# 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 ...

935 views

### The maximum distance for which Coulomb's law has been verified?

We know that Coulomb's law, $F_{12} = \frac{kq_1q_2}{r^2}$, was experimentally verified for small distances by Coulomb himself at the and of the XVIII century. The question is what is the maximum ...
39 views

### When two coils carrying opposing currents are placed coaxially

The current flowing through these coils increases in this case according to the book. But it does not clearly state how. This is what it says: "When brought closer induced effects should produce ...
154 views

### Is Coulomb's law valid if the electric charge is not constant in time?

If the electric charge is constant the law of Coulomb says that: $E(r) = kQ/r^2$. The question is, if $Q = Q(t)$, can I consider that: $E(r,t) = kQ(t)/r^2$? Update: It appears that the first ...
54 views

### What does it means to say an electric charged person has a higher potential voltage compared to the door?

I'm studying electric potential energy and its defined as the energy needed to move a charge inside an electric field from a point $a$ to $b$. Then, it defines electric potential energy per charge, ...
178 views

### How electrical energy is transfered trhough a wire, and what's flow of charge?

I've read these texts about misconceptions about electricity. This is my understanding: Electrons do move, mut slowly and randomly. What happens is that, in fact, they're just 'conducting' the ...
33 views

### Does chemical formula of matter influence on how would it be charged? [closed]

Suppose we rub glass ($\mathrm{SiO_{2}}$) against paper(which is made from cellulose ($\mathrm{C_6H_{10}O{5})n}$). We receive positively charged glass and negatively charged paper. Is that because of ...
28 views

### Uncharged metal rod brought near a charged electroscope. Why does divergence of the leaves decrease?

Could someone please explain the redistribution of charges (if any) in a charged conductor that is being used to induce charge on another conductor?
49 views

### Thought experiment and faraday cage

this is my first and second questions. I'll start with my assumptions and go from there to ask my questions. Please do not hesitate to correct me if any of these assumptions are wrong. Inside of a ...
49 views

### The force applied by two charges on each other when there is another charge nearby them

QUESTION 1 Let me give two simple scene of charged particles to make you understand my question. There is a fixed positive charged particle in the center. Scenerio 1 : A fixed negative charged ...
54 views

### Does an observer measure magnetic field when moving inside a static E field?

Imagine a static electric field shaped as a sinusoid created by an array of electrodes on an infinite line. Does an observer flying parallel inside this e-field measure an h-field ?
31 views

### derivation of the electic displacement D

I've been revising Maxwell equations recently and tried to prove that the electric displacement $\mathrm{\nabla \cdot D = 0}$ in the electrostatic approximation ($\mathrm{E = - \nabla} f$). My steps ...
39 views

### Where does the net charge on a hemisphere appear to act from?

I was wondering if, like centre of mass, there is anything called "centre of charge".
309 views

### Electric Potential, Work Done by Electric Field & External Force

I did lot of searching but couldn't find any textbook nor any webpage which could clarify my doubt. Maybe my doubt is insanely stupid and I was dumb for not realizing it at the first place. The ...
75 views

### dielectric polarization

Suppose a small solid sphere made of an isotropic dielectric is introduced in the field of some given system of remote charges. Assuming that the polarization in the dielectric does not affect the ...
52 views

### How much electric charge can a copper sphere, made of N atoms, contain?

If somebody wants to charge a cooper sphere made of N atoms, what is the maximum positive charge the sphere can reach? Same question about a negative charge. Source For example if the sphere is ...
78 views

### Simple model that explain the flow of electrons in metals

I am not quite clear about how electrons (negative electric charges in general) flow through a metal. I imagine the metal as a lattice of small positive charges $+q$ that can not move and the - and + ...
52 views

### How to estimate function from PDF and covariance? [closed]

I've added a picture of what I want to compute. In the nomenclature of the picture, I want to compute a realization of y(x) given the known distributions and constants. Let's say y(x), random ...
76 views

### Divergence-free vector field on a non-simply connected domain

We know that divergence-free vector fields are themselves curls of vector fields on simply connected domains. I want to construct a counterexample in the case the domain is not simply connected. So ...
49 views

### Why can we replace a cavity inside a sphere by a negative density?

I have a sphere with radius $R$ and inside this sphere there is a smaller sphere with radius $\frac{R}{3}$. This small cavity has its center at $\frac{R}{2}$, it doesn't matter in which direction. If ...
37 views

### Integration path with opposite direction from the unit vector

The task is to calculate the voltage between points $M$ and $N$ if the electric field vector is known to be $\vec{E}=\frac{V_0\cdot x^2}{a^3} \cdot \vec{i} + \frac{V_0 \cdot y}{a^2} \cdot \vec{j}$, ...
86 views

### Electric field and electric scalar potential of two perpendicular wires

So, I've been trying to come up with an idea that seems plausible to me for the last half week or so, but I'm stuck and I can't seem to get anywhere with this problem. The problem is as follows ...
48 views

### Two points in a charged hollow sphere with zero potential difference

Two concentric spheres (I've provided a simple sketch below) with radii $a$ and $b$ are given. The space between two spheres (colored yellow) is charged homogeneously, meaning that the charge density ...
68 views

### Is Gauss electric flux law valid in all coordinate systems?

The derivation of Gauss electric flux is as follows : $$\iint{\vec{E}}\cdot{\vec{dS}}=\iint E \, dS \cos\theta \, .$$ The projection of infinitesimal area on the surface $\vec{dS}$ on the radial ...
475 views

### Why are potential differences equal across two capacitors in parallel, but charge on each capacitor is not?

Two or more capacitors are said to be connected in parallel if each one of them is connected across the same two points. In a parallel combination of capacitors potential difference across each ...
20 views

### How to understand Steady Currents within the limits of Magnetostatics

I know that the precise mathematical statement of local charge conservation is $\nabla \cdot \vec{J}=-\frac{\partial \rho}{\partial t}$, where $\vec{J}$ is the volume current density and $\rho$ is the ...
30 views

### Electric Field from a distribution of charge

We have a thin flexible rod bearing charge $Q$ of length $L$. This is bent into a semicircle. Find an equation for the electric field in terms of $Q$, $L$, and appropriate constants at the point ...
51 views

### Image charge distribution for an infinite non conducting plane

If I have a charge +q at a distance d above an infinite non conducting plane, why should the image charge at d below the non conducting plane be +q?
28 views

### Dipole moment of a displaced charge distribution [duplicate]

This one is part b) of the problem I asked a day ago. Special thanks to MarkMitchison and sbp on the first part. I finally got it. (How can I prove that the dipole moment is zero?). Alright, back to ...
64 views

### Spherical Conductors in Dielectric - Potential

I have computed the electric field of the following system between the two spheres, but my calculations for the potential do not make sense. The potential should be proportional to $\frac{1}{r}$ but I ...
105 views

### Can the surface charge density be negative somewhere on the inner surface of a spherical conductor shell?

A positive charge $q$ is located off-centre inside a conducting spherical shell. We know that the total charge on the inner surface of the shell is $-q$. Is the surface charge density negative over ...
92 views

### Battery and charge separation

In this question : What is the difference between a battery and a charged capacitor? http://physics.stackexchange.com/q/32394 It is said that the battery does not have a charge separation on its ...
24 views

### Explanation to the flow of charge

I came across a really cool Cymatics video: There is one part in the video which is unclear to me. Please refer to the snapshot below taken at 05:15. I see the equipment being close to a Van de ...
151 views

### Calculating effective capacitance of a circuit [duplicate]

Please refer to the image below. The question asks: 'The effective capacitance between terminals A and B in the network shown in the adjoining figure is?' Here is my working: (C5 and C6 connected ...
109 views

### Radially symmetric charge distribution (dipole moment) [closed]

a) There's a radially symmetric charge density $\rho(r)$ centered around the origin. Determine the dipolemoment of that charge density. b) Let $\rho(r)$ be an arbitrary charge density now. ...
91 views

### Charges on capacitor after full charge by battery

When the charging is finished what will be the charge on an ideal parallel plate capacitor ? To be specific what are the charges on different faces of the 2 plates ? All the books say, after 100% ...
81 views

### Potential vs Potential Difference for a line charge

How would I calculate potential for an infinite line of charge a distance 'r' away from it? What does the reference point for potential difference mean? I know delta v = Q/(2pi*epsilon0*L)*ln(r2/r1) ...
66 views

### Parallel Connection of Capacitor

Assume Two Capacitor filled with different dielectrics with dielectric constant $K_1$ and $K_2$ respectively in Parallel connection. Then we have same voltage $V$ on both capacitors. Therefore, ...
51 views

### Transfer of electrons and static electricity

From what I currently understand about static electricity, electrons "jump" from one object to another, which object loses electrons depends on where it falls on the Triboelectric series. For example ...
23 views

### Physical Invariance and Method of Images

I will motivate my question, then state explicitly. If I have a system with one point charge and a grounded plane as here, then I can solve for the potential by solving a similar system with two ...
76 views

### Are the boundary conditions for a sphere in an electric field affected by its charge?

Find the potential outside a charged metal sphere (charge $Q$, radius $R$) placed in an otherwise uniform electric field $E$ I know this question can be solved by the method that so called ...
60 views

### Work done by Electric Field vs work done by outside force

I'm confused as to the signage of the equation: W=qv, W=-U, W=-qv? When is work positive? When is it negative? Why is this different for the work done by the electric field vs the work done by an ...
48 views

### Field inside an infinite uniform rectangular box, diverges?

I was solving by direct integration the problem of an infinite rectangular box, with a nonzero width, e; charged with a constant density, $\rho$, as shown in the following picture: The integrals ...
2k views

### Is it (practically) possible for a large building to be a Faraday cage?

In my sophomore year of high school, my P.E. teachers kept on complaining about how phones didn't have a network connection in our gym, regardless of model, service provider, etc. A couple of feet ...
25 views

### Electric field of a charged conductor

It’s been said that the electric field of a conductor is always perpendicular to its surface. However, I’m having difficulty understanding this. There are only a limited number of excess charges on ...
19 views

### How Maxwell's equations are derived from fundamental equations for electrostatic and magnetostatic models [duplicate]

How Maxwell's equations are derived from fundamental equations for electrostatic and magnetostatic models.
15 views

### General electrostatics in dieletric

I was told that the electrostatic potential inside a dielectric is the sum of the solution of the Poisson Equation for the boundary condition V=0 for |t-t'|->Infinity plus a solution of the Laplace ...
331 views

### Method of Images - Line Charge Above Infinite Grounded Plane [closed]

For a uniform line charge, $\lambda$ placed on an infinite straight wire at a distance $d$ above a grounded conducting plane. We let the plane run parallel to the x-axis, and directly above it ...
68 views

### How big of a capacitor would I need to release 5 amps for 0.2 seconds? [closed]

Just what the title says, 5 amps for 0.2 seconds. Please bear in mind that I have absolutely no grasp on electrical wiring, so I would appreciate simple terms. What I need to do is release a burst of ...