All Questions
Tagged with electromagnetism capacitance
241
questions
2
votes
1
answer
29
views
Energy in Dielectric Medium as a Sea of Dipoles
Simply, why is the energy density in a dielectric medium = $\frac{1}{2}K\epsilon_oE^2$ where K is the dielectric constant of the dielectric medium?
Working proof
Consider a capacitor that is charged ...
- 35
0
votes
2
answers
49
views
Maxwell stress tensor on a capacitor late given a dielectric
Given a capacitor with large plates (area $A$) separated by a dielectric with relative permittivity $\varepsilon_r$ and thickness $g$, I believe the Maxwell stress tensor states that the force on each ...
0
votes
2
answers
57
views
Growth of Current in an Inductor Connected Across a Battery [duplicate]
When baterry is connected across inductor with no resistance in circuit, won't the current flowing through it be zero, as inductor back emf will counteract the effect of potential difference due to ...
0
votes
2
answers
73
views
Cannot catch a minus sign mistake when deriving the ODE for an LC circuit
It's probably a very basic question but I just cannot wrap my mind around it. I'll just try to derive the differential equation for an LC circuit:
According to the law of induction, in a solenoid we ...
- 4,887
0
votes
2
answers
34
views
For a plane isolated capacitor with a dielectric slab partially introduced inside it, what's indpendent of the medium? $\mathbf E$ or $\mathbf D$?
Say we have an isolated capacitor with charge $Q$ and a dielectric slab, $\varepsilon_r$, partially introduced between the capacitor's plates, then, I'd say the displacement vector should be the same ...
- 296
2
votes
0
answers
23
views
Capacitance coefficients of two enclosed spheres
I was reviewing G.B. Jeffery's work titled On a Form of the Solution of Laplace's Equation Suitable for Problems Relating to Two Spheres. To access the full text, you need to click "DOWNLOAD PDF&...
0
votes
2
answers
68
views
Maximum Impedance for LCR series circuit
Impedance of an LCR series circuit can be maximum when either Inductive Reactance or Capacitive Reactance is maximum at an instant of time.
Max Capacitive Reactance is at minimum frequency, and max ...
0
votes
1
answer
53
views
Why doesn't current flow stop in LC oscillation?
Why doesn't current flow stop in a LC circuit? It is supposed to stop when the magnitude of emf developed across capacitor is the same as the inductor, right?
2
votes
1
answer
45
views
How does the presence of a static electric field affect the normal operation of an antenna (if at all)?
For arguments sake lets say I have a receiving antenna that has been positioned between two large conductive plates. Are there any differences in how that antenna operates (gain, efficiency etc.) when ...
- 113
1
vote
2
answers
78
views
Telegraphers' equations for lossy transmission line when $R$, $L$, $G$, and $C$ are frequency dependent
The telegraphers' equations are commonly written as
$$\frac{{\partial v(z,t)}}{{\partial z}} + R\space i(z,t) + L\frac{{\partial i(z,t)}}{{\partial t}} = 0$$
$$\frac{{\partial i(z,t)}}{{\partial z}} + ...
- 11
1
vote
2
answers
77
views
How does capacitance of a capacitor not depend on the distance of the capacitor to a battery?
When you consider the positive terminal of battery, wire and capacitor plate, they form a single conductor, which is polarised by the field of the other capacitor plate, but it is not polarised as ...
- 155
2
votes
1
answer
67
views
Does parasitic capacitance contribute to the magnetic flux?
When modeling a real inductor, typically the equivalent circuit is the following one:
Source
A series resistance and parallel capacitor is added.
This model works very well to explain the following ...
- 187
0
votes
0
answers
61
views
Total capacitance from a capacitance matrix
I am currently doing a project where I need to find the capacitance of a multi-conductor system. Through my literature review, I read about the concept of a capacitance matrix. After more research, I ...
0
votes
1
answer
34
views
How to find the capacitance between two metal sheets [closed]
Let’s say I have two metal sheets in a 2D plane. The first one has area A, the second one is infinitely long, and they are separated from each other by a distance d. How can I find the capacitance ...
0
votes
1
answer
83
views
What is the electric potential difference for two spheres capacitors connected in series [closed]
Consider two spherical capacitors with Identical radii for the inner and outer spheres (let them be a and b). +q and -q charges are in the inner and outer sphere on Both the capacitors. Now I connect ...
- 123
2
votes
5
answers
109
views
Magnetic field in a capacitor in a $LC$ circuit
Consider a simple $LC$ circuit in which the charge on the capacitor varies sinusoidally. Current flows in this circuit, changing the charge on the capacitor and hence changing the electric field ...
- 29
1
vote
1
answer
780
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Trying to understand how to apply Maxwell stress tensor to calculate forces
I'm struggling to understand how to use Maxwell's stress tensor to compute electromagnetic forces acting on surfaces. I'll take problem 8.7 from Griffths Introduction to Electrodynamics as an example.
...
- 171
3
votes
1
answer
342
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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
29
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Corona Discharge, Leyden Jar and Free Charge [closed]
Watching Walter Lewin's 8.02x- Lect 14, at the end of it, he explains the mechanism behind a Leyden jar. The (simplified) picture is the following:
Source: https://www.youtube.com/watch?v=By2ogrSwgVo
...
- 115
2
votes
0
answers
42
views
What if two plates charged with different charges are placed face to face?
I'm asking this question because I can't solve it even if I ask a lot of smart people. (Please understand that I don't speak smoothly because I use a translator. I'm korean student..)
In the next ...
- 21
0
votes
1
answer
77
views
Capacitance matrix is diagonally dominant
I have heard of the following claim “the capacitance matrix of an isolated system of conductors is diagonally dominant” but I couldn’t find a way of proving it myself or any reference for that matter. ...
- 402
1
vote
2
answers
358
views
Relation between resistance, capacitance and resistivity
I recently learnt that for a resistive medium, $RC = ρε$ where $R$ is the medium's resistance, $C$ is the capacitance, and $\rho$ is the resistivity. Now, I am able to prove that this is true in the ...
- 301
1
vote
1
answer
29
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Charging capacitor moving with respect to the dielectric
Suppose I am charging a capacitor, so that a magnetic field is generated. This capacitor is placed inside a dielectric material with permittivity $\epsilon$ and then it is moved parallel to it's ...
- 49
1
vote
0
answers
105
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Capacitance of a System of Two Spheres
To explain more clearly, I am looking for how one would derive an expression for the capacitance of a system which consists of two conducting spheres of radius $a$ separated by a distance $d>2a$. I ...
- 11
4
votes
5
answers
2k
views
Can you charge a capacitor with only voltage (without current)? If No, then how does a capacitor correct power factor?
Let me explain you why I am asking this question.
The other day I was studying about power factor correction of a (step up or any) transformer. It said that on the output side of transformer's ...
- 129
0
votes
0
answers
83
views
How do you determine the electromotive force when the negative plate of the capacitor is connected to the positive terminal?
$\newcommand{\d}{\mathrm{d}}$We have a square wave source with period $T$ and voltage $V_0$ connected to a circuit which is has a resistor of resistance $R$ in series with an uncharged capacitor of ...
- 221
0
votes
1
answer
51
views
Enhanced capacitance by magnetism?
Consider the first picture.
This is much like a parallel plate capacitor charged by a battery. But instead of parallel plates we are using parallel rings. The rings are attracting each other because ...
1
vote
0
answers
40
views
Why do two infinite planes contribute to Electric Field but not two surfaces in co-axial cylinder
I understand why the electric field between two infinite planes is $\frac{\sigma}{\epsilon_0}{\vec{e_z}}$. Both planes contribute to the field - the upper positive charged plane "pushes" ...
- 149
1
vote
1
answer
151
views
Does a spherical capacitor hold as much energy as a spherical shell?
Consider a spherical capacitor, that is, two concentrical spherical shells which serve as plates. Suppose the capacitor is charged. It is my understanding that the energy stored by a capacitor is ...
3
votes
0
answers
194
views
Wave equation derivation in a transmission line
$$
V(x, t) = L\Delta x\frac{\partial I}{\partial t}(x, t) + \frac{1}{C \Delta x}\int{I_c(x, t) \; dt} \tag{1}
$$
$$
V(x + \Delta x, t) =\frac{1}{C \Delta x} \int {I_c(x, t) \; dt} \tag{2}
$$
$$
I(x) = ...
- 1,525