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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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
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1answer
38 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 ...
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2answers
88 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
44 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 ...
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1answer
83 views
Force of electromagnet on piece of iron
I can find equations to give the force of an electromagnet on a piece of iron when the iron touches the electromagnet.
But what about when the iron is some distance from the electromagnet? ...
0
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1answer
81 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 ...
0
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1answer
45 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 ...
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2answers
360 views
How does the electric motor and generator vary?
what is the key difference between the windings of the electric motor and electric generator?
2
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2answers
71 views
continuity of the electric potential due to a surface charge
The Electric potential due to a charge distribution on a surface is :
$\Phi \left ( x \right )=\int \frac{\sigma \left ( {x^{}}' \right )dx{}'}{\left \| x-x{}' \right \|}da$ I want to show that it's ...
4
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3answers
223 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 ...
1
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1answer
111 views
Transformators (primary and secondary windings)
Consider the following problem:
Robby wants to put a light in the shed so he puts a cable between his house and the shed. In the cable there are 2 wires with a combined resistance of $0,92 \space ...
1
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1answer
40 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 ...
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0answers
81 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 ...
0
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1answer
53 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 ...
0
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1answer
495 views
Coil design and magnet orientation in a unique generator
First, I am not an electrical engineer - I am a hobbyist building a prototype linear-stlye generator based on an idea I had which, for various reasons, cannot be built with magnets that pass ...
1
vote
1answer
65 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 ...
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0answers
35 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 ...
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 ...
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0answers
55 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. ...
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0answers
38 views
Electromagnetism [closed]
I am about to take a course on electromagnetism at my university. Can someone please tell me sort of a bird-eye view of what this course is all about? And what I'm expected to come out learning from ...
1
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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
...
2
votes
3answers
672 views
How to make a small tokamak?
$\require{mhchem}$I made a fusor once, like the easy science project: deuterium-deuterium ones, but they're really inefficient. I was wondering if it would be possible to make a small tokamak; not one ...
-5
votes
0answers
52 views
Could anyone help me to interpret the wave geometrically? [closed]
This is the problem:
A 180-MHz wave travels in medium characterized by $\mu_r = 1$, $\epsilon_r = 25$, and $\sigma = 2.5$ mS/m. The electric field intensity is given by $\widetilde{E} = ...
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1answer
45 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 ...
6
votes
0answers
97 views
Nuclear Magnetic Resonance (NMR) Conceptual Questions
Let $M$ be the magnetic moment of a system. Below are the Bloch equations, including the relaxation terms.
$$\frac{\partial M_x}{\partial t}=({\bf M} \times \gamma {\bf H_0})_x-\frac{M_x}{T_2} $$
...
6
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7answers
3k views
Electromagnetic fields vs electromagnetic radiation
As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same ...
3
votes
2answers
4k views
How do you magnetize an object?
How can I go about magnetizing something? Specifically, a whole bunch of BB's. I want to try this so that I could make a cheaper version of the Bucky Balls product. Even if I can't replicate Bucky ...
1
vote
1answer
124 views
Relationship between gauss and decibels
In my ongoing effort to understand the world around me, I want to wrap my head around the relationships between two units of measure. Specifically gauss and decibels.
The quandary comes from my ...
0
votes
1answer
56 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 ...
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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 ...
1
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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 ...
1
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1answer
64 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 ...
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0answers
81 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 ...
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1answer
53 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 ...
1
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4answers
309 views
No magnetic field from a static charge - Is there a simple physical argument to show why?
For a charge moving in an electric field $\vec E$, its equation of motion is given by the electric part of the Lorentz force $$\frac d {dt}\gamma m \vec v = e\vec E$$This comes from the conservation ...
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4answers
133 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 ...
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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 ...
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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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2answers
120 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 ...
3
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3answers
1k views
What is magnetic conductivity?
I searched google for the meaning of magnetic conductivity but couldn't figure out what is it?
electric conductivity is usually means that there is the electric field parallel to the interface is ...
-6
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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 ...
3
votes
2answers
123 views
Why is there a factor of 1/2 in the interaction energy of an induced dipole with the field that induces it?
In this paper, there's the following sentence:
...and the factor 1/2 takes into account that the dipole moment is an induced, not a permanent one.
Without any further explanation. I looked ...
0
votes
2answers
82 views
What would result in a transformer that has its secondary wires disconnected from any circuit?
I am studying magnetism and I am curious as to what happens in a transformer that has its secondary output wires connected through a circuit versus one that doesn't.
My main questions (in the case of ...
0
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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 ...
2
votes
1answer
195 views
Electrodynamics and the Lagrangian density
Could anyone tell me what equations can I obtain from the Lagrangian density
$${\cal L}(\phi,\,\,\phi_{,i},\,\,A_i, \dot A_i,\,\,A_{i,j})~=~\frac{1}{2}|\dot A+\nabla\phi|^2-\frac{1}{2}|\nabla \times ...
0
votes
1answer
35 views
About electrostatic potential energy
I consider an electron (charge $-e$) in $x=0$ and a constant electric field $E(x) \equiv E $. If the electron has initial velocity $v_0$ with the same direction of $E$, then its potential energy is
$$ ...
0
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3answers
261 views
Divergence equations (Maxwell)
Let $\mathbf{E}(r,t),\mathbf{B}(r,t)$ be two vector fields (in $\mathbb{R}^3$), s.t. they satisfy fot $t=0$ the equations:
$\nabla \cdot \mathbf{B}(r,0)=0.$
$\nabla \cdot ...
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2answers
360 views
What is the force between two perpendicular wire? [closed]
What is the force between two perpendicular wire carrying current, one to the north and one to the east?
2
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2answers
107 views
Power due to dipole radiation and time reversal symmetry in classical E&M
The dipole formula for the power loss emitted by a time varying electric dipole is (in natural units) $P = \frac{\dot d_i^2}{6 \pi}$. This is clearly even under time reversal symmetry $T$, but a ...
0
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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 ...
