Thursday, April 18, 2024

Double Slit Ahead of Single Slit?

This is similar to my earlier query regarding the sequence of topics that are introduced. My earlier post was the order of introducing the concept of energy and the concept of momentum. In this post, it is the issue of the sequence of introducing the double slit interference ahead of the single-slit diffraction.

This sequence is done in Knight's text "Physics for Scientists and Engineers". I don't follow that sequence because I prefer to introduce the single-slit diffraction first, show the diffraction pattern, and then introduce the double slit. The fact that the double slit pattern has interference pattern inside a single-slit diffraction envelope is easier to explain after the students already know about the single-slit diffraction.

What do you think? How did you teach this topic, or how did you learn this topic?


Saturday, April 06, 2024

Livestream of Total Solar Eclipse 2024

The US National Science Foundation (NSF) will be livestreaming the total Solar Eclipse of 2024. Here is the blurb from them:

Don't just watch the eclipse — explore it. On April 8, the U.S. National Science Foundation and the NSF National Solar Observatory are hosting an educational livestream all about the science of the sun.  

The livestream is a free resource that educators can use in their classrooms to share the excitement of science.  

You'll hear from scientists about the unique experiments happening during the eclipse. As we count down to the moment of totality, you'll learn about:  

  • The different layers of the sun, from the core to the corona. 
  • The world's largest, most advanced solar telescope.  
  • How massive solar eruptions generate space weather. 

It all happens on YouTube on April 8 starting around 11 a.m. PDT/noon MDT/1 p.m. CDT/2 p.m. EDT.

Friday, April 05, 2024

Doppler Ultrasound Uses Confusing Color Scheme

In my algebra-based General Physics courses, I get many Biology/Pre-med/Life Science majors, so of course many of the examples that I choose tend to be related to those areas. When we cover traveling waves and Doppler effect, I dive into medical diagnostics to show a few of the applications of Doppler effect in that area.

Interestingly enough, in Doppler Ultrasound, the color scheme that they use tend to be a bit confusing with what we use in physics. In the Doppler effect, when the source of a wave, or the source that is reflecting the wave, is moving away from the observer, the wavelength will be longer than the original wave. We popularly say that the wave has been "redshifted". This is because in the visible spectrum, the longest wavelength is toward the red color.

Conversely, if the object is moving toward the observer, then the wavelength will be shortened, and thus, "blueshifted", since blue (or violet) is the shortest wavelength in the visible spectrum.

But this is not the color scheme adopted in the field of Doppler Ultrasound, as represented in this video:

It seems that if the flow is toward the transducer, it is given the red color while if the flow is going away from the transducer, it is given a blue color.

Obviously, this is not a source of confusion for people in that field since they don't normally encounter those color-shifted lexicon, but for students who are studying this topic for the very first time, this takes a bit of an effort to make sure they do not become confused with the contradicting color scheme. The first time I used the Doppler ultrasound example was, unfortunately, right after I discussed an example from astronomy where I indicated that most of the light from the galaxies are redshifted and thus, a strong evidence that the universe is expanding since those galaxies are moving away from us. You can imagine that the students who were paying attention got a bit confused because the blood flowing away from the transducer is now being labeled with blue color instead of red.

Does anyone know why this field adopts this color scheme? 


Monday, April 01, 2024

AI Will Pick Nobel Prize Winners in Physics

Please read the article carefully before you freak out. Hint: look at the date.


What's In A Physics Word?

This is a rather fun article in this week's Nature. It reveals some of the fascinating origin of words used in Physics and how they may not match the more common usage of the word.

All of us in physics (and in science) know of this, where we may use the same words that are used in everyday language, but they have very different meanings in physics. Unfortunately, for many people outside of physics, this can lead to a lot of confusion or misuse if they do not investigate or understand the meanings of those words as used in the context of physics. The word "spin" comes to mind when talking about the quantum spin of elementary particles.


Friday, March 29, 2024

My Favorite Web Application - Part 8

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

My favorite web application - Part 6

My favorite web application - Part 7

This is another one of my favorite web application because it has a ability to assign random values to various parameters in the problem.

This is a simulation of a motional emf in the form of a rail gun. It actually is a straight-forward application of magnetic force acting on a straight current. One may also solve this using Faraday's law, but it is not as straight-forward to solve because the magnetic flux (or rather, the area) does not change uniformly since the rod is accelerating.

What I also like about this simulation is that one can also tie in with what the students learned in Physics 1, i.e. they may verify their answer using kinematics, since we know the rod's mass, and it starts moving from rest. Knowing how far it travels and a good estimate of the time of travel gives us the value of the acceleration, and thus, the force acting on the rod. This should match with the magnetic force.