# Tagged Questions

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 [tag:electromagnetism] and/or [tag:magnetic-...

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### How does rubbing cause the transfer of electrons from one object to the other? [duplicate]

I have just learnt about electrostatics. Why would there be a transfer of electrons? Is it because of the difference of the materials (i.e. triboelectric series)? So in the case of two different ...
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### Electric Potential Field of Parallel Electrodes within Grounded Shell

Any help would be greatly appreciated I think I need to solve this using boundary potential conditions and Laplace equations. Here is the system I'm attempting to model: The red rods are metal ...
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### What moves the charges between capacitors?

Suppose I charged two capacitors to charges Q1 and Q2. By charging a capacitor to charge +Q , I mean that one plate acquires a net charge +Q and another plate acquires a net charge -Q.The capacitors ...
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### Why aren't +/- test leads connected to battery terminals attracted to each other?

Similar to static electricity, why wouldn't the negative charges accumulate on the wire connected to the negative terminal of a battery be attracted to the positive wire (lead) when their ends are ...
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### Inconsistency with electrostatic energy formulas

The energy of point charge configuration can be written as: $$W = \frac{1}{2}\sum_{i=1}^{n}q_{i}V(r_{i}) \, ,$$ which can take both positive and negative values. However, when we integrate the ...
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### Does the electric force on a charged particle in a uniform electric field increase?

If I have a proton in a uniform field between two parallel oppositely charged plates and the proton accelerates, the electric force acting on it stays constant seeing it is a uniform field and as a ...
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### How to get the electric field strength of a plate as approximation of a sphere

Suppose you know that the electric field in distance $r > R$ from the center of a charged sphere with charge $Q$ and radius $R$ is given by: $$E = \frac{1}{4\pi\epsilon_0} \frac{Q}{r^2}$$ (...
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### Flashing a fluorescent light bulb with high voltage

My son and I built a Wimshurst machine (our second try) over the last couple of weekends. It works -- not terribly well, as it only makes 2cm sparks with 20 cm disks (something like 60 kVolt when it ...
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### Calculating the electrostatic energy per unit length of a cylindrical shell surrounded by a coaxial cable

Suppose an infinitely long cylindrical shell of radius $a$ carries a surface charge density $\sigma_0$ and is surrounded by a coaxial cable of inner radius $b$ and outer radius $c$ with uniform charge ...
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### Electric field in a sphere with a cylindrical hole drilled through it

Suppose that you have a sphere of radius $R$ and uniform charge density $\rho$; a cylindrical hole with radius $a$ ($a\ll R$) is drilled through the center of the sphere, leaving it like a "necklace ...
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### Argument for symmetry of potential

Consider the following electrostatic charge configuration of a spherically symmetric, perfect conductor with total charge $Q = 2q$, where $q > 0$. A point charge $q$ is placed at the position shown....
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### What determines how much electrical charge an object can hold?

What determines how much electrical charge an object can hold? Does increase voltage force more electrical charge to be store in an object (Van de Graaff generator), since electric field increase as ...
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### electrical potential energy stored in vacumm for a single point charge?

I have come to know the electrostatic potential energy in vacuum is given by $${\frac{1}{2}} \epsilon_0\int d^3x {E^2}$$ and this energy is due to the mutual electrostatic coulomb potential energy. ...
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### Conductors and their charge?

Why does excess positive charge stay on the surface of a conductor? This is what I understood from: How does positive charge spread out in conductors? and other resources on the web: If there is a ...
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### In Jackson's expression for the electrostatic Green function, why is the Laplacian taken with respect to the primed coordinates?

Jackson writes, The function $1/|\mathbf{x} - \mathbf{x}'|$ is only one of a class of functions depending on the variables $\mathbf{x}$ and $\mathbf{x}'$, and called Green functions, which satisfy ...
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### Local nature of a surface charge density

Boundary $S$ of a cavity in a very large (perfect) conductor is a connected compact (smooth) surface. A positive point charge $+q$ is placed inside this cavity. From Gauss' law we know that the total ...
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### Coulomb interaction as virtual particles exchange?

I've been reading about virtual particle exchanges in physics books and in Physics SA posts, where a particle interpretation of gravity and Coulomb interaction is established. The Feynman Diagram ...
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### What happens to this potential energy?

Let's say I turn on a Van de Graaff which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters ...
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### Unrolling electrolytic capacitors

If I take an electrolytic capacitor, remove the aluminium casing, unroll the foil/ electrolyte-soaked paper, if charged, will it still work? And what if I took of the cathode foil and wrapped the ...
A problem out of a certain popular book on electricity and magnetism dealt with the resulting electrostatic theory if Coulomb's law was replaced with the following equation: $$\mathbf{F} = \frac{1}{... 1answer 271 views ### Electric arc due to static discharge in a T-Shirt possible? Yesterday, when I came home, I went to the bathroom (lights off) and i took off my T-Shirt (100% cotton) which I wore under a Shirt (50% cotton, 50% polyester). I believe to have seen a small but well ... 1answer 63 views ### Charge in a layered ball A ball (radius R) has three layers. For 0<r<a it is a conductor with free charge +Q. For a<r<b it is a linear dielectric \epsilon with free charge embedded in it with density \... 1answer 1k views ### How much negative charge do I accumulate by touching the earth? The Earth carries a negative electric charge of roughly 500 thousand Coulombs (according to different sources I've seen). If I touch the Earth I should therefore pick up some of this electric charge (... 1answer 6k views ### Force from point charge on perfect dipole Have a point charge and a perfect dipole \vec{p} a distance r away. Angle between \vec{p} and \hat{r} is \theta. Want to find force on dipole. I'm having more than a little difficulty ... 3answers 640 views ### Why does hair stand up when standing under power lines? My initial guess would be the immense electric field around the lines, that causes hair to get charged and due to each hair having the same charge they start to repel each other. So what is exactly ... 3answers 1k views ### How can I find the potential created by spherical capacitor with dielectric material? If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. What kind of a ... 0answers 99 views ### Charge over 2 layer dielectric, image method If I have a charge Q located over a 2 layer dielectric as represented: According to the image method : the charge Q'1 will be located at a distance h_1 under the first interface and the Q'2 ... 1answer 169 views ### Problem from Purcell and Morin's Electricity and Magnetism: Holding the charge in place This is the problem given in Purcell and Morin's electricity and magnetism book. (Problem 3.2 If you have the book) Figure: I was able to figure out that the charges on A,B,C,D cant be held ... 0answers 55 views ### Lightning sprites Lightning usually occurs due to an electrostatic discharge between an electrically-charged cloud and the Earth's surface, or between clouds. There are also sprites, electrical discharges that occur ... 2answers 211 views ### Why in electrostatics is dV=-E.dr but in electromagnetic induction, EMF=+E.dS? In electrostatics we learned that$$dV=-E.dr$$. I understood the derivation which was used to derive this. Now when I have come to Electromagnetic Induction,I see that when there is a time varying ... 1answer 541 views ### Determining potential in coaxial cylinders If I have two conducting, coaxial cylinders as shown: The potential at the outer cylinder is = 0. And I apply a potential difference across both cylinders in the form V_a - V_b = V_{ab}, how can ... 0answers 195 views ### Green's function for a dielectric with a charge [closed] Suppose there are two infinite planes, one in z=a and the other in z=b, with a<b. Between the planes, there is a dielectric medium with constant \epsilon_1. The differential equation for ... 0answers 359 views ### Can spheres leaking charge be assumed to be in equilibrium? I am struggling with the following problem (Irodov 3.3): Two small equally charged spheres, each of mass m, are suspended from the same point by silk threads of length l. The distance between ... 3answers 5k views ### Conductors connected with a wire Let's say I have two spherical conductors with different radii and different amount of positive charge on them. The spheres are far enough from each other. I connect them with a conducting wire. I'm ... 0answers 268 views ### Electron hopping among molecules - Marcus equation I'm running out of professors to talk to, and I need to clarify a couple of things for the sake of making a realistic model of electron travel through a mesh. This is about calculations of electron ... 8answers 3k views ### Why does Coulomb's constant have units? I think of Coulomb's constant as a conversion factor (not sure if this is correct). Kind of like how you would do calculations in kg and then times it by the conversion constant to convert your answer ... 4answers 557 views ### Attractive force between capacitor plates A textbook question requires me to calculate the force of attraction between plates of a parallel-plate capacitor. The answer provided is \frac{1}{2}QE. I am not entirely sure how they arrived at ... 4answers 5k views ### Delta Dirac Charge Density question I have to write an expression for the charge density \rho(\vec{r}) of a point charge q at \vec{r}^{\prime}, ensuring that the volume integral equals q. The only place any charge exists is at ... 3answers 1k views ### Why the electric field \vec{E} is constant (=position independent) for an infinite 2D sheet of constant charge? So I'm reading a text on electricity and it talks about using the integral to compute the total charge of a collection of points, which I mostly understand. But then we get to finding the electric ... 4answers 2k views ### How does instant charging of one plate affect the potential of the other plate of a floating capacitor? If I have an uncharged floating capacitor and I instantaneously connect one plate to some potential, then that plate will acquire some charge. In practice, the other floating plate will ... 3answers 718 views ### How much energy is needed to create an electron? I know how to calculate the electrostatic energy of a sphere (it has a well defined radius). But how can I calculate the electrostatic energy of an electron as it is a point particle? By electrostatic ... 2answers 5k views ### Why electric field inside charged conductor is zero in the electrostatic case? I am trying to understand the idea (or the fact) that most books introduce which is about the electric field inside a charged solid conductor Books tell that the field has to be zero everywhere ... 2answers 1k views ### Does a conductor of total charge zero placed in a uniform external electric field experience net force? The question I have in mind is: If we place a conductor (arbitrary shape) of total charge zero in a uniform external electric field \textbf{E}_0, does it experience any net force? Why (not)? Now I ... 3answers 963 views ### Electrostatic energy integral for point charges The electric energy stored in a system of two point charges Q_1 and Q_2 is simply$$W = \frac{1}{4\pi\epsilon_0}\frac{Q_1Q_2}{a}$$where a is the distance between them. However, the total ... 2answers 445 views ### Shape of electric charges on sphere in equilibrium state When electric charges of equal magnitude and sign are released on a regular sphere (and assume that they stick to the surface of the sphere, but they are free to move along its surface), what is the ... 1answer 357 views ### Need of small charge in definition of electric field? Why do we need infinitesimally small charge in definition of electric field? Since the test charge cannot exert force on itself, F on test charge will not change whatever the value of test charge q is.... 1answer 9k views ### Charge inside conductor I know that the E field inside a conductor is zero. What happens if I put a source of charge inside the conductor? Say the conductor was spherical centered on the origin and there exists a charge ... 5answers 4k views ### The discontinuity of Electric Field ''electric field always undergoes a discontinuity when you cross a surface charge \sigma'' GRIFFITHS In the derivation; Suppose we draw a wafer-thin Gaussian Pillbox, extended just barely over the ... 3answers 131 views ### Why doesn't \vec{E} =\frac{1}{4\pi\epsilon_0} \int\frac{\rho \hat{r}\;dxdydz}{r^2} blow up at r=0, when \rho is finite? Electric field at (x,y,z) produced by a continuous distribution of charges is given by:$$\mathbf{E}(x,y,z) =\dfrac{1}{4\pi\epsilon_0} \int\dfrac{\rho(x',y',z') \mathbf{\hat{r}} \;\mathrm{d}x'\mathrm{...
Imagine this: You have a sphere of air where you have no charge and around this sphere you have a charge distribution $\rho(r,\theta,\phi)$. (For instance, this could be $\rho(r,\theta,\phi)=e^{-r}$)...