# Tag Info

### 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 ...
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### 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 ...
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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, ...
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### 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 ...

### Densities at a Point

You are on the right track. Matter and charge are often treated as continuous. It is a good approximation. Air exerts a pressure on the walls. You think of it as a continuous fluid. In reality, the ...
• 41.1k
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### 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 ...
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### Densities at a Point

It is a matter of approximation. Yes charges would not normally be concentrated into a point, but the specifics of charge distribution will normally contribute to second and third order effects. For ...
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### 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 ...
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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.
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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. ...
• 41.1k
1 vote
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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
1 vote
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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 1 vote ### 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 1 vote ### 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})&... • 6,686 1 vote ### 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 1 vote ### 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 ... • 73.6k 1 vote ### Why is the electric potential from a positive sphere not negative? You have a really wonderful doubt. You did the calculations right, except for the dot product. It is a error easy to overlook.(Note: bold means vectors). Dot product E.dr is equal to Edrcos\theta\$. ...
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