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.
1
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1answer
46 views
Understanding drift velocities in currents
I have a doubt about the understanding of drift velocities in a current. My problem is that the textbook speaks very loosely about this. It's like: "well, if we apply a field $E$ then the charges will ...
4
votes
2answers
118 views
Cancel out Earth's Magnetic field
Is there any tools except helmholtz coil to cancel out earth's magnetic field to calibrate magnetometers in practice.
1
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0answers
32 views
Back motor effect
Back motor effect is the counter torque which opposes the rotaional motion of the coil in generator.
The back motor effect depends upon the resistance connected to the generator. More is the ...
1
vote
1answer
39 views
Negative emf in AC generator
At a certain instant in AC generator, when the normal of the plane (rectangular coil) makes an angle of 270 degrees with with the magnetic induction B, the value of emf is:
$E = -NAB\omega$
My ...
0
votes
2answers
92 views
Difference between electrostatic and magnetic field [closed]
In this, F (the force set by the field) is perpendicular to the speed of the particle. In which case does F change the absolute value of V? Why or why not?
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0answers
47 views
The electrical field of a conductive sphere containing a charge - gounded vs not grounded
Let's suppose we have a sphere but unlike theoretical ones it'll has have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge ...
0
votes
1answer
92 views
How to design a AC/DC generator and motor? [closed]
Through electrodynamics mechanics learning, it is possible to design a simple and elegant design for the following four machines:
1. AC generator
2. AC motor
3. DC generator
4. DC motor
I have some ...
1
vote
1answer
56 views
Electromagnetic field to cool a substance?
I saw somewhere that an electromagnetic field would cause a substance to let off thermal energy, ultimately resulting in the substance to cool really quickly.
If this is possible, does the strength ...
0
votes
0answers
85 views
Equivalence between a charged rotating cylinder and a solenoid
Suppose we have a cylindrical shell of radius $r$ with surface charge density $\sigma$. Then we start rotating the cylinder at an angular speed $\Omega$. You can show that in this case the surface ...
1
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2answers
68 views
Eddy currents: Explanation of the force slowing down a moving metal plate
Suppose a solid metal plate moves trough a homogenous magnetic field $\vec{B}$ as shown in the following image. You will see that the plate will slow down (as long as not the entire plate is in the ...
1
vote
1answer
45 views
Why electric field outside the sphere that carries polarization is 0?
There is a sphere with radius $R$ that carries a polarization
$$\vec P(\vec{r})=k\vec r$$
$\vec r$ is the vector from the center.
I found electric field the outside generated by the sphere is $\vec ...
0
votes
0answers
38 views
Solution of Maxwell's equation for simple, time-harmonic wire
I would like to compute the electric field $\boldsymbol{E}$ in the time-harmonic case for a (thick) wire parallel to the $z$-axis, but I can't quite get to it.
What I've got so far:
The current ...
1
vote
2answers
301 views
Does a current carrying wire produce electric field outside?
In the modern texts of electromagnetism in the presence of stationary currents the electric field is assumed conservative $\nabla \times E =0 $. Using this we get $E_{||}^{out}=E_{||}^{in}$ which ...
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1answer
82 views
Energy stored in fields
How to intuitively think of energy stored in a magnetic/electric field?
Kindly answer in a bit simple terms without referring to mathematics.
1
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1answer
66 views
Movement of the particle in a magnetic field
This is the numerical question.
A particle having a mass of 0.05 mg carries a charge of $5\times10^{-6}C$. The particle is given an initial horizontal velocity of 5000 m/s, what is the magnitude ...
3
votes
1answer
43 views
Faraday's law for a current loop being deformed
I'm working through Jackson's Classical Electrodynamics text (3rd version, chapter 5.15) about Faraday's law:
Faraday's law is pretty familiar:
$\int_c E \cdot dl = -\frac{d}{dt}(\int_s B \cdot n ...
0
votes
0answers
20 views
Some basic questions about electric field & nucleus [duplicate]
I am not good in physics.You can say I am beginner in this field.
I have some basic questions.
I ju st want to know that
[1] If there is repulsive force between same charges proton-proton then why ...
2
votes
1answer
50 views
Field Tensor and classical limits
I would be very grateful if someone would kindly explain this generalization of the Lorentz force law to the special relativity domain. Please bear with me.
Classically, the Lorentz force law is ...
0
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0answers
56 views
Curie's principle in electromagnetic field theory
I am looking for some explanation and if possible also some references about the applications of Curie's principle in electromagnetic field Theory, precisely in the computation of magnetic (resp. ...
4
votes
6answers
166 views
Electric field near a conducting surface vs. sheet of charge
I know perfectly well how to derive the magnitude of the electric field near a conductor,
$$E = \frac{\sigma}{\varepsilon_0}$$ and near a sheet of charge, $$ E = \frac{\sigma}{2\varepsilon_0} .$$
In ...
4
votes
3answers
226 views
How electricity, and generating electricity works on the atomic level?
I am trying to understand the basics physics as to how electricity works.
Unfortunately it seems most online material is either complex full blown mathematical equations, or water pump analogies.
I ...
0
votes
1answer
47 views
Magnetic induction in solenoid
I found an equation in theory about magnetic induction in a solenoid: $B_s=\mu_0 I n$. It should be magnetic induction for infinite length solenoid. I wonder if this is anyhow useful. Where can this ...
1
vote
1answer
88 views
Retarded time Lienard Wiechert potential
In a potential which needs to be evaluated at the retarded time, is this the time which represents the actual time the "physics" occurred? So $t_{\text{ret}}=t-\frac{r}{c}$, not just because it may be ...
5
votes
2answers
177 views
Effects of a very large magnetic field on the human body
Ever since reading about the NHMFL I have always wondered about this and asked several people without getting a good satisfactory answer. My question is, considering the simplest case let's say a ...
1
vote
0answers
47 views
Fourier Transform of ribbon's beam Electric Field
I have a monochromatic ribbon beam with $E(x)e^{i(kz-\omega t)}$ being the electric field's amplitude. I want to show that the lowest order approximation in terms of plane waves is
...
0
votes
1answer
57 views
Gravity in stone
I want to ask is it possible for a stone to have some magnetic power different from power that we see in ordinary metal magnets (something like earth gravity that attract everything). Someone told me ...
1
vote
1answer
41 views
How do I obtain a sense of scale when thinking about webers?
This Wikipedia article provides a wonderful way to fathom the scale of the tesla. I cannot seem to find a similar set of examples about magnetic flux. I know that the milli-, micro- and nanoweber are ...
0
votes
1answer
61 views
Electric Field in Circular waveguide in TE mode
I know that the magnetic field inside a circular waveguide is
$B_z=B_0\dfrac{\rho}{R}\left(1-\dfrac{\rho}{2R}\right)\cos{\phi}\sin{\frac{\pi z}{d}}$
How can I find the two components of the electric ...
1
vote
1answer
65 views
A good theoretical approximation for a magnetically damped pendulum
In a laboratory course we had to perform an experiment with a pendulum (just an iron weight on a wire) and play around for some time with its wire's length and so on.
This was quite boring and we ...
1
vote
2answers
39 views
Free spin (Curie) Paramagnetism
I'm working through a derivation for Curie paramagnetism and hope someone could help clarify a couple of steps. The way that makes sense to me (although now I have seen the wikipedia derivation below ...
1
vote
1answer
57 views
Power radiated by the sun at different locations
I am wondering can someone help to solve second part which extends first part;
The power radiated by the sun is ${3.9*10^{26}}_{watt}$. The earth orbits the sun in a nearly circular orbit of radius ...
0
votes
0answers
85 views
Equation of motion of charged particle under effect of magnetic field
A charged particle with specific charge q/m diverges from the origin [to the first quadrant] by angle X with x axis and with velocity v. To bring the particle back to the x axis, a magnetic field B is ...
1
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0answers
24 views
Show that the plane of incidence is perpendicular to the surface of reflection
Is it possible to derive from the boundary conditions of the Maxwell equations for E and H, that the plane of incidence for an EM wave is perpendicular to the reflection surface? How? If not, what ...
1
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0answers
37 views
Can someone help me understand this simple derivation for hall voltage?
I have a question regarding the derivation for hall voltage as shown in this image:
How did they get $\Delta V_H = E_H d$ term? ($d$ is the width of the conductor)
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votes
1answer
28 views
2 solenoids: emf and frequency
I'm studying a circuit in AC. I use a function generator and set a waveform.
I have a solenoid and I put a small solenoid inner it.
Could you tell me if there is a relation between frequency and emf ...
-1
votes
2answers
121 views
Do objects have energy because of their charge?
My gut feeling tells me things should have energy because of their charge, like they have energy because of their mass.
Is this possible? Has it been shown? If not then what is missing to make such ...
-6
votes
1answer
55 views
Energy flows in the core also responsible for another of the planet’s unique [closed]
Energy flows in the core also responsible for
another of the planet’s unique features: a
strong magnetic field. Scientists believe that
the earth has had a magnetic field for at
least 3.5 billion ...
0
votes
0answers
23 views
Hitting the target in two different ways [closed]
Electrons are accelerated by an electron gun. As the electrons exit the gun they are deflected by a uniform magnetic field of fixed magnitude $B$ directed into the page. The electrons hit a small ...
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0answers
134 views
Is there any example where electric and magnetic fields are not perpendicular?
Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
0
votes
1answer
35 views
About electrostatic potential energy
I consider an electron (charge $-e$) in $x=0$ and a constant electric field $E(x) \equiv E $. If the electron has initial velocity $v_0$ with the same direction of $E$, then its potential energy is
$$ ...
0
votes
1answer
42 views
Electromagnet, ideal turns depending on ohm
More turns -> stronger field
more turns -> longer copper wire
longer copper wire -> more resistance(ohm)
at what turn does the resistance make the electromagnet weaker? - I want to make an ideal ...
0
votes
0answers
37 views
Can you find the potential between capacitor plates with liquid dielectric in the capacitor's frame? [closed]
A magnetic field B is applied perpendicular to the plates of a capacitor whose parallel plates are separated by d. An electrically neutral liquid of relative dielectric constant k flows between the ...
1
vote
0answers
43 views
Book suggestion : geometric approach to electromagnetism [duplicate]
I´m looking for a book on electromagnetism that is introducing the topic from a geometric point of view, focusing more on the theoretical structure than on the application.
0
votes
4answers
137 views
why is the charge transferred by electrons and not by protons?
charges are transferred by electrons which we all know but why it cant but it cant be transferred by protons.Well i searched on google where i found similar questions already being asked on many ...
0
votes
1answer
55 views
If I have a rectangular loop moving through a magnetic field, which way will it go?
If I have a rectangular loop moving through a magnetic field, which way will it go?
A uniform magnetic field (say it's pointing into the page)
A square/rectangular loop of wire moving into the field ...
0
votes
2answers
273 views
Capacitors and resistor in series and in parallel [closed]
In this circuit, are $R_1$ and $C_1$ in parallel and $C_2$ and $R_2$ in series?
I have think that the currents that flows trought $R_1$ isn't the same that flows trought $C_1$ so, $R_1$ and $C_1$ ...
2
votes
1answer
52 views
Given expectation values for E and B, can you find an associated state?
When we quantize the electromagnetic field, we develop the concept of the field operator $A(\vec{r},t)$ and the simultaneous eigenstates of momentum and the free field Hamiltonian (i.e., each ...
2
votes
1answer
70 views
Properties of the Faraday tensor for constant fields
I'm doing a special relativity past exam paper and have got caught up with something that I hope someone can help me with!
I have to show that for constant fields, the magnitude of A, the ...
3
votes
1answer
97 views
Fermi level with Landau levels
So my question is regarding where the Fermi energy is when you have 2D electron gas in an applied magnetic field. My book explains that, using the Landau gauge, you find that the 2D density of states ...
0
votes
0answers
39 views
Magnetic field at a point [closed]
Find the magnetic field near a straight current carrying conductor of Length $L$ and current $I$, at point located along the perpendicular bisector of the wire a distance $r$ from the wire. Show all ...
