value of the object's density are similar for both the f2f lab and this virtual lab. So in that sense, the student is not being deprived of much of the physics. There are, of course, more errors involved in the real experiment because often the object isn't hanging still, and the movement adds more noise to the data. The app doesn't allow the data to be extracted directly, so no curve fitting or calculation of average value can be made for a range of the data points, something the students in the f2f lab are asked to do to be able to determined the weight before and after immersion.

Still, it is an adequate virtual experiment, especially since each student will have to do his/her own analysis on a unique set of measurement. I actually have used this as part of an assessment where this app was part of an exam for a f2f class (before the pandemic). The student had already done the actual experiment, so they should be familiar with how to find the density of the object using this app since things should look rather familiar.

Zz.

 

The Migration to OER

For the past couple of years, the school has been pushing various departments to start adopting Open Educational Resources (OER) for various courses to help reduce educational costs to students. It has finally trickled down to our department where, starting this coming Fall, the General Physics courses will start using OER texts for the first time.

I have zero problem with doing this. I remember when I was a student, textbooks were hugely expensive. Adopting OER texts for General Physics courses will save students quite a chunk of change, especially if they, or their parents, are footing the costs.

The only issue I have is that, using texts from various publishers doesn't stop just at the textbook itself. I've been using Pearson and Cengage for General Physics texts, and they come with their online services consisting of the e-text and homework/quizzes capabilities.

But even that does not convey everything. Both Cengage and Pearson's website offers rather substantial student support that I have made used of, especially when we went remote. When I assign homework on Pearson's Mastering website, for example, I often select one or two "tutorial" items. These are questions in which, if the students are stuck, there are guided hints and prompts to help students overcome the barrier or difficulty at that stage. I find these types of tutorial very useful for the students and often had the students attempt one of them during class session.

The other thing that I find useful is the "adaptive learning" feature. I can set it up so that if a student struggled with one problem and finally thinks that he/she understood how to solve it, it will prompt the student to solve a similar problem to that one to see if the understanding can be nailed down. The student then has the chance to really test his/her understanding in solving the similar problem, and I can see for certain of the student's progress.

Unfortunately, none of these extensive feature are available in any of the OER sources. These features were extremely useful during remote learning where I'm not there to help the students in person. Yet, these features gave real-time feedback on how the students are doing and assisting the students in solving the problem, all done automatically without needing my intervention. These are what I will miss when I start using OER texts because so far, from what I can see, they only provide the text and maybe a set of homework questions, and that's it. It is no different than the old-fashioned way when I was in college, except that these are in electronic form.

It is still months away from the start of the Fall semester, but I'm already thinking and planning ahead on how to approach this. We will definitely be back to in-person instructions, so maybe the need for all the bells and whistles of online capabilities might not be as great as it is now. Still, I'm anticipating a few hiccups as I dive into a new set of challenges in running a class.

Stay tuned....

Zz.

Signature of Tc Inside the ARPES Pseudogap?

The physics of high-Tc superconductors (or the cuprate superconductors) continues to be elusive. After its first discovery in mid 1980's, a coherent and consistent theory on why this family of material becomes superconducting is still up for debate. There are candidate theories, but we do not have an accepted consensus as of yet.

One of the main reason for this is that this is such a rich and complex material, exhibiting so many different characteristics and puzzles. As a result, different versions of theories are competing to describe as many of the experimental results as possible. But the target is also moving. As our instrumentation improves, we are discovering new, more subtle, and more refined behavior of these material that we haven't seen before.

The existence of the so-called pseudogap in the cuprates is well-known. I've posted several articles on them. This is the gap in the single-particle spectral function that opens up well above the transition temperature Tc. In conventional superconductors, the formation of this gap coincides with Tc, below which the material becomes superconducting. However, in the cuprates, and especially in the underdoped cuprates (less oxygen doping than the optimally-doped), a gap opens up well above the Tc. The material doesn't become superconducting yet even as you lower the temperature even more. It is only when the temperature gets to Tc will the material becomes superconducting.

The origin of this pseudogap has long been debated. The posts that I had made discussed all this. However, in this new paper published in Nature (the article I linked too erroneously wrote "Science" at the time of this citation), the Z-X Shen group out of Stanford has detected the signature of Tc in the pseudogap region from ARPES measurement. But what is interesting here is that it was detected in the overdoped cuprate Bi2212.

Typically, the overdoped regime of the cuprates does not exhibit clear pseudogap signatures. When I studied a highly-overdopped Bi2212 using ARPES a long time ago, we did not detect any pseudogap at all since we saw the opening of the gap only at the bulk Tc value. Of course, this does not mean it wasn't there because it depends on the temperature resolution of our experiment. So it is rather interesting that this study decided to focus on the overdoped region where the pseudogap is more difficult to detect, as opposed to the optimally-doped or underdoped region where the pseudogap is much more obvious.

In any case, they apparently saw spectroscopic signatures of Tc within the pseudogap as the material cools down through Tc. According to them, this seems to be a strong evidence in support of a phase fluctuation (spin fluctuation?) model as the driving mechanism for superconductivity in these materials.

I tell ya, almost 40 years since its discovery, the cuprates continue to amaze and surprise us!

Zz.

The Future of CMB Exploration

You would think that once the cosmic microwave background (CMB) has been discovered and studied, that was the end of it. That is not how science typically works, especially on something that has such a rich amount of information as the CMB.

This article reports on the next proposed major research effort in the US in further studying the CMB and refining the measurements that we currently have. The article gives you a good over view of what we currently know about the CMB, what we wish to extract out of it, and how it can be done. This appears to be a joint effort between two major science funding agencies in the US: the US Dept. of Energy and the US National Science Foundation, and will have an estimated cost of $650 million.

As someone who likes to include contemporary and most recent relevant news into my lessons, this will be another item that I will include in my Intro to Astronomy class.

Z.

My Favorite Web Applications - Part 4

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

My favorite web applications - Part 3

Of course, I have to include a PhET application. How could I not? It is such an amazing collection of very useful applications and simulations.

For this one it is the demonstration on Faraday's/Lenz's law. What is interesting about this is that, if you have read one of my previous posts, I use this not so much as a virtual lab, but rather as an in-class "discovery" tool. In fact, for my f2f classes, I had an identical setup to this PhET application sitting in front of the students at the beginning of class. So the instruction that you'll see given to the students is almost identical for this application and for in-class activity.

This obviously is a lesson on Lenz's law. Instead of starting the lesson with a lecture, I give the students a series of tasks for them to do. I first tell them to set up the application or in-class apparatus to look like the picture below:

We then spend some time discussing the direction of the current in the coil if the galvanometer (in-person) or the voltmeter (PhET) has a positive or negative deflection based on being observed from the right side of the coil.

Once the students have established this, I give them a series of tasks that they have to perform and to record what they observe. The tasks are listed in the table below:

When we were doing this in-person, I asked the students to perform Task 1, to record what they observed, and then we all, as a class, discuss the observation. This exercise was helpful especially to students who were still unsure on what to do and what they should be observing. So this first tasks often clarified further what they needed to perform and what they should observe. For remote classes, this is not that easy mainly because I don't quite see what they students are doing and what they are observing. They are also doing this in their separate Zoom breakout rooms. They have a chance to discuss with members of their group, but I am not always there to double-check what they are observing. I do, however, get to see what they are recording because the table above is posted on a Google Slide document that I give them. So I can see every entry for each group and able to step in if I see something not quite right.

In any case, the students for in-person session perform the task one step at a time, and each time, we all discuss the observation. Remember that I have not told them anything about Lenz's law at all. All they are doing at this stage is performing a task and recording the corresponding observation.

By the end of this activity, both the in-person and remote students will have a set of observations for each of the tasks performed. This is where it gets interesting. I then instruct the students to discuss with their group members on how to come up with a set of rules or "laws" to accurately describe the behavior of the current in the coil in relation to what the bar magnet is doing. In other words, I want the to come up with a written description of Lenz's law.

Of course, I give them hints. The biggest hint is for them to consider the induced magnetic field in the coil. By that point, they have learned that a current in a coil or solenoid generates a magnetic field. If there is a deflection in the galvanometer/voltmeter, then there must be a current in the coil. The positive or negative deflection indicates the direction of the current in the coil, which in turn indicates the direction of the induced magnetic field in the coil.

From my experience in doing this for several semesters, only about 1/4 of the students were able to come up with a description that had a close resemblance to Lenz's law. Many of them struggled not just in understanding what they observed and what the "laws" were, but also in communicating accurately and clearly what they intended to say. The latter is a very common problem for many students trying to write scientific prose.

However, regardless of whether they managed to successfully come up with their own version of Lenz's law, I find that this exercise demonstrates this principle a lot clearer than if I just simply spew out the material in a lecture. Even if the students could not communicate clearly what they understood, most of them actually had some realization of what it is. To me, this is the biggest stumbling block in understanding Lenz's law, which was the impetus for me to present this topic in this manner.

The PhET application allowed me to do almost the same activity online as the one I do in-person. That is a very good thing!

Zz.

My Favorite Web Applications - Part 3

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

Continuing with this series, here is my next favorite web application. This is a virtual experiment on measuring the specific heat of an object. The fun thing about this particular application is that (i) it is very similar to what we normally do in a real experiment and (ii) one can also use the step-by-step instruction as part of the experimental procedure, thus the name "Guided Specific Heat.... ".

Similar to the force table experiment that I cited in Part 2, this one also has randomized values for each person going through it. It randomizes the mass of the cold water, the mass of the object, and uses different specific heats. Each student doing this online will have a different answer.

When I assigned this to the students during our remote sessions, the students had to fill in all the information obtained during each step, i.e. measurement of the mass, etc. Then, during the actual measurement, once it stopped, the students had to do a screen capture of the graph of Temp. vs. time to paste in their report. They then had to show their work on how they arrived at the specific heat value of the object. If they entered the correct answer, the application acknowledges that and they should also do a screen capture of that to paste in the report. If they got it wrong, then they had the option of either submitting what they had and take the deduction for the wrong work and answer, or redo the experiment from the very beginning. They get to do this as many times as they wish until they get it right.

I also added an extra part where I asked them to think of the kind of errors and uncertainty in the experiment, especially if this were done in real life.

To double-check the students' answers, I created a spreadsheet where all I needed to do was to enter the mass of the object, mass of the cold water, and the final temperature. 

I like that each student will have a different answer. It added an extra layer where they could not just copy off each other's work directly. The experimental procedure is also almost identical to one of our experiments on specific heats anyway, so I didn't have to make huge modification to the instruction.

Now that we have gone back to f2f classes, I'm using this exercise as part of a homework assignment.

Zz.

Are Physics Papers Authored By Women Cited Less Than Those By Men?

So I'm reading this article in Physics Today of a study done on citation numbers and frequency of citation of papers where the first and/or last author is a woman. They found that papers authored by women tend to get less number of citations than men.

The number of papers authored by women in the eight physics subfields examined in the study almost doubled between 1995 and 2020, from around 17% to roughly 33%, as shown in the graph above. But those manuscripts attracted about 3% fewer citations than expected, whereas those whose first and last authors were men were cited roughly 1% more.

What’s more, the gender gap was largest in papers authored by men. According to the study, manuscripts with male authors cited recent male-authored papers about 2% more than expected and cited recent papers authored by women 6% less. Studies with a female author over-cited recent female-authored papers by 3% and under-cited recent papers by men by 1%.

Hum... But then they also say this:

One limitation of the study is that it couldn’t decipher the gender of about one-fifth of the authors, those who list only their initials instead of their first names, Bassett notes. Although Bassett says she and her team excluded those authors from their sample, McCullough thinks a significant number of them could be women. She says women in science often hide their first names to avoid discrimination.

Another problem, Bassett says, is that the software determines the chance of an author being a certain gender on the basis of his or her name, but it will be wrong at least some of the time, especially for gender-neutral names. It also cannot identify nonbinary individuals.

As someone who has read, and continues to read a lot of physics papers, the LAST thing I pay even any attention to is the gender of the authors. In fact, it is a common practice (and certainly in the groups that I have worked with) that when we publish a paper, we tend to only include first-name initials in the authors list rather than full name. It is also from my personal experiences that many of the papers that I have cited turned out to have women as first authors. No one could tell just by looking at the authors list that "K. A. Moler", "N. Trivedi", and "K. Levin" are women, for example.

Coupled with the fact that they found 3% fewer citation for women and that their study had to exclude about 20% of the authors because they couldn't tell their genders, this observation is not very convincing to me.

Zz.