Questions tagged [electromagnetism]

Electromagnetism is a branch of Physics involving the study of the electromagnetic force, a physical interaction that occurs between electrically charged particles. This force plays a major role in determining the internal properties of most objects encountered in daily life. Originally, electricity and magnetism were considered to be two separate forces. This view changed with the publication of James Clerk Maxwell's treatise on electricity and magnetism.

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68 views

Did Hertz discover the concept of frequency and if so, how did Doppler think of frequency?

I may not be understanding what a "Hertz" is but it seems to simply be one cycle per second. But would not Doppler have understood what frequency was decades before Hertz? Or was Hertz just ...
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Had Albert Einstein tried to use the Galilean transformation on Maxwell's equations before AE's Special Theory?

I am looking for what motivated Albert Einstein in the direction of his Special Theory. I have read that it is unclear if he was set on that path by the Michelson-Morley experiments. Was AE aware ...
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Who discovered the electric potential?

Wikipedia says that the magnetic vector potential was discovered by Neumann in 1845, by Weber in 1846 and Lord Kelvin in 1847. It does not mention who discovered the electric scalar potential. Hence ...
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Whatever happened to parageometrical optics of diffraction?

In 1950, Giuliano Toraldo di Francia published a paper [1] with the title "Parageometrical Optics" followed by several other papers on the subject, I dare say culminating in a beautiful ...
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Why is the magnetic force on a current-carrying wire sometimes called the Laplace force?

Living in the UK, I've been used to calling the force on a current-carrying wire in a magnetic field 'the motor effect force'. But I'm increasingly aware of another (less clumsy?) name for it: 'the ...
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Who discovered Bremsstrahlung?

I found a web page that says that it was discovered by Tesla in 1890, is that true or generally acknowledged? Isn't 1890 too early a date?
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Demystifying Nikola Tesla: Scientifically sound, historically accurate biography

As any physicist knows, a lot of amateur science afficionados out there bring up Nikola Tesla in rather fantastical ways. There are indeed a few reasons for his near mythical status in popular culture,...
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How was it determined that charge and current were made of the same stuff?

Even in my earliest physics course we took for granted that charges are made of electrons (or their absence) and currents are due to the motion of electrons. But the electron is a very modern concept ...
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de Broglie's conception of the electron

I've been working on de Broglie's thesis (English PDF, Original French PDF) for a course, and I've found something that's been bothering me. My training is in Physics, and so I'm not particularly ...
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Why is wave guide theory developed so long after Maxwell's work was published?

When some fundamental new theory is published, derived work will be done "instantly", example from quantum mechanics: 1926 Schrödinger equation 1927 The first application of quantum ...
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Which scientist(s) first measured the elementary charge and how did they do it? [duplicate]

I would be grateful if anyone could shed some light on these questions. Which scientist(s) first measured the elementary charge? If it wasn't measured in a straightforward experimental setting, and ...
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How did Stern or Gerlach, of Stern-Gerlach experiment, create individual silver atoms? How were they accelerated?

How, a century ago, could Stern and/or Gerlach KNOW that they had created single silver atoms? How were they moved, or accelerated?
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Bohr-Kramers-Slater (BKS) theory and energy conservation only on statistically basis

I was reading Wikipedia article on Bohr-Kramers-Slater (BKS) theory, https://en.wikipedia.org/wiki/BKS_theory. I encountered two interesting points and need your help to understand the reasons behind ...
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How did Lorentz transformations get their modern definition?

Historically, Special Relativity was motivated by apparent inconsistencies between Maxwell's Electrodynamics and Newtonian Mechanics. In Einstein's well known paper "On the electrodynamics of moving ...
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How did Gauss, Ampere and Biot-Savart derive their laws?

Gauss' law for electricity and magnetism, Ampere's law and Biot-Savart's law — all of these laws are crucial for understanding electromagnetism and Maxwell's equations. But I want to know how each of ...
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High voltage / current sources in 19th century cathode ray experiments

In modern chemistry textbooks, a DC source (battery symbol) is usually shown for cathode ray tube experiments by Thomson and others. Certainly, no battery can provide very high voltages needed for gas ...
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Why is the constant of magnetic fields called permeability and that of electric fields called permittivity? [closed]

Basically the title, I found it weird that we use two different names for each fields. What were the reasons for doing so, historically speaking?
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When was the earliest speculation that gravity and electromagnetism had a unified description?

In 1786, Coulomb announced his law that showed that the electromagnetic force between two charged sources followed an inverse square law. Given that gravity followed a similar law, did anyone suggest ...
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When was "Faraday's Law of Induction" first expressed in a quantified form?

An often used definition of "Faraday's Law of Induction" goes something like this (found in Wikipedia) The electromotive force around a closed path is equal to the negative of the time rate ...
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Names of the electromagnetic units in SI

The unit of charge is the Coulomb, named after Charles Augustin de Coulomb. This makes sense because Coulomb's law talks about the force between two charges. But I have seen that the SI unit of ...
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Validity of Maxwell's equations in the aether's reference frame

If Maxwell's equations were experimentally found on Earth such as Faradays law, coulombs law , and worked in the Earth's frame of reference, then why did people believe them to be valid in the aether'...
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Who invented the quadrupole lens for charged particles?

I am wondering who actually invented the (magnetic) quadrupole lens or who used it for the first time. I have found some papers from the 50s and 60s about more complicated systems based on Quadrupoles,...
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Who discovered or predicted an electron g factor of circa 2?

I'm writing a physics article with significant historical content, and I'm struggling to find something. Forgetting about the anomalous magnetic dipole moment for a minute, the electron's g factor is ...
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Historical origin of magnetic monopoles

There are two related historical questions that I'm trying to find answers to: Who was the first to introduce the concept of magnetic monopoles? Griffiths in his textbook Introduction to ...
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How and for what purpose did Lorentz come out with his "electron model"?

Who suggested to him the idea that charge wasn't really some excess or defect of "electric fluid", but rather something carried by a particle?
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How did scientists plot complicated graphs in the 19th century?

I am wondering how did Maxwell in the 19th century draw such figures as the one shown? What tools or procedures did he need? Is it all compass and ruler drawing?
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Which came first, Coulomb's law or Gauss's law?

which one has been discovered earlier? Coulomb's law or Gauss's law? I've read that Gauss's law is more fundamental and of course we can derive Gauss's law using Coulomb's law and vice versa. But my ...
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Who discovered the magnetic vector potential, $\vec{A}$?

Neither Maxwell’s fundamental differential equations on electromagnetism nor Einstein’s first papers considered the magnetic vector potential A. So who discovered, formulated or used A for the first ...
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Did the principles of celestial mechanics affect the development of electromagnetism?

Much of the early theoretical work in electricity and magnetism appears to have been the result of applying celestial mechanical principles to electrostatics. Examples include Cavendish's inverse-...
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What is a Heaviside rational current element?

This terminology seems to be referred to a notion invented in an old book of Oliver Heaviside [1]. What is it and why the Biot-Savart law is not unique unless it is applied to a Heaviside rational ...
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How was charge to mass ratio measured via electrolysis in 19th century?

I think this question is useful to know how sir J.J.Thomson inferred from his experiment that the electron had to be 1700 lighter than hydrogen, as he declared in his Nobel Lecture of 1906: Before ...
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How did physicists deal with the variance of electromagnetism before special relativity?

I am trying to write a paper on how Einstein's special relativity (SR) essentially saved electromagnetism for high school and am confused on how the following two problems were solved. How did ...
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Are there any descriptions of the reluctance motor invented by W.H. Taylor in the 1800's?

I could not find any descriptions of the first motors of W. H. Taylor in Wikipedia of any reference, history or circumstances surrounding its invention. Apparently the motor was never used for any ...
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Where exactly did George Brown publish the first paper about Turnstile antennas?

In its most basic form the Turnstile antenna is two half-wave dipole antennas that are perpendicular and driven 90 degrees out of phase. For a recent review see Crossed Dipole Antennas: A review (also ...
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What did Einstein learn in his university electricity and magnetism courses?

What did Einstein learn in his university electricity and magnetism courses? Did he learn about such prominent results as Ampère's force law, Weber's force law derived from it (cf. Maxwell's Treatise §...
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Who discovered Maxwell-Faraday equation, $\nabla\times E=-\frac{\partial B}{\partial t}$? Was it Maxwell or Neumann?

I have been trying to find out who discovered Maxwell-Faraday equation, $\nabla\times E=-\frac{\partial B}{\partial t}$. Was it Maxwell himself, or was it Franz Ernst Neumann who derived it? The ...
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During the development of QFT was this theory actually used to build any invention like the MRI?

I have always wondered if the equations of quantum field theory were actually ever used in the production of some invention or device other than needed to make predictions about the Standard Model of ...
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Are Gauss' electrodynamics laws for charge-charge interaction correct at all?

My question refers to a fragment on electrodynamics written by Gauss at around 1835. In this short note (see Gauss' Werke, volume V, p.617) Gauss wrote down a fundamental equation which describes the ...
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Did James Clerk Maxwell derive the permittivity of free space from his "Maxwell's" equations or was the parameter already known by him?

My problem is my lack of knowledge on the historical development of the constant used for the permittivity of free space. I know instead of asking the question I should read Wiki on the history of "...
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What is Heaviside's version of Maxwell's equations?

I have read, in many places, statements like this: Heaviside was able to greatly simplify Maxwell's 20 equations in 20 variables, replacing them by four equations in two variables. Today we ...
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Origin of the Heaviside function?

I have tried to find the actual origin of the Heaviside unit step function and could not. I've searched and searched, read one complete biography of Oliver Heaviside, skimmed another, but nowhere can ...
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How did Maxwell conclude that $\frac{\partial\bf E}{\partial t}$ was necessary to complete $c^2\nabla \times \bf B= \frac{\bf J}{\epsilon_0}\;?$

As we know $$c^2\text{curl}\;\bf B= \frac{\bf J}{\epsilon_0}$$ is incomplete & in many cases like capacitor give contradictory result against Law of conservation of charge. As Feynman writes; ...
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How did Maxwell conclude that light is an electromagnetic wave?

This is a copy of a question I just asked at Physics Stack Exchange. From reading the text on the related questions, it seems that Maxwell equated light with the carrier of electromagnetic force just ...
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438 views

Is it thought that Maxwell used Green's Theorem to derive his equations?

I noticed there are two varieties of Maxwell's equations and although I am not sure which form Maxwell originally worked with and perhaps the differential form came much latter, I was wondering if he ...
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Modification of Newtonian Gravity based on Maxwell's Theory

As is well-known, Maxwell's equations were already consistent with Special Theory of Relativity while the Newtonian law of Gravitation wasn't. It can be shown by solving the equations of Maxwell for a ...
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Why is Maxwell and not Ampère credited for unifying electricity and magnetism?

Ampère, a half century before Maxwell, theorized that magnetism was caused by electrical currents. So, why is Maxwell and not Ampère credited for unifying electricity and magnetism? (cf. the question ...
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What is the idea behind Maxwell's "displacement current" in electromagnetism?

I'd like to get an explanation why Maxwell chose the name "displacement current" for the term $\mu_0\epsilon_0\frac{\partial E}{\partial t}$ he added to Ampere's law (Maxwell's correction). I'm ...
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Why do Maxwell's equations bear his name?

Maxwell's equations in their modern differential form are: $\nabla \cdot \mathbf{E} = \dfrac {\rho} {\varepsilon_0}$ (Gauss's law for electricity) $\nabla \cdot \mathbf{B} = 0$ (Gauss's law for ...
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Did Maxwell originally write his equations using quaternions?

I read somewhere, some time ago that Maxwell originally wrote his eponymous equations using the formalism of quaternions and it was only the later intervention of Gibbs and Heaviside that put them ...
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Who established that $K_e = \frac{1}{4 \pi \varepsilon _m}$?

Coulomb's Law states that : $$F_e = K_e\dfrac{q_1q_2}{r^2}$$ where $q_1$, $q_2$ are magnitudes of the two point charges, $r$ is the distance between them and $K_e$ is Coulomb's Constant (aka ...