Questions tagged [electromagnetism]

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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Splitting an infinite wire into 2 infinite wires

In this problem if I we want to find the total magnetic field at the center of the loop , If we split this wire from the the point of tangency to 2 wires and calculate the magnetic field of Wire 1 $$...
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Area changes (magnetic flux and Faraday law)

can someone please help me describe the change in the area of the two forms? by the way, if anyone can give here ideas for interesting magnetic flux changes (resulting from changes of the area it ...
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What's making the scenario contradictory to Maxwell's theory of em waves?

I was imagining how an oscillating charge would produce an electromagnetic wave and I got stuck at a point. We know that the direction of propagation of em waves is perpendicular to both the ...
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Does lower temperature increases magnetism of all magnetic material, and to what extent?

Like magnets, reed switch magnetism decreases at higher temperature and increases at lower temperature. This is because high temperatures increase random atomic movement and misalignment of magnetic ...
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Size of the core inside an electromagnet

The equation of magnetic field of a solenoid is as follow: But in this equation the size of the core doesn't take into account ? If so, what is the minimum size that an iron core must have to ...
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Confinement of electromagnetic field in coaxial cable

I wonder about the situation when we apply AC voltage or RF voltage on coaxial cable. Typically, the lateral dimension of coaxial cable is smaller than the wavelength of electromagnetic field in such ...
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Do we need atomic theory to do thermodynamics?

With thermodynamics, systems are studied using macroscopic variables (pressure, temperature, volume, etc.) which do not need a mechanical explanation, which is what statistical mechanics deals with. ...
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Current in an element in lumped circuits

In a lumped circuit where we assume $\nabla \cdot \vec{J} = 0$ at nodes. This could be roughly translated as the nodes don't accumulate charges. Supposedly we connect an element like capacitor between ...
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Can we add some iron nanowires into type II superconductors to improve their performance?

Type II superconductors are widely used in electromagnets because these superconductors can be partially infiltrated by magnetic field. Magnetic field penetrates the material as discrete flux tubes, ...
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Why collisions are necessary for electrical conductivity?

I have a simple question that came to my mind studying the semiclassical electron dynamics: why there must be collisions between particles to have conductivity? If it’s not necessary, what’s the ...
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What happens if we fire a wooden bullet through a magnetic field?

What happens to the bullet and the field if we fire a non-metallic (such as a wooden) bullet through the field beside a bar magnet in a vacuum? Do the field lines move out of the way? Do the field ...
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Equivalent of the geodesic equation for fields

Mass tells spacetime how to curve using the Einstein field equations and spacetime tells mass how to move using the geodesic equation. The effect of the electromagnetic field on space-time is given by ...
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Non-relativistic approximation of the retarded Lienard-Wiechert field

I'm working on a revision of the absorber theory of radiation proposed by Wheeler and Feynman on their paper "Interaction with the Absorber as the Mechanism of Radiation". On page 161 they ...
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What is Lorentz transform purpose abcd [closed]

Lorentz transform was created for: (only one is correct) a) to ensure Maxwell equations are unchangeable b) to ensure time passes equally in all inertial frames of reference c) to ensure ...
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How is energy "stored in an electric field"?

My physics teacher told me the statement "The energy of a capacitor is stored in its electric field". Now this confuses me a bit. I understand the energy of a capacitor as a result of the ...
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Mechanisms responsible for absorption loss in the Ionosphere

I have been given a task at my university of helping with calculating some link budgets for satelites. The work I usually do limits to transmitters and receivers located within the troposphere, while ...
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What does $\sin(a,b)$ mean in the absorber theory of radiation?

I'm doing a revision of the absorber theory of radiation by Wheeler and Feynman (that you can see here: "Interaction with the Absorber as the Mechanism of Radiation" - page 161) and I have ...
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How exactly is electromagnetic radiation the way it is?

Electromagnetic radiation from sun is more likely produced by the nuclear fusion, and at a go radiation is released but how is it possible for different types of radiation to be produced such as, ...
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Relation between Electric Potential and Electric Field Intensity

Suppose we have been given a curve y = V(x) where V(x) represents the Electric Potential at x. Now if for a range the curve is a horizontal straight line, can we say that the Electric field intensity ...
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Different ways to calculate magnetic field of a segment of current [duplicate]

Given a segment of current $I$ of length $L$, we want to calculate $\vec{B}$ on a plane that is perpendicular bisector of the segment. From the Biot-Savart law, $\vec{B}$ depends on $L$ and $R$ (the ...
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Voltage propagation in neurons

Context In the classical theory of passive neurons (where the non linear action potential is not excited), the voltage is successfully described by cable theory. The axon is modeled as a series of (...
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Could intensity be related to the flux of the electric field?

Imagine a cable in which an intensity $\mathbf I$, is passing through. This intensity is caused by the moving particles (for example electrons), going with a certain speed, and with some density of ...
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How can magnetic field lines form non closed loops?

I recently came across this paper "Topology of Steady Current Magnetic Fields", Am.J.Phys (1953) The author points out the erroneous implications of representing magnetic field lines as ...
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The difference between touch and electromagnetic force repulsion

I've read the headline that two things cannot actually touch. Two magnets "touch" each other when they are close enough to make a sound when hitting each other. But they do not touch when ...
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When should I need the constant of integration when I calculate electric potential?

For example, electric potential is given by the formula. $$V = -\int_\infty^a \vec{E} d\vec{l}$$ For some questions, I would just use this formula to get the potential and it would be the correct ...
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Reduced electric field strength in a homogenous isotropic linear dielectric

Griffiths says that for the electrostatic field and electric displacement to work alike, the entire space needs to be filled with the meat of the dielectric, but I'm not sure what he means when saying ...
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How does partialy ionized plasma affect covalent bonds

During partial ionization in plasmas, do diatomic molecules like H2 dissociate into monoatomic states because of the changing states of electron orbitals (exited/ground)?
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Does conservation of charge has anything to do with phase?

I was watching youtube lecture link and professor says that "the independence of that phase leads to conservation of charge" in the following equation. $$\vec{\nabla} \cdot \vec{J} + \frac{\...
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Is there an electromagnetic analogue of thermoacoustics?

I've just learned about thermoacoustic heatpumps. My understanding is that a standing acoustic wave in a tube of gas produces areas of higher and lower average pressure which results in a gradient of ...
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Relation between Radiance and Surface power density (i.e poynting vector intensity)

I am attending a microwave remote sensing course and I have same problem to understand the relation between the radiance and the intensity of poynting's vector. The radiance is defined as: $L(\theta,\...
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Magnetic field inside a cylinder

A magnetically “hard” material is in the shape of a right circular cylinder of length $L$ and radius $a$. The cylinder has a permanent magnetization $M_{0}$, uniform through-out its volume and ...
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NMR for non-invasive blood glucose monitoring? [closed]

This seems like a really promising technology that could have massive implications on the future of everyday health monitoring (monitoring cholesterol, glucose, etc entirely non invasively). What are ...
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Relation between Area under $I$-$H$ hysteresis Loop and $B$-$H$ hysteresis Loop

If the area under the I-H hysteresis loop and B-H hysteresis loop are denoted by $A_1$and $A_2$ (The symbols have usual meaning as set in electromagnetics), then $A_2=\mu_oA_1$ $A_2=A_1$ $A_1=\...
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Can two waves have the same amplitude but different frequencies? [closed]

If the question above is true, how is that possible?
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Why armature is being rotated in DC generator?

I am wondering about why armatures are being rotated instead of being static? The magnetic flux will still cut the armature windings and because of this induced current will be generated. So, why it ...
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How much can we push the plates of capacitor?

I am currently a highschooler and came across this question in physics A capacitor of plate area $A$ and separation $d$ is connected to battery of emf $V$ and is charged to steady state. Now the ...
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Explain this para on electric field? [closed]

Suppose we consider the force between two distant charges $q_1,q_2$ in accelerated motion. Now the greatest speed with which a signal or information can go from one point to another is $c$, the speed ...
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Conservation of a specific type of charge

The Law of Conservation of Charge states that 'the total charge in an isolated system is conserved.' Can we say that total negative and positive charges (individually) in an isolated system is ...
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Mass Spectrometer [closed]

Say, we have a mass spectrometer and we want to determine the mass ratio of Hydrogen and Deuterium. Suppose the ions are positively charged and $q=1.6 \times 10^{-19}C$. The magnetic field can be set ...
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Maximum voltage induced in a coil due to an ac current [closed]

Problem Given a coil of cross-sectional area of $A=0.1 \, \text{m}^2$ in which there is a magnetic field of $10 \, \text{T}$ when there is a current of $I=100 \, \text{A}$ flowing through the wire. ...
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Ampere's law on a finite wire [duplicate]

Consider the circular Amperian loop of radius $r$ in this case. The wire carries a current $I$. Integrating using biot-Savart law gives the field as: \begin{align}B=\frac{\mu_0}{2\pi r}\frac{L}{\sqrt{...
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Modeling ferromagnetic materials in a primitive python FEA

I am working on a primitive 2D DIY magnetic "FEA" solver for a class project. It's really just a big NumPy array where each element in the array can be one of the following: Air Current ...
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How do we get from LHP to RCP on the poincare sphere?

A paper that I was reading wanted to transform the jones matrix of linearly horizontal polarization(LHP) to right circular polarization(RCP). The paper states: Consider... $J_{LHP}\to J_{RCP}$... In ...
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Can the following system work as a perpetual motion machine? [duplicate]

A friend of mine came with this idea ! In the photo ,,we have an external magnet ,and as can be seen in picture ,it shuold interact with the upper magnets( that are similar in design to a padestal fan ...
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The positive and negative terminal of a coil when the flux through it changes [duplicate]

I want to know what will be the positive terminal and the negative terminal of a coil,when the flux is changing through the coil. I know about the direction of the induced current, but wondering what ...
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How to identify north pole of a magnet using only a battery, and a copper wire? [closed]

I have a magnet, a copper wire, and a battery. I need to find the north pole, and the south pole of a magnet using only these items. (not a compass). Here's my attempt: create a circuit, battery is ...
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What is the correct definition of EMF in a circuit?

The EMF $\mathcal{E}$ in a closed circuit $C$ is defined as the closed line integral of the electric field ${\vec E}$ around the loop: $$\mathcal{E}=\oint_C{\vec E}\cdot d{\vec\ell}.$$ But in Section ...
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A doubt about the topic of motional emf from Griffiths

Consider a closed rectangular loop of wire, which is moved to the right with a velocity ${\vec v}$ w.r.t a magnet that provides a static, uniform magnetic field $\vec B=-B\hat{z}$ over a region as ...
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No such thing as electrostatic force

Is it true that there is no such thing as an electrostatic force because all charges are moving relative to each other (there is no absolute rest in our universe) so experience an electric force? ...
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The misconceived difference between the electrostatic and electric force

Some sources are saying that electrostatic (coulombic) and electric forces are the same concept in electrostatics (that is the force that an electric charge experiences in an electric field). While ...
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