Questions tagged [electrostatics]
Electrostatics is concerned with the electrical fields and scalar potentials of stationary electrical charges and charge distributions. Use this for questions about electromagnetic situations in which currents and magnetic fields are absent, otherwise use the [electromagnetism] and/or [magnetic-fields] tags.
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Why the charge is zero in this problem? [closed]
Say we have a bar centered on the origin, orientated with the z-axis, such that $a$ is the measure of the bar and it has a linear density that varies within $z$ with the following expression $\lambda(...
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Why do charges placed inside a metallic cavity have no effect on outer charges and vice versa?
Why do charges placed inside a metallic cavity have no effect on outer charges and vice versa?
My teacher explained it by electrostatic shielding. He said that the conductor does not allow the ...
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How to correctly use Gauss Law? Why is it used the way it is? [closed]
Gauss Law
$$\oint \vec E . d \vec A = \frac{Q_{enclosed}}{\epsilon _○}$$ From this question, Gauss Law is more fundamental than Coulomb's Law. This seems counter intuitive to me when it comes to ...
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Unique distribution of charge on a conductor
If i place some charge on a conductor then it will distribute itself in such a way that electric field everywhere inside is zero. My text book says that only one kind of such charge distribution is ...
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Why is $\nabla \cdot E = 0$ for outside a charged sphere? [closed]
It seems contradictory to Gauss's Law saying $\nabla \cdot E = \rho /\epsilon$
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Translation of Cabeo's Philosophia magnetica
Is there a translation of Niccolò Cabeo's work Philosophia magnetica into English (or other modern language)? The original text in Latin is available for example here but I can't find any translation (...
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Is the net charge in the interior of a conductor zero even when the total net charge (including the surface charges) is positive?
In the textbook Matter & Interactions by Chabay and Sherwood (chapter 14.6), they say
...any excess charges on a piece of metal, or any conductor, are
always found on an outer or inner surface. ...
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How can we choose a coordinate system to calculate the field strength E [closed]
We have two infinitely long strings charged with a linear charge density λ and -λ, separated by a distance l. The electric potential at a distance r from the center of the strings (r>>l) at an ...
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Capacitance and the battery connection
In the photo I added there is a question and its solution (given). It has been written at last(as I highlighted) that 'in order to get the minimum capacitance, dielectric should be removed and battery ...
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Force on a dielectric medium
Under the influence of an external electric field the dipoles in a dielectric medium arrange themselves. These dipoles will create a field that opposes the external field, resulting in a net field ...
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Electric flux through a square surface by a charge kept above it [closed]
A charge $q$ is placed at shown at a height $a$ above the center of a square surface of side length $a$. I have to find the flux due to $q$ through the surface.
I do not find any symmetric shape about ...
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Derivation of the ring charge from a disk charge with a hole
I am doing a problem in which I am given a uniformly charged disk, charge density $\sigma$, with radius $b$ and a concentric hole of radius $a$ in the $xy$ plane. A part of the problem I would have to ...
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Discharging a capacitor conceptual question
When a capacitor is discharging, why is the potential difference across it at any time $t$ equal to that of the resistor? Do the two potential difference's not have to add up to the EMF of the supply ...
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In the formula of capacitance of a conductor the $V$ is potential of conductor once fully charged or initial potential of conductor used to charge it
capacitance $C=q/V$
The $V$ here is the final potential of the conductor which is to be charged or the initial potential of the source conductor? We are not charging it by using a battery rather ...
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Is the electric field actually perpendicular to the ends of a gaussian cylinder here? [closed]
In this problem from Griffiths', the field at the ends of the cylinder is taken to be only normal to the ends and it is said that "symmetry dictates that E must point radially outwards". Can ...
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Does the charge distribution of two uniformly charged conducting spheres change as we bring them near each other?
Assume that we have positively charged two solid conducting spheres of the same radius and material. It is evident that the surface charge is uniform on them to eliminate the internal electric field ...
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Force on a current carrying conductor in the presence of external magnetic field
I have seen in multiple places that force on a conductor is $I(\mathbf{L}\times\mathbf{B})$ because electrons collide with the conductor and can't leave a conductor. But why can't charge accumulate on ...
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Japan's Maglev Train propulsion and guidance system [closed]
Above image is taken from Japan's Maglev Train youtube video by Lesics at here.
If the electromagnets along the two walls used for guidance of the train (So that it does not hit the walls) is made up ...
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Is there an integral representation of the capacitance matrix?
Suppose we have conductors $\{S_1, S_2,\ldots,S_N\}$ with boundaries $\{\partial S_1, \partial S_2,\ldots,\partial S_N\}$.
These conductors are suspended in vacuum.
Is there an integral over these ...
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Distribution of charge in uniform hollow sphere
In electrostatics we learn that if we put excess charge in a hollow sphere, the charges eventually get distributed on the surface uniformly. But there is one thing I don't understand: hollow sphere ...
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When we say a body is at high potential compared to the other, what can we interpret from this and why flow of electrons takes place? [closed]
When we say electron flow from low potential to high potential when connected, what is the reason behind it. I am bit confused whether it is due to the excess of +ve charge on one body compared to the ...
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Can work be 0 but the potential energy still increase?
Let's say that we have two point charges of same magnitude charge, $+Q$ and $-Q$, separated by distance $d$, and charge +Q is fixed in place. If I move -Q away from the +Q charge by giving it an ...
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Interpretation of divergence of Electric Field in outside a charge
We know that $\nabla •\textbf{E(r)}= ρ(\textbf{r})$.
However, consider a finite volume with volumetric charge embedded in empty space. Since the electric field will decrease with distance from the ...
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Meaning of electric dipole moment
what is the meaning of electric dipole moment?
Or why do we need to define electric dipole moment?
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Tetrahedral Geometry and Potential energy
Intuitively, I'd think it possible to use potential energy to find the bonding angles in methane, but I'm not getting the right answer. Am I missing something?
In a tetrahedral, the faces are ...
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$U=qV$: is my understanding right?
Suppose a point charge (q) moves from point A to point B, only under the influence of an external charge configuration.
ΔU=qΔV: The change of the potential energy of the charge+external configuration ...
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Question on Coulomb force compared to Newton gravity
I have recently started reading Volume 1 of The Feynman Lectures on Physics. I am going through Chapter 2, Section 2-2 Physics before 1920.
I came across this particular discussion within section 2-2:
...
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I can't use $\int \frac{kdq}{\mathcal{r}}$ to calculate the electric potential of an infinite charge distribution, can I?
Since $\int \frac{ kdq }{\mathcal{r}}$ assumes infinity is the reference i can't use it to calculate the electric potential of an infinite charge distribution, right?
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How to choose correct gaussian surface?
Suppose a undisturbed charge of magnitude +q at a certain place in the plane and then consider a point 'p' at a distance r from the charge. To calculate electric field at point 'p' we decide a ...
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Do the molecules inside a dielectric physically move when the dielectric is polarized by an external electric field?
Today a colleague and I had a heated debate over whether, when an external electric field is applied across a dielectric, the molecules in the dielectric actually move/rotate (flip to align with the ...
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Why do negative charges build up at the bottom of a thunder cloud?
I understand that thunder clouds are a congregation of millions of water droplets. As water evaporates from the ground, these water molecules rise up and collide with water molecules of the cloud, ...
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Why do charges outside the closed Gaussian surface not matter for the flux in the event they end inside the surface?
I think I am misunderstanding something elementary. Supposing a scenario where you have a negative charge enclosed in a Gaussian surface, why would the presence of outside charges not affect the flux?
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Why are Coulomb forces on two charges the same?
I wanted to explain to a person knowing some very very basics of physics, why the force of attraction on two charges $Q_1=3nC$ and $Q_2=-1nC$ are the same. Of course my interlocutor thought that $3nC$ ...
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Why is there plasma near the inlet when Voltage is increased to higher Voltage? What can I do to eliminate this?
We built this plasma jet reactor with a side inlet of helium at 2 slm. My question is why is there plasma generated near the inlet where in it should only be at the bottom part. You can check the ...
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Conducting liquid between the parallel plates in a capacitor
Let's consider an electrical circuit consisting of a battery, some resistance and a parallel plate capacitor.
If the space between the two plates of the capacitor is replaced by a conducting fluid (...
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Distant pairs of charges becoming neutral
This is a standard question in EM where you have 2 pairs of charge. When you connect opposite charges with the wires, then we get essentially 2 conductors with net 0 charge. Now thanks to the ...
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Confusion regarding field density
In my query, I'll be discussing a test charge and I'd appreciate any responses
My doubts stem from this statement and might involve misinterpretation of it
"Since the magnitude of B is 10T, ...
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What is the electric field due a charged conducting sheet and a charged conducting plate in terms of $σ$ and $ε°$? [closed]
I am getting it equal to $σ/2ε°$ for a conducting sheet and $σ/ε°$ for a conducting plate. Am I right? If yes then explain it to me why is it so?
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Is Net force per unit charge zero in a conductor in the presence of a magnetic field?
Let's assume there is a perfect conductor. This conductor starts moving with a constant velocity in the presence of an external electric field and magnetic field.
Generally an external magnetic field ...
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Reference point of potential in case of a battery
When we define electric potential of a charge,we need to take a charged body as a reference and then we bring the test charge to calculate the electric potential. Now,electric potential energy is ...
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Does a non-grounded disc, near a charged disc, behave like one side of a parallel plate capacitor?
I’m using a new FEA software and I’m getting an unexpected result.
This is a simplified diagram of my simulation problem. I expect that a disc charged with one volt would have a capacitance similar to ...
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Unexpected generation of plasma far from HV rod electrode. Why is plasma being generated near the encircled part wherein there shouldn't be?
we have built a kHz jet plasma reactor and we are generating plasma at the inlet side every time we increase input voltage to more than 3 kV. Working gas used was argon at 1 slm entering at the side. ...
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Is electric field inside a conductor really always zero?
The standard explanation in textbooks goes that in the presence of electric field (e.g. external electric field) the free electrons inside the conductor will keep moving until electrostatic ...
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Relativistic correction of Coulomb's Law
I am attempting to describe Coulomb's law but with the delay one would get because of the light speed limit. I am aware one could do that using Maxwell's equations because they are relativistic, but ...
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Is the strength of the charge equal on all points on an equipotential surface? [closed]
Since the equipotential is calculated by $V = q\cdot \frac{k}{r}$ I suppose that the charge is the same at any point on an equipotential surface but I'm not sure.
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Why do electric field lines bend towards the normal of a linear homogeneous dielectric sphere?
Why do the field lines of the uniform external field bend towards the normal of the linear homogeneous dielectric sphere as shown in the diagram?
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Why is Coulomb's law still relevant?
There is no scenario where we can use Coulomb's law. There is no static charge. Even if we consider the local charge density to be constant for a system of charges, the individual charges are still ...
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Coulomb field from QED
It is well-known how to obtain Coulomb's law in perturbative QED (e.g. the answers to this question on this site). I am trying to understand if there is any reasonable way to give a meaning, within ...
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Deriving Newton's second law of motion for charged particles [closed]
I am trying to derive Newton's second law of motion for two charged particles with opposing charges and the same mass using Coulomb's law.
Let $q_{(+)}$ and $q_{(-)}$ be positively and negatively ...
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Why aren't "composite" capacitors a thing?
Recently I started researching more about capacitors and I wondered why it's not possible to put a layer with a high electric breakdown strength between two layers of high permittivity? Wouldn't you ...
