All Questions
Tagged with maxwell-equations electric-current
58 questions
0
votes
0
answers
122
views
Is Ohm's law incompatible with Maxwell's equations and the continuity equation?
Every electromagnetic system should be uniquely determined by Maxwell's laws and the continuity equation, so in order to use Ohm's equation $\vec{J}=\sigma \vec{E}$ should I remove one Maxwell ...
- 95
0
votes
0
answers
31
views
Eddy current and thickness of tube
Suppose we have a bar magnet and we are dropping it through different metal tubes which have different thicknesses. If we assume that all the different tubes have same length, conductivity and inner ...
0
votes
0
answers
44
views
Why aren't there in vacuum any charges nor currents?
In this video (MIT $8.02$ course titled "Electricity and Magnetism", video number $214$, taught by Pr. Krishna Rajagopal), professor considers Maxwell's equations in the special case of the ...
- 754
0
votes
1
answer
61
views
Ampere-Maxwell Equation & Non-Continuous Current
The Ampere-Maxwell equation suggests that current causes a circulating magnetic field, but there seems to be an assumption that current is continuous.
Current can obviously be modeled as continuous in ...
- 15
0
votes
1
answer
126
views
Why doesn't putting a magnet in a coil create a current?
According to Amperes law the integral of the magnetic field $B$ dotted with the $dl$ along a closed loop is proportional to the current passing through the surface area of any shape given by the ...
- 3
0
votes
1
answer
77
views
Infinite/recursive solution for magnetic field due to a long straight wire?
I'm trying to use Maxwell-Ampere's law to find the field due to a long straight wire, but I keep running into some circular reasoning...
Maxwell-Ampere's law states that $\oint_c \vec{B} \cdot \vec{dl}...
- 307
0
votes
1
answer
49
views
Integrating current density for cylindrical symmetry
Considering a constant current density, $\vec{J}=\frac{I}{A}\hat{k}$, and also assuming there is no displacement current in the situation, how would one apply Maxwell-Ampere's law? I keep running into ...
- 307
2
votes
2
answers
282
views
Confusion with displacement current
I'm currently studying maxwell's equations in class, and my professor has explained the concept of displacement currents. The idea makes sense to me -- I mean, after all, isn't that entirely how a ...
- 307
3
votes
1
answer
407
views
Doubt regarding a possible mistake in Griffiths Electrodynamics
Griffiths, in section 7.3 Maxwell's Equations, says:
There’s another way to see that Ampère’s law is bound to fail for nonsteady
currents. Suppose we’re in the process of charging up a capacitor (Fig....
- 702
1
vote
1
answer
128
views
Doubt regarding microscopic averaging of current density
We know that when averaging the velocity vector field of a current distribution over a particular volume, we get velocity fields that are slow varying over macroscopically small / infinitesimal ...
- 702
0
votes
0
answers
73
views
Voltage and current spacetime propagation in a circuit
It is often stated that for lumped circuits the signal propagation can be considered instantaneous, so the the circuit parameters do not depend on space coordinates.
But how to actually derive this ...
- 543
0
votes
1
answer
36
views
Find the strongest point of the magnetic field from three long conducting wires
Consider three long power lines buried in the ocean, with (from left to right) current $\frac{I}{2}, I, \frac{I}{2}$, where the direction of the current in the edge cables are negative $z$ (in to the ...
1
vote
2
answers
1k
views
How does the continuity equation mean that the charge is conserved in the neighbourhood of any point?
I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th Edition, by Max Born and Emil Wolf. In section 1.1.1 ...
- 939
0
votes
2
answers
945
views
How to determine if a given charge and current density function satisfy continuity equation?
$$\nabla \cdot J = -\partial\rho/\partial t$$
is the continuity equation for charge.
Meaning that any charge density and current density function I input into Maxwell's equation, must fit this ...
- 6,946
0
votes
1
answer
131
views
Current Density in conductor in DC Mode
I was trying to calculate the current density in a conductor subject to DC voltage but I come to an absurdity. I took a circular copper conductor.
Situation scheme
I have considered the Drude Model : $...
