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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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How do we know neutrons have no charge?

We observe that protons are positively charged, and that neutrons are strongly attracted to them, much as we would expect of oppositely charged particles. We then describe that attraction as non-...
12 views

Velocity attained by a Loop with an induced current

A rectangular loop of resistance R is kept at a certain distance from an infinite straight current carrying conductor. The current is suddenly switched off. The problem was to find the velocity ...
68 views

In the Stern-Gerlach experiment, why is there a nonzero force even though the atoms were electrically neutral

I know that the magnetic moment of a particle is given by: $\vec{\mu} = \frac{gq}{2mc}\vec{S}$ I know that in the Stern-Gerlach experiment, neutral silver atoms were used. Additionally, the ...
31 views

Explanation on the current circulation in a circuit

I'm studying the electromagnetsim, and I couldn't find a complete explanation on how the current flows in a circuit; I mean, basically, how do I decide whether the current is flowing in or out a node? ...
41 views

What really is an electric/magnetic field?

Have you ever wondered how we can see this field or how it's formed its shape in space? I know we can feel that there's one by its effect which is the force. But what does it look like? We all know ...
19 views

Detecting particles that do not make it through double slits, do observations match those after the slits?

I suppose we have 4 conditions to examine : { single particle | beam } * { with eraser | without eraser } I suppose we have to get the same results that those ...
14 views

Calculation of Lorentz force acting on a volume

Consider a volume $V$ immersed in a magnetic field $\hat B$. Assume that within the volume a current $I$ flows such that the surface density at each surface of the horizontal cross section of the ...
43 views

Electromagnetic waves, displacement currents and capacitors

This is a question from HC Verma’s concepts of Physics Vol 2: Electromagnetic Waves. It’s a question which is a continuation of the previous question, therefore I’ve combined both of them. Q. A ...
28 views

Can EM radiation penetrate through the walls of an aluminium box (Faraday cage)?

What's the best possible frequency to use and is it high frequency or low frequency that has the highest ability to penetrate an aluminium wall?
20 views

How to calculate the RCS (Radar Cross Section) of a sensor tag?

The equation for finding the RCS of sensor tags is given in the following paper. where $S_{21}^{tag}$ stands for the $S_{21}$ measurement taken for the tag in front of a reader. $S_{21}^{isolation}$ ...
55 views

Why aren't primary and secondary coils of a transformer overlapped over each other? [closed]

I am aware that soft iron core present in a transformer does prevent flux leakage. But practically there is some non-negligible flux leakage nonetheless. Why not then just overlap the coils over each ...
13 views

E.M field in a cavity having mirrors : Periodic boundary conditions vs strict periodic boundary conditions

I have a question about how work with modes in a cavity. Basically, why are we allowed to use periodic boundary conditions (and thus plane waves) where in practice the modes are stationnary waves. Why ...
24 views

Strength of Magnetic Dipole

I know magnetic monopoles doesnt exists .And A magnetic dipole always have equal strength. But what about this magnet This is picture of magnet whose thickness is constantly decreasing Will it have ...
31 views

Irradiation at high frequency

I read this statement in Feynman Lecture on Physics (see here for more details): In low-frequency circuits the connection is made with wires, but this method doesn’t work very well at high ...
41 views

Electrical generators: power balance

Usually power generating synchronous generators are rated at around 85-90% efficiency. Curiosity struck me as of how a generator with field coils can ever go to such an high efficiency. My thought ...
46 views

How can a spring contract when magnetic field cannot do work?

When a spring is kept in a magnetic field and current is passed through it, its edges act as parallel conductors and due to the action of Lorentz force, they pull themselves together. A spring ...
24 views

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Does a magnet moving in a uniform electric field experience torque?

Assume a uniform electric field of $E_y$ along $y$ in the lab frame of reference $(x,y,z,t)$. A simple magnet bar is set in motion at $v$ along $x$ in this electric field so that the alignment of the ...
34 views

Variation of phase across the wavefront

I have been going through the theory of diffraction of radio waves when passing through the ionosphere, when I came across the following statement: the amplitude of the wave when it emerges from ...
33 views

Magnetized Steel wire around Soft Iron Core

We all know that a current carrying solenoid of copper is a weak temporary magnet and if we wrap it around a soft iron core it becomes a temporary strong magnet i.e. the iron core magnifies the ...
48 views

Why does the interaction energy for the electric fields of two point charges vanish over any shell smaller than their separation?

A previous question, A triple integral in Spherical coordinates from Jackson's book on Electrodynamics, presents the fairly routine calculation of the interaction energy encoded in the cross-term ...
50 views

Gravitational and Electric Forces in the Movements of Planets [duplicate]

Now that we know about the electric nature of the cosmos, the question arises: "How much are planets affected by electric forces while moving through the universe?" We have been taught that the ...
96 views

A triple integral in Spherical coordinates from Jackson's book on Electrodynamics [closed]

I have been trying a solution for the following integral from Jackson but i do not seem to go anywhere. Please help. The problem is to compute interaction energy due to 2 charges. Compute following ...
27 views

Inductors in Transformers

Why is it the flux change which induces the ac current of primary coil equal to the flux change that primary coil induces on the secondary coil? Is it possible to prove this? slide from video ...
74 views

What does $e$, $i$ and $\vec{p}$ mean in this formula? [closed]

I've found a formula to calculate the $\vec{E}$-field vector of a Hertzian dipole in the far field (don't know if that's the correct term) to draw and simulate the field lines. Link to my source: ...
33 views

How to relate magnetic flux to fluid flux?

I'm trying to grasp magnetic flux as an analogous concept to fluid flux, which is more concrete in my opinion. For example, we can define a vector field $\mathbf{F}(x, y, z)$ which describes the ...
34 views

Magnetism problem

I encountered a magnetism problem requiring me to find out the minimum velocity (along $\hat{\mathbf{i}}$) given to a charged particle so that it passes through the centre of a circular region of ...
15 views

How are the two definitions of B, as magnetic field and magnetic flux density, same?

My question, is primarily, based on this question, in which the accepted answer asserts that $\vec B \,$ has two definitions, As magnetic field$^*$, using Lorentz force \$\vec F=q \vec v \times \vec ...