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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Names of the electromagnetic units in SI [closed]

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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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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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 ...
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Who originally worked out the magnetic field produced by a solenoid and toroid?

Although, it seems very easy to find the magnetic field produced by a solenoid or a toroid, all we got to do is to make a suitable an Amperian Loop and take the $\mathbf B$ out of the integral and so ...
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What experiment proved that electric current is charge transport? [duplicate]

To my knowledge, neither Volta nor Ampere nor Oersted, the founding fathers of electric current, knew that current is the transport of charge. Who, then, and by which experiment, proved the nature of ...
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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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Was it suspected that the speed of electricity was equal to the speed of light?

Was it believed early on that signals sent via wire moved at exactly the speed of light or simply very fast? Who was the first to estimate the speed? EDIT: Given that they move at less than the ...
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When was spin of subatomic particles other than the electron discovered?

The idea of a spin angular momentum was first proposed in a 1925 publication by George Uhlenbeck and Samuel Goudsmit to explain hyperfine splitting in atomic spectra. At what time was it measured ...
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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 did Gauss and Lagrange derive Gauss law of Electrostatics

On Wikipedia, these two pages are mentioned :Lagrange and Gauss however I am an English speaker and can not comprehend any of the one, can someone provide the translated pages or shortly their line of ...
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How was (non-instantaneous) electric current first discovered?

How was (non-instantaneous) electric current first discovered and what were some of the main first thoughts on it?
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When was the ratio between electric and magnetic forces in an electromagnetic field established?

We know that the magnetic force on a particle moving in a magnetic field was found by J.J. Thomson in 1881, with a slight mistake, and then corrected by Heaviside in 1885 to $F_M = q\,v\times B$. Can ...
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What was the real need of divergence and curl operators?

As I'm advancing my study in Electromagnetism I'm getting introduced to more mathematical operators which are exclusively used in Electromagnetism and Fluid Dynamics only. Let me try to explain ...
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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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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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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 ...