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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Magnets quantum locking/levitating [duplicate]

How does cooling a magnet allow it to quantum lock/levitate? I have seen it in videos but do not know how it works.
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49 views

Are magnetic field lines level sets?

I have been learning a bit about level sets. After doing this, I looked at a diagram of magnetic field lines and noticed they don't intersect rather like the lines on closed curve level sets. My ...
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2answers
49 views

Why does a voltmeter give a positive reading for a path in the same direction as the electric field?

Straight from my textbook: If the direction of the path from initial location to final location is the same as the direction of the electric field, the potential difference is negative. Yet a ...
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1answer
29 views

In a noiseless environment, how accurate do today's transmitters send EM waves?

Suppose that there is no external noise in the environment. How accurate are today's TEM wave transmitters in such a case? So if we want to send $200\cos(1000\pi t)$, can transmitters send exactly ...
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1answer
67 views

Charge of a moving particle [duplicate]

Is there an experiment that measures the electric charge of a moving particle, therefore proving "experimentally" that it is indeed the same as a static particle?
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1answer
39 views

The force on the northern hemisphere

I am reading Griffiths' Introduction to Electrodynamics. On page 364, example 8.2 (4th edition), he calculates the force on the northern hemisphere of a ball with total charge $Q$ spread uniformly. ...
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1answer
30 views

Induced electric field

Let's consider a thin cylinder of radius $r$ with a charge in is outer surface. It is made of an isolator. Let the magnetic field be parallel to its axis. If the magnetic field changed by $dB$ in time ...
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1answer
67 views

How does an infrared thermometer actually calculate temperature?

I am slightly confused about infrared radiation and the equations related to it. $P = A \epsilon \sigma T^4$ (1) and $B_{\lambda}(\lambda,T) = \frac{2hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda ...
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84 views

Maxwell's equation in curved spacetime - how come? And experimental evidence?

I'm trying to understand the generalization of Maxwell's equations to curved spacetime. In FLAT (Minkowski) SPACETIME: If we define the "four-potential" as $$\ ...
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2answers
41 views

Does the gravitational force of one object interfere with that of another?

Assume we have two iron spheres, Sphere A and Sphere B, with identical masses floating in the vacuum of interstellar space separated by some distance from each other. The gravitational force of each ...
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1answer
69 views

Magnetic moment of an iron-core solenoid

I'm currently developing a Simulink model for the attitude control system (ACS) of an undergrad-developed CubeSat. The ACS uses magnetorquers for attitude actuation. The magnetorquers are iron-nickel ...
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2answers
62 views

Path of a proton in a magnetic field

I read somewhere that a proton takes a semicircular path and exists a magnetic field when it enters. I did some research and that seems to be the case. From my understanding, an electron in a magnetic ...
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1answer
81 views

Why does Ohm's law ignore the Lorentz force?

For example, the usual derivation of the complex dielectric constant of metals (using the Drude model) makes use of the Ohm's law in the Maxwell's equations, but what is never mentioned is why they ...
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98 views

Gravity vs. Electromagnetism Scenario

Imagine a two dimensional world where there are only two electrons. They are set right beside each other. Of course, immediately they will start to separate, being repelled. My question is, as they ...
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47 views

How to repeat the Biot-Savart experiment for the direct current in a straight wire and the corresponding magnetic field without side effects?

As I read Biot and Savart took a compass needle and this needle make some rotation when the current was switched on and off. As it was clear that a changing current induces a magnetic field the ...
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1answer
42 views

Are the electrons spin and his magnetic dipole moment unambiguously connected?

Is the angle between the spin orientation and the magnetic dipole orientation for all electrons and under all circumstances the same?
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16 views

Expanding the H and D field in orthogonal modes

Currently I am doing my bachelor thesis on the behaviour of Q-factors in 3D microwave cavities. One step in that process is to approximate the behaviour of the 3D cavity by comparing the cavity to an ...
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1answer
38 views

Interference and windows

The other day i was learning about interference patterns with the effect of a bubble making a rainbow on the surface. I learned that the reflections from both sides of the soap can interfere ...
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13 views

Electromagnetism Books and Lectures [duplicate]

I am an undergraduate at mathematics.And this semester i took E&M as one of my courses because i found it interesting .So i am looking for a good introductory book that will keep my interest as ...
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2answers
76 views

Obtaining electric field of an uniformly charged sphere surface without using gauss law [closed]

How can i obtain the electric field due to a uniformly charged sphere surface without using gauss law on a point outside the sphere, im stuck not knowing what infinitesimal surface i shall consider so ...
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90 views

Force between two current carrying wires: the general case

Assume two straight current carrying parallel wires with currents ($I$ and $I'$) flowing in the same direction, at a distance $R$ from each other. From Ampère's law (and from Biot-Savart as well) it ...
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2answers
73 views

What actually is a continuous charge distribution? [closed]

I am well aware of the maths of how to do all sorts of calculations using continuous charge distributions (like volume, space, and, line charge distributions) but when I think about it I couldn't get ...
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22 views

Accurateness of measurement of 1Ampère for the last years, especially depending from the method how to switch on the current?

From Wikipedia: Ampère's force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ...
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1answer
31 views

How does the Hutchinson Effect work? [closed]

I have seen pictures online of metal ripped apart and metal completely messed up due to the Hutchinson Effect. How does this effect work and what are the other principles behind it?
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1answer
46 views

Electron propagation

How can electrons travel in these beams if they repel?
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49 views

How does the magnetic field generated from a rectangular cross-sectional current-carrying conductor differ from a circular cross-sectional conductor?

I can find much information of cylindrical conductors (ie. regular wires), where $B=\frac{\mu_0 i}{2 \pi r}$ and $r$ represents the radius (or distance) from the centre of the conductor, however I ...
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1answer
64 views

Why particles don't lose mass when they radiate

Charged particles radiate when accelerated: in the rest frame of the particle moving with acceleration $\textbf{a}$ the amount $dW$ of radiated energy over time $dt$ is $$ dW \propto \textbf{a}^2 ...
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34 views

Explanation for: A monopole antenna must contain a resistor (or equivalent) and therefore must have 2 terminals?

Could someone explain why this sentence makes sense: A monopole antenna transfers energy from electrical domain to the electromagnetic domain, hence must contain (equivalently) a resistor, hence ...
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Reference for the Definition of Magnetic Properties [duplicate]

I am writing a report on a piece of software I have made as part of my final year assessments. The software models the flux density of arbitrary arrangements of permanent magnets. The readers of my ...
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36 views

Speed of light in a medium as superposition of dipole radiation

Studying electromagnetism I know that the speed of light in a medium is $v = c/\eta$ and that it's possible to derive this from the Maxwell equations in the medium. But I wanted to find a microscopic ...
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1answer
57 views

What is the difference between a magnon and a spinon?

For a long time, I thought the terms "magnon" and "spinon" were equivalent, describing the collective spin excitation in a system. Lately, I have seen remarks in the literature that they indeed do ...
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23 views

How to generate a Hysteresis curve using MOKE?

I am designing an online lab to generate Hysteresis curve using the principles of MOKE (Magneto Optical Kerr Effect) Is there any math or a logic that I can use to generate the Hysteresis curve? ...
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0answers
25 views

What are some good online texts for electromagnetism? [duplicate]

I am trying to gain a basic knowledge of electricity and magnetism. The resource being free/cheap is important, because I am still a high school student and don't have much money to spend on books.
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1answer
36 views

Proof the directivity antenna formula in degrees

For a single-lobed pattern the beam solid angle is approximately given by $$\Omega_A \approx HP_E.HP_H$$ where $HP_E$ and $HP_H$ are the half-power beamwidths in radians of the main beam in the E ...
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1answer
192 views

Charged particle under a uniform electric field

Suppose a charge particle $q$ starts to move without initial velocity under the influence of a uniform electric field $E$ pointing in the positive $x$ direction. Express its position vector in ...
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Carnot cycle efficiency increases by which method either increase sink temp. or decrease source temp

which method is more suitable for increasing efficiency of Carnot cycle engine either increase sink temp. or decrease source temp.?
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1answer
57 views

Magnetic field and electric field induce one another forever [duplicate]

A changing electric field produces magnetic field and vice versa. Does that mean that this process will carry on forever? Think of a circuit with a capacitor. The magnetic field due to the current at ...
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1answer
29 views

What is the force on a moving charge in combined magnetic and electric fields, in general, when the magnetic field defines the z-axis?

This is a question from a problem sheet. How am I supposed to find the force applied to a moving charge by magnetic and electric fields when the question only gives me the magnetic field $B=B_z \hat ...
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1answer
87 views

Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on ...
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3answers
620 views

Would a spinning, evenly charged sphere generate a magnetic field?

I could see how it would go either way. On the one hand, there IS moving charge; on the other hand, it is not discernibly moving.
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2answers
49 views

Is there an electric field due to current?

Is there any electric field associated with current? If yes, then charge particle passing through magnetic field due to current should also experience electric force along with magnetic force.
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1answer
84 views

Why is gravity viewed as a curvature of spacetime and not the electromagnetic force? [duplicate]

There are four known forces in the universe. Two of these forces are the force of gravity and the force of electromagnetism. The first is the result of the mass of the object that has the gravity. The ...
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54 views

Why is the electric field inside a solenoid tangential?

I have been looking at some derivations for the electric field inside a solenoid. I know how to find it, but I don't get the symmetry argument used. This is often of the form: Since if we choose ...
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0answers
11 views

Can TEM waves have constant offsets - that is, mean of non-zero in context of Poynting's theorem?

Suppose the electromagnetic wave and the corresponding magnetic field wave are TEM waves. Can such waves have overall mean of non-zero? (so DC offset) If they do, what do they mean in context of ...
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1answer
90 views

Finding Magnetic Field in loop of wire in semicircle [closed]

This is the problem I'm working on: A loop of wire has the shape of two concentric semicircles connected by two radial segments (See figure). The loop carries a current $I = 280.00 A$. Find the ...
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1answer
55 views

What do we mean with magnetic monopole and dipole?

What do we mean with magnetic monopole and dipole? I can not find a way to relate magnetic monopoles and dipoles with electric ones. I do not understand their outcomes. Also,what is their role in ...
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1answer
54 views

Induced potential difference paradox

So,i was studying from some lecture notes from MIT's open course program,and i stumbled across this example The example says:The solenoid is so long that its external magnetic field is negligible. ...
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2answers
53 views

Induced emf problem

This is not homework question,just a thought experiment about a general question i have about induction. Let's suppose that we have a closed circuit with only two resistors in series.We also have a ...
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Induced EMF question. Not sure what I'm doing wrong. [closed]

The question: A circular conducting loop of radius 17.0 cm is located in a region of homogeneous magnetic field of magnitude 0.100T pointing perpendicular to the plane of the loop. The loop is ...
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1answer
39 views

Why is it possible to define a potential difference in a wire that carries a steady current?

My book introduces $\nabla\times E = 0$ as the condition for an electrostatic field, which is what makes it possible to define a potential difference between two points. As far as my present ...