4
votes
Accepted
Charge conservation in ohmic material - Apparent paradox
Differential problems are defined in a domain and require boundary conditions, and the solution to be "regular enough" for the differential equations to hold.
If you're dealing with a body ...
- 10.7k
4
votes
Dipoles as vectors
Rotational dynamics. The governing equation of the rotational dynamics of a system w.r.t. to its center of mass reads
$$\frac{d \boldsymbol{\Gamma}_G}{dt} = \mathbf{M}_G^{ext} \ .$$
Considering only ...
- 10.7k
3
votes
Accepted
Does cutting out the surfaces with no surface charge affect the charge distribution on the remaining parts of a conducting surface of arbitrary shape?
Removing the uncharged parts of a charge distribution would not change the field configuration elsewhere. To show this, start with the Poisson equation (assuming the permittivity $\epsilon_0$ is the ...
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Why don't positively charged metal ions (in a wire) move but electrons do?
The question is why the ions are localised and form a lattice, unlike the electrons. The reason is that they are typically 10000-100000 times heavier than electrons. Therefore they have very small, ...
- 25.3k
2
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Accepted
Why don't positively charged metal ions (in a wire) move but electrons do?
To answer this question, it is necessary to understand
the structure of the metal at the atomic scale. A very simple way to see it is that the positively charged nuclei sit at fixed points in a ...
- 1,897
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Why don't positively charged metal ions (in a wire) move but electrons do?
It’s because the ions aren’t delocalized like the electrons are.
- 29
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Does the geometric shape of the cross-section of an infinitesimally thin conducting charged thread (wire) affect its electric field?
I assume the charge is uniformly distributed around the major radius for all these tori.
You are right. Shape and conductivity make smaller and smaller differences as a torus approaches a thin ring.
...
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2
votes
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Do conductors have bound charges?
You are correct. In a typical conductor, like a metal, the charges are all considered free charges. That includes both the mobile electrons and the immobile lattice protons.
The reason is, as you say, ...
- 103k
2
votes
Accepted
Understand power rating in layman terms
You stated that when one coulomb of charge passes through the bulb then $220\,\rm J$ of electrical energy is converted into heat and light.
This is a correct statement but you must now realise that it ...
- 97.9k
1
vote
Do conductors have bound charges?
The language at the outset is different from what is used in a chemistry of materials perspective. It also leaves a sense of sloppiness, throwing around terminologies and using somewhat circular ...
- 2,899
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Do conductors have bound charges?
In a metal the free charges counter external macroscopic fields. Therefore there is no polarisation of the bound, inner, electrons. For ultraviolet frequencies and beyond this is no longer true and ...
- 25.3k
1
vote
Accepted
Electric field experienced by a charge
What we measure (with a load cell for example) is the force on charge 2. And we can test that $F \propto \frac{Q_1Q_2}{r^2}$.
Then we define the electric field in the location where $Q_2$ are as: $E = ...
- 16.7k
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Electric field at a point due to dielectric inserted in between a parallel plate capacitor
The induced charges on the dielectric will attract the charges on the plates. Since the dielectric is inserted partially between the two plates, the charge on the plate near the dielectric will ...
- 513
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Electric field at a point due to dielectric inserted in between a parallel plate capacitor
Consider the situation before the dielectric was introduced (left diagram) and after the dielectric was introduced (right diagram).
There are two possible scenarios.
The first is when the capacitor ...
- 97.9k
1
vote
Accepted
Flux change through a loop
This comes from Faraday's law. I believe it is only valid in quasistatic (no radiation generated) situations.
Faraday's law in differential form is
$$-\frac{d\Phi_B}{dt} = \varepsilon.$$
If you have a ...
- 978
1
vote
Accepted
Electrostatic potential outside of a charged ball
Starting from the general form of the electrostatic equations $$\begin{align}\mathbf{\nabla} \times\mathbf{E}(\mathbf{r})&=0 \tag{1} \label{1}, \\[5pt] \mathbf{\nabla} \cdot\mathbf{E}(\mathbf{r})&...
- 6,734
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Voltage: work to move a charge, or difference of electric potential?
In the diagram below the red dashed circle with the negative charge at its centre is an equipotential with the electric field lines produced by the negative charge at right angles to the circle.
As ...
- 97.9k
1
vote
Accepted
Voltage: work to move a charge, or difference of electric potential?
it will take work to move the positive charge from point A to point B, as I must counteract the vertical component of the electric force and so on.
You are quite correct that the distance to the ...
- 358k
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Charge besides conductor
The positive charge produces an electric field which if nothing happened on the adjacent conductor would pass through the conductor.
However the induced charges on the conductor also produce an ...
- 97.9k
1
vote
Accepted
What is charge on a fundamental level and what is it caused by?
Electric charge is a fundamental physical property of matter, like mass is a fundamental physical property of matter. Fundamental may be defined as "affecting or relating to the essential nature ...
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