Mastodawn

Reading the dissertation was fascinating because it reveals a side of #Helmholtz that is rarely discussed today. Long before his work on #EnergyConservation, #electrodynamics, and #WavePhysics, he was already deeply engaged with #anatomical and #biological questions.

It also shows that some core ideas about the comparative structure of nervous systems were already being articulated in the early 19th century.

#Neuroscience #Physics #ScienceHistory

Rhett Allain May 3

I got a little long, but here is my full derivation of why a hydrogen atom is not like a tiny solar system. #physics #electrodynamics

https://rjallain.medium.com/atoms-arent-tiny-little-solar-systems-electrodynamics-shows-why-it-would-collapse-90c5255d58c5?sk=9b5e6b9d129221c0b8c24d182e0f530a

Atoms Aren’t Tiny Little Solar Systems. Electrodynamics Shows Why It Would Collapse.

One of the early models for the atom had a positive nucleus with electrons orbiting just like a tiny solar system. But there’s a problem…

Medium

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Rhett Allain Mar 31

Here's a #python animation I made for #electrodynamics

Rhett Allain Mar 31

New #electrodynamics #physics video - looking at reflection and transmission of electromagnetic waves. Snell's law and Brewster's angle.

https://youtu.be/_dFKj6OE05I

Electrodynamics: Reflection, Transmission, Snell's Law and Brewster's Angle

YouTube

j_bertolotti Mar 16

#PhysicsFactlet
Scattering VS Extinction
In #Optics, the concepts of scattering and extinction are closely related. So closely related that many people tend to confuse them.
Imagine to illuminate a small object with a beam of light. If the object is small the scattered field will be essentially a spherical wave, and the total field will be the incident one plus the scattered field.
If we were able to measure directly the field (as we can do in the microwave regime) we could happily stop here, but in optics we can only measure intensities, and the intensity is defined as the time average of the modulus of the Pointing vector. In most cases of interest, the modulus of the Poynting vector is proportional to the modulus squared of the electric field (which explains why we often that a shortcut and just talk about |E|²).
So the quantity we measure is proportional to |Eᵢₙ +Eₛ|², which is the sum of the Poynting vector of the incident field, the Poynting vector of the scattered field, plus the cross terms. These cross terms are what we usually call "extinction" and are the result of the interference between the incident and scattering fields(and the reason why you get a "shadow" behind the scatterer).

#Scattering #Electrodynamics

Rhett Allain Mar 13

Here is my lecture on EM plane waves for #electrodynamics #physics. Yes, I include a #python model for a plane wave

https://youtu.be/260PsZEiFuE

Electrodynamics: Maxwell's Equations and Plane Waves

YouTube

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Rhett Allain Mar 13

Here is circularly polarized wave - from #electrodynamics #physics using #python

Paul Balduf Mar 7

#paperOfTheDay "On the identification of gravitation with a massless spin 2 field" from 1986. This article deals with the general theory of #relativity . Namely, if one starts from a generic field theory of a spin-2 particle, the resulting theory has a symmetry that suggests to identify it with general relativity. However, if one stays as closely as possible analogous to #electrodynamics and the conventional assumptions of field theory (fields decay at infinity), then the only possibility seems to be that the universe is asymptotically flat an has no holes or any other topological features, and the cosmological constant must be zero.
I am not sufficiently familiar with general relativity to assess if this is in fact the only possible conclusion. In any case, the paper is a nice exposition of field theory with spin 2, a topic which is not usually covered in introductory physics lectures.
https://link.springer.com/article/10.1007/BF03053785

On the identification of gravitation with a massless spin 2 field - Acta Physica Hungarica

The identification of gravitation with a massless spin 2 field (the gauge group is the symmetry group of translations) requires to restrict the solutions of Einstein’s equations to the class of topologically trivial manifold. It is shown that the validity of this restriction in nature is supported by the present-day empirical facts. The identification has a drastic impact on cosmology, because the fulfilment of the cosmological principle is claimed to be improbable.

SpringerLink

Michael Katzmann🐈Feb 26

This is an interesting paper examining the transmission of DC current as ω→0 in the telegrapher's equation using the Heaviside step function.

Abstract—We explore the question of how direct current (DC) power is transmitted by electromagnetic fields in TEM/Quasi-TEM structures despite the static curl laws ∇ × E = 0 and ∇ × H = J. In this work we treat DC as the long-time limit of a causal step excitation.

https://www.techrxiv.org/users/998334/articles/1358840/master/file/data/Yes__DC_Power_is_Transmitted_by_Electromagnetic_Waves_Preprint_/Yes__DC_Power_is_Transmitted_by_Electromagnetic_Waves_Preprint_.pdf?inline=true

#maxwell #electrodynamics #radio

Rhett Allain Feb 11

I think this #physics #python video turned out better than I expected. Verifying Faraday's Law for #electrodynamics

https://youtu.be/s666ts_DOkg