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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2
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2answers
90 views

Why do similar smooth metals seem to stick together?

We have a stack of thin (0.025in) stainless steel plates (round 2in)that seem to stick together. Surfaces are clean of oil/grease, and when we lift the top piece off the stack with a suction cup, the ...
0
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3answers
73 views

What is the voltage at every pair of points along a ideal wire that is connecting the two terminals of a battery?

If you stick a wire across a battery, obviously it is going to discharge the battery. This will be due to a voltage difference between the two terminals. However, the equation $V = IR$ tells you how ...
2
votes
2answers
85 views

Force between two point charges moving parallel to each other

When we observe two point charges moving parallel to each other we can see two forces acting on each of the charges: the Coulomb force the magnetic force ($\mathbf{F}=q\mathbf{v}×\mathbf{B}$) ...
1
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1answer
18 views

Relation of resistance between two metals and capacity

My schoolbook goves the resistance between two metals in a material with conductivity $\sigma$ as $R=\frac{\epsilon_0}{\sigma C}$, but they don't show how they got this result. Can someone show me how ...
1
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1answer
37 views

How does Kohn's theorem demonstrate that a rotating microwave field can only connect the ground state with the cyclotron mode?

This is a follow-up question to Proof of Kohn's theorem. I am confused about a point in the answer given by @NowIGetToLearnWhatAHeadIs. It is noted that the perturbing Hamiltonian in Equation 12 ...
0
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2answers
136 views

What will happen when lightning strikes on the surface of the deep sea?

The lightning is having enormous amount of energy, as it strikes the ground it makes various electrical and magnetic effects. If the lightning strikes a tree, that will be burst by lightning. ...
0
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0answers
30 views

By what mechanism is back-emf induced in a railgun?

I don't see what causes a back-emf in a railgun, because as the projectile moves along the rails, there is no change in field on any part of the projectile. Therefore, there shouldn't be any back-emf, ...
12
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5answers
5k views

Why doesn't this magnetic perpetual motion machine work?

I know that this machine does not work, via thermodynamics. I am asking for an analysis in terms of mechanics and magnetism. Anyway, so here is the machine: The magnet (the red ball) pull the ball ...
0
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0answers
25 views

Conductors - force needed to maintain a constant velocity

There runs a current $I_0$ through a straight and long conductor. Two more conductors are placed parallel to it in a plane with distances a and b respectively. The resistance of the connection is ...
1
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0answers
22 views

How can I have a voltage in hall effect with zero magnetic field?

How can we obtain a voltage with no magnetic field is applied to the semiconductor? They told me that if the points where I measure the potential difference are not at the same level I would obtain a ...
0
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0answers
38 views

EM wave frequency vs. attenuation

Why does increasing frequency of an EM wave (for example in sea water with positive and negative ions floating about) increase the attenuation of the wave? Is the relative permittivity changed or the ...
0
votes
1answer
108 views

NOT Perpetual Motion; Could It Work?

TL;DR The energy is not being created freely, so why shouldn't it work? We have all seen the YouTube "perpetual motion" machines. You know, the computer fans with magnets taped on them and hidden 9 ...
0
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0answers
29 views

Flux cutting in a uniform magnetic field

Say we have a uniform magnetic field acting into the page, and we have a bicycle wheel which is spinning at a constant tangential velocity $v$. Each spoke has a equal length, $l$. Reading has told me ...
0
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3answers
93 views

Where are the poles in a magnetic field generated by a current carrying straight conductor?

Consider the magnetic field generated by a straight current carrying conductor. Where are the poles?
1
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0answers
31 views

Magnetic forces [closed]

Can we generate magnetic field forces for pushing or pulling devices? How much weight can be pulled by electromagnetic field?
0
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0answers
57 views

How to properly implement Huygen's integral?

I'm really confused by what's happening ... I'm trying to propagate a beam some distance and compare initial and final intensities. Lets say the initial electric field is just cos(200x). I then used ...
0
votes
2answers
32 views

Change of magnetic flux on size of magnetic field and area

Consider a solenoid with 50 turns. Each turn gives has an area $A$. When the power is switched on, each turn produces a magnetic field of 1 Tesla. What is the total change in magnetic flux when the ...
0
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0answers
67 views

What is the cause of the time-varying electric and magnetic near-fields around a wire with a 60Hz AC current?

I know that it's the accelerating electrons in an AC current that are the cause of far field effects. But, what about the reactive near field close to a wire that has a 60Hz AC current? What is the ...
0
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3answers
62 views

How to decide if a potential is a scalar?

I know that ${\vec E}=-{\vec \nabla} V$. If a potential is scalar, I can find its electric field strength. The question is how can I know if a potential is scalar? Do all point charges result in ...
1
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0answers
29 views

Boundary conditions for vector wave equations

Assume the time-harmonic case of Maxwell's equations, one can obtain the following vector wave equations: $$ ...
0
votes
1answer
73 views

How many coils of a wire in an electromagnet would make 100 milliTeslas field? [closed]

This is a rather stupid question. I'm making a basic electromagnet using copper wire and an iron nail and need to make an electromagnetic feild roughly about 100 milliTeslas . Ill be using a gauge 6 ...
0
votes
1answer
21 views

What is the intensity distribution behind the first beam splitter on an observation screen at the same distance like behind the second beam splitter?

Mach-Zehnder interferometer has been used, among other things, to measure phase shifts between the two beams caused by a sample or a change in length of one of the paths. My simple question is: What ...
0
votes
2answers
83 views

Why can't LIDAR be implemented with traditional antennae?

In robotics, LIDAR and RADAR are both used for obstacle detection. The data they produce are very similar, but they do have different qualities (LIDAR is more precise but less robust). There are many ...
1
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2answers
49 views

Total angular momentum of electron in a magnetic field

In this question: Electron in the proximity of a magnetic monopole It is stated that for an electron in the magnetic field of a monopole, $ \vec{B}(\vec{r}) = \frac{g}{r^3}\vec{r} $ , that the ...
0
votes
0answers
10 views

Image charges for currents?

I am struggling to get my head around a problem involving creating a transmission line using a wire of radius $a$ in a vacuum a distance $d$ above an infinite grounded plate ($d \gg a$). I wish to ...
4
votes
5answers
282 views

How does electricity produce magnetisim?

I am in class 10 and I have just read the electromagnetism chapter. They always keep on saying that electricity produces magnetism! but how!? We know electrons move, but how do they produce something ...
0
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0answers
28 views

Calculating current on power line from induced voltage on nearby loop

The question I'm having trouble with is: A small circular loop of 5mm radius is placed 1 meter away from a 60Hz power line. The voltage induced on this loop is measured at 0.6 microvolts. What is the ...
2
votes
2answers
66 views

Units of vector differential operator del ($\nabla$)

My book says that $\left[\nabla \cdot (\vec E \times \vec H)\right] = \mathrm{W/m^3}$. I see that $\vec E$ is in $\mathrm{V/m}$ and $\vec H$ is $\mathrm{A/m}$, so these multiplied is $\mathrm{W/m^2}$, ...
0
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2answers
94 views

Do all the things have a magnetic field?

I search for this but there is no answer for this question! Do all the things have a magnetic field? And also gravity ? Can you answer?
0
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0answers
39 views

Does the length of a bar magnet matter in producing EMF?

Consider the following diagram. There are 3 apparatuses to produce EMF. The coils are identical in cross section area, the number of winding, and length. The bar magnets have the same cross section ...
0
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1answer
39 views

Infinite, straight, current-carrying wire uniformly charged to a negative electrostatic potential

I am working on a problem that states the following: Imagine an infinite straight wire carrying a current $I$ and uniformly charged to a negative electrostatic potential $\phi$ I know here ...
1
vote
2answers
51 views

Why does electrical impedance have as many parameters as it has?

The impedance of a circuit is written: $$ Z(R,L,C,f) = R + j ( 2 \pi f L - \frac{1}{2 \pi f C} ). $$ What is the line of thinking that frequency, resistance, capacitance, and inductance are the only ...
0
votes
1answer
37 views

EM waves in conductors

On a recent test in my E&M class, we derived what happens to an EM wave propogating in a conductor of conductivity $\sigma$, but I'm having trouble understanding the results. We started from the ...
0
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0answers
35 views

Electron's Frame Aharonov-Bohm Effect

In the electron's inertial frame the solenoid moves past it in the Aharonov-Bohm Effect. That means the electron sees a time varying vector potential which, by: $\vec{E}$ = ...
1
vote
3answers
53 views

Capacitance of a single charged plate?

Lets say we have a single plate that has a charge of +Q on it. A plate with charge -Q is infinite distance away. Will the plate with +Q have a capacitance associated with it? Why or why not? I was ...
1
vote
0answers
109 views

Confused on how to apply the volume integral form of the Biot-Savart law

In Viscous evolution of point vortex equilibria (Jing, 2011) the author explains that the velocity equation for the Lamb-Oseen vortex is found by applying the 2D Biot-Savart law to the vorticity ...
4
votes
1answer
263 views

What creates voltage?

I was trying to break down how a transistor works to a friend, and I took a moment to think about electric current and voltages. I realised I do not understand where these phenomena come from. I ...
0
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1answer
56 views

Calculating the Magnetic Component of a Photon

I've been trying to figure this out for some time. I have found some formulae on other sites that claim to allow me to calculate the magnetic component of a photon, but I have seen so many variants of ...
0
votes
0answers
16 views

Does water absorb microwaves above of beneath its relaxation frequency

I am a bit confused about the concept of relaxation frequency. In my course text we derived a model with the help of Newton's law to describe the movement of polar molecules in an electromagnetic ...
1
vote
1answer
67 views

Would the Lorentz force of the two wires be different?

From the following diagram: Lorentz force can be calculated from the following formula: $F$ = $IL\times B$ What about this wire in the following diagram? Assuming that all the variables are the ...
0
votes
0answers
35 views

Longitudinal Adiabatic Invariant in Magnetic Mirror

I am trying to solve the following problem from Bittencourt's Fundamentals of Plasma Physics (Problem 3.4). I have posted an attempted solution below the problem statement: Consider a system of ...
0
votes
2answers
85 views

What is $c$ in the Lorentz force expression?

The usual Lorentz force expression I am familiar with is this: $$\vec F=q(\vec E+\vec v \times \vec B)$$ I have seen some other versions lately that include an extra factor $1/c$: $$\vec ...
3
votes
2answers
70 views

What are diamagnets and paramagnets?

A paragraph in my text reads: An atom or ion with all electrons paired is not attracted by strong magnets and is termed 'diamagnetic'. In contrast, spins do not cancel when unpaired electrons are ...
0
votes
1answer
74 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
4
votes
2answers
108 views

Is there any other momentum besides the Poynting momentum stored in an electromagnetic field?

I am having some conceptual difficulties with energy and momentum stored in the EM field. The force density at a point is $\rho E + j\times B$ Because of conservation of momentum, and because the ...
0
votes
1answer
52 views

Distance of electromagnetic waves based on frequency

I would like to ask your opinion regarding this matter: Based on the relation of frequency and wavelengths, the higher the frequency, the shorter the wavelengths and therefore the distance of travel ...
6
votes
2answers
684 views

How exactly does a solar flare cause a power line surge?

There are occasional large scale electrical blackouts caused by solar flares. Quebec Solar Flare Blackout My question is: what affects the severity of the problem? It obviously depends on the ...
1
vote
2answers
42 views

Quality Factor in a Parallel LC Circuit

I was wondering if there is a notion of a quality factor in a parallel LC circuit, since there is no resistance. One can show that this circuit has a resonance frequency as follows: Impedance: ...
1
vote
1answer
82 views

Advanced (undergraduate) book on electromagnetism [duplicate]

I am an undergrad student and i have been through a first easy course on electrodynamics and i have used the book of Griffiths which let me satisfied.But the next two courses I will be taking are ...
1
vote
1answer
19 views

understanding shceme field lines - magnetic field

I would like to know if the magnetic field is in "the x-y plane". Does this mean the field lines are actually parallel to the visible line x or y? Or does it mean the field lines are parallel to the ...