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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Feynman's statement about the importance of basic science

I remember reading in the line that Feynman saying if the best technicians were tasked to build a radio they would make longer and thicker cables and transfer message but it took a physicist to ...
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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 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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Difference between Perrin's and J. J. Thomson's experiment

In J. J. Thomson's paper (Phil. Mag. S. 5. Vol. 44. No. 269. Oct. 1897) concerned with cathode rays, Thomson writes, that the experiment by Perrin that supposedly proves that cathode rays are made of ...
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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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How did Henry Cavendish deduce the inverse square law in electrostatics from his experiment in 1772?

An elegant experiment in 1772 by Henry Cavendish. Cavendish charged a spherical conducting shell that contained within it, and temporarily connected to it, a smaller sphere. The outer shell was then ...
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How was it discovered in the 19th century that electric or magnetic forces were not instantaneous?

Marc Lange writes (page 29) It was known by about the 19th century that any action at a distance involving electric or magnetic forces would be retarded and so undermine not only spatial locality, ...
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Who introduced concept of capacitance matrix

We know of two ways of representing voltage-charge relations of an assembly of conductors: $V_j=\sum P_iq_i$ and $Q_j=\sum C_iv_i$ Who introduced these equations for the first time and though one can ...
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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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Why is electric dipole moment represented by “p”?

"I recently came across a text where the electric dipole moment was represented as "d" instead of the more commonly used "p". The reason behind using "d" here is probably that "dipole moment" begins ...
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How on Earth did Ampere come up with Ampere's circuital law?

When I asked for proof of Ampere's circuital law I learned that this law itself is taken as an axiom. Okay I just need to know how did he come up with such a law? how to confirm that result ...
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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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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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Charge concept before discovery of electron [duplicate]

How did the concept of positive and negative charge originate before the discovery of an electron? My question is related to the historical aspects.
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What were the 3 critical experiments and the argument given by Ampère which helped in determining the magnetic field made by electric current?

In The Feynman Lectures on Physics volume 2, Magnetostatics, section 13-4 Mr. Feynman tells us that there were "three critical experiments and a brilliant theoretical argument given by Ampère" that ...
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How did Reginald Fessenden realize that spark-gaps could generate waves and the modulation of those waves with voice?

I can somewhat understand how the spark-gap was devised to transmit waves and how the waves were first measured in frequency but what lead to the idea of "modulation" where another electrical signal ...
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How did people measure electric charge at the time of Coulomb?

Around the time that Coulomb gave Coulomb's law, how did people measure electric charge?
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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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How did early scientists know if a current was changing direction? (AC vs. DC)

How did Faraday, Ampere and Hippolyte Pixii know that electricity 'traveled' at all? Let alone in a certain direction? And that it was reversing direction with certain early generators?
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Why is the amount of charge needed to generate 1 unit of electric flux, called permittivity?

This keeps confusing me. I keep imagining "permittivity" as being "The ability for a substance to permit electricity", when it is the opposite. High permittivity means it is hard (requires a lot of ...
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How did people in pre-Ampere period deduce this?

How did people before Ampere (eg-Coulomb) who used magnetic-pole model, know that only two surfaces (north and south poles) of a bar magnet exerts and experiences force while the rest of the surfaces ...
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Was the telegraph system of 1859 powered by AC or DC and how extensive was it?

I was actually curious how the Solar Coronal event of 1859 known as the Carrington Event affected the telegraph system. Wiki does not seem to have much detail of this but there is mention of it in a ...
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Historically how it was discovered that we need fields to describe matter?

This question is from one historical perspective. The question is: how physicists historically found out that one needs quantum fields to describe matter? Being more detailed. Let us consider the ...
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Several questions about Gauss's contributions to electromagnetism

First of all, i appologize if i'm asking too many questions about Gauss (and some will also say "not very interesting questions"); i know i might appear ridiculus - but i really think it's an ...
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Is Gauss's electrodynamics law for inertial motion correct at all?

My question refers to a fragment on electrodynamics written by Gauss at around 1835. In this short note (see Gauss's Werke, volume V, p. 616-617) Gauss wrote down a fundamental equation which ...
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Is there an anthology of classic papers on electricity?

I'm trying to find a book similiar to Stephen Brush "Kinetic Theory of Gases: An Anthology of Classic Papers With Historical Commentary". The electricity version, let's say! I like to see how subjects ...
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Who first noticed that the radiation pressure formula $p=U/c$ agreed with $E=pc$ from special relativity?

Does anyone know behind stories? As it seems that $p=U/c$ was known before the advent of special theory of relativity, (Halliday, Resnick, Walker says that Maxwell derived this.) when $E=pc$ was first ...
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Introduction of magnetic vector potential [duplicate]

Who first introduced the concept of magnetic vector potential and why? Was it introduced only for ease of mathematical calculation or it was done keeping in mind its physical significance like ...
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How did Milikan know that oil drops would acquire only few electron charges?

In the book of Experiment in Modern Physics, by Melissinos, at page 2, it is given that: 2. The Millikan Oil Drop Experiment In 1909, R. Millikan reported a reliable method for measuring ionic ...
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Capacitance or capacity?

In physics, the capacitance of a conductor is (roughly) the net charge accumulated when it is grounded relative to a unit voltage at infinity. The same quantity comes up in mathematics, but we call ...
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Who originally derived the general force law equation of force between current elements?

Wikipedia credits this to Maxwell. This derivation can be found in Maxwell's Treatise on Electricity and Magnetism vol. 2, part 4, ch. 2 (§§502-527). I went through the derivation and found two self ...
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Who was the first to use the term field in physics?

Faraday, after drawing his lines of force in 19th century, is normally credited as the first to use the term field in physics. But... ... was not the term field used in the context of gravitational ...
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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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When Was Kaluza-Klein Theory Appreciated?

As far as I understand, the Kaluza-Klein theory, despite its unprecedentedly profound and beautiful character, had a modest following in its early days. I guess that two of the many reasons might be ...
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What/When was the first radio nav system capable of triangulating your position?

What was the first radio navigation system capable of triangulating your position, and when was it built? How accurate was it and what was its range? This does not have to be GPS or a satellite ...
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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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History of Magnetism before the Hubbard model

I'm interested in models used before the Hubbard model (free electron model, band model, etc, both itinerant and localized models). What were their strengths and weaknesses? Which model is currently ...
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“Tension” between Electromagnetism and Newton's laws

When talking about the inconsistencies in physics that led up to Einstein's discovery of relativity today's professors always say that Maxwell's discovery of the constant speed of light $c$ created a ...
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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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Was the pre-special relativity discussion a hot topic in the late nineteenth and early twentieth century?

We know that low-dimensional materials and topological materials are some of the current hot topics in Physics. Did this happen with the pre-special relativity discussions in the late nineteenth and ...
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Why are capacitors and inductors called that way?

I do understand that electrical resistance describes somehow the material resistance to electrons flow but I don't see the meaning behind the names capacitors and inductors (if there is any and it ...
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Electromagnetic constants and the speed of light

Was it known before Maxwell's time that the vacuum permitivity was inversely related to the permeability by a factor of $c^2$?
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Who was the first to invent the induction motor?

I have heard that Galileo Ferraris and Nikola Tesla invented the induction motor independently. Does anyone know who was the first and were they similar in power output and design? This may be a ...
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When was the electronvolt first introduced?

When was the unit "electronvolt" (eV) first introduced, and by whom? The definition of the eV requires the knowledge of the electron charge $e$, so it must have been introduced after 1909, the date ...
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Abraham's electromagnetism book and its story

Max Abraham is well known for his electromagnetic mass theory, and his book Theorie der Elektrizität is said to be read widely around 1900. I am trying to find this book, but the editions look like a ...
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Who first discovered and produced an alternating current?

What physicist first discovered or produced an alternating current and recognized it as such?
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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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Why is one of Maxwell's equations named after Ampère? Who first named it after Ampère?

Ampère never wrote down what is confusingly called "Ampère's circuital law," not even the form without the displacement current term, as Ampère never dealt with the field concept.* Maxwell derived $$\...
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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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Where in Gauss's works does he derive “Gauss's Law”?

Where in Gauss's works does he derive "Gauss's Law"? Or is "Gauss's Law" named after Gauss for a different reason?