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 ...

learn more… | top users | synonyms

1
vote
1answer
75 views

What happens to the energy of a capacitor after a dielectric is inserted?

Consider a parallel plate capacitor having capacitance $ C$ and charge $Q$. then the energy of the capacitor will be $\frac{Q^2}{2C}$. Now if a dielectric is inserted, then $C $ increases and thus the ...
1
vote
2answers
66 views

Curl of Electrostatic Field

In Griffith's EM text he calculates the curl for the E field of a point charge (at the origin). He shows that the line integral of an arbitrary closed loop is zero: $$ \oint E\cdot dl = 0 $$ and ...
2
votes
1answer
142 views

Dielectric slab inserted into a constant voltage capacitor

I was told that a dielectric slab inserted into a capacitor connected to a battery (constant voltage) will be repelled, because the energy stored in the capacitor increases when the dielectric is ...
2
votes
2answers
76 views

Directly calculate electric potential due to a spherical volume charge

Q: Say we have a uniformly charged sphere with radius $R$, total charge $Q$. Now we need to find out the electric potential inside the sphere, at a distance r from the centre. I understand that we ...
0
votes
2answers
114 views

Wouldn't $D = \epsilon E$ mean that a higher permittivity constant gives a higher electric flux? (And what exactly is the displacement field?)

A quote from the Wikipedia page for Permittivity: More electric flux exists in a medium with a low permittivity (per unit charge) because of polarization effects. This makes sense to me. My ...
1
vote
1answer
58 views

How two electric charges know about each other? [duplicate]

Suppose we have two electric charges $q_1$ and $q_2$ a distance $r$ apart in euclidean three-space. Coulomb's force law states that there's a force $$\mathbf{F}_{12} = \dfrac{1}{4\pi\epsilon_0} ...
0
votes
0answers
32 views

Capacitor of Pearson–Anson oscillator

I was calculating capacitance of Pearson–Anson oscillator and comparing with simple RC circuit but I get two different values. They have significant difference. I am not clear why do they have. Could ...
3
votes
1answer
46 views

Potential energies of charges and spring

I wonder if someone could sanity check this very simple calculation. Consider a pair of charges $+q$ at rest separated by a spring of length $d$ and stiffness $k$. The spring provides the force that ...
0
votes
0answers
69 views

Dipole moment of a specific charge distribution

A negative charge cloud distribute as a ellipsoid and a positive point charge situated at the centre of the ellipsoid.What should be the dipole moment of charge distribution.I mean, if the negative ...
0
votes
2answers
159 views

Electric field 0 everywhere inside Gaussian surface

Gauss's Law shows that the electric field everywhere inside a spherical shell of uniform charge density is $0$. Suppose we have a surface which divides space into two disjoint regions (an interior and ...
0
votes
2answers
281 views

Confused about Gauss's Law for parallel plates

I am having trouble understanding Gauss's Law. Suppose we wish to find the electric field strength between two parallel plates with charge density $\sigma$. I know it should be ...
1
vote
2answers
275 views

Coulomb's law and Gauss' Law

Which of these laws is more fundamental or forms the basis of electrostatics? I started off with Coulomb's law and then I studied Gauss' law. I was wondering which one is more universal? My professor ...
0
votes
2answers
66 views

Calculating the electric field of an infinite flat 2D sheet of charge

I was trying to calculate the electric field of an infinite flat sheet of charge. I considered the sheet to be the plane $z=0$ and the position where the electric field is calculated to be ...
1
vote
2answers
136 views

Using a charged capacitor to charge two others [closed]

Here is the homework question in question: The figure (below) displays a 13.1 V battery and three uncharged capacitors of capacitances C1 = 4.08 μF,C2 = 6.19 μF and C3 = 3.30 μF. The switch is thrown ...
0
votes
1answer
56 views

potential inside a cylindrical shell in terms of the surface potential?

Given a potential distribution $V(\phi)$ at the surface of an infinite cylindrical shell, is there an easy way to derive the potential inside the cylinder. No charges or currents anywhere.
0
votes
2answers
68 views

Paradox in electrostatics in relation to Gaussian surfaces?

I have encountered something that is very confusing. My problem is this. I am assuming two infinite cubical Gaussian surfaces sharing a common side. One of the cubes contains a charge $q_1$ at a ...
0
votes
2answers
44 views

How can I use volume charge density to find charge density constant knowing charge Q

I have an insulating sphere of radius R that has a total charge Q. It is distributed as $\rho$= $\rho_0*r^4$. I know that the charge is equal to Q and I'm trying to solve for $\rho_0$. I've tried to ...
0
votes
1answer
58 views

Electromagnetism and static electricity

What is the difference between electromagnetism and static electricity? Also electromagnetic waves are mediated by photons , what mediates static electricity?
0
votes
0answers
69 views

Potential due to infinite plate carrying a finite charge

I've solved many problems where something is grounded and you've to figure out the charge distribution. The general strategy is to set the potential of the grounded thing equal to zero and solve. ...
0
votes
0answers
43 views

What are some open problems in classical electrodynamics? [duplicate]

I am about to finish reading 'Introduction to Electrodynamics' by David Griffiths. Throughout the textbook, Griffiths makes frequent references to current literature (mostly articles from American ...
0
votes
0answers
22 views

Defining the region in Laplace's equation

1) Consider a sphere S centered at the origin O, where a charge q is present. Is Laplace's equation applicable in the region S? No, right? 2)This is where I go crazy.... Instead of considering the ...
0
votes
0answers
28 views

How can a potential step be modelled?

a potential step is given by function $V(x) = V_o, x\geq 0$ and $V(x) = 0, x\leq 0$ Using the relation $- \frac{dV}{dx} = \vec E$ I take the negative derivative of this function, i'll get ...
0
votes
0answers
44 views

Does voltage depends on the charge present in an element?

Does the voltage depend on the charge present in a battery ? I know in capacitors q=cv. Hence charge present is proportional to voltage. Is it the same in the case of batteries?
0
votes
1answer
37 views

What's the Relation between Potential of mechanics and electricity?

As we know that for a conservative force field, there is associated a Potential with the force. But we know there is a potential in electricity (That's voltage). My question is that is there any ...
1
vote
1answer
29 views

Accelerating an electron to a high speed

Suppose there are two vertical metal plates. They are separated apart by a small distance. While one is grounded, the other one has a potential of some $V$. Now suppose electrons are produced at the ...
0
votes
0answers
34 views

Anyone know of a flow chart or list of common/useful consequences of Maxwell's equations?

I just recently started to appreciate the Maxwell equations. I had never really take the time to study them but I feel like I'm finally more familiar with them. I've noticed that it seems like a lot ...
1
vote
1answer
119 views

Electric Flux - What is the point?

Electric flux is a defined quantity that is proportional to the no. of field lines passing through a given area element for a given electric field. It is not proportional to the relative density of ...
0
votes
1answer
220 views

Electric field and charge density outside two coaxial cylinders

I am working on a problem of electrostatics, and I am having troubles in trying to figure out one part of it. It consists of an inner solid cylinder of radius $a$ with a voltage $V_A$, and an outer ...
0
votes
0answers
37 views

Why are trampolines more likely to give you a static shock when it is sunny?

It could just be in my head but I have noticed that I am more likely to get a static shock from my tramp when it is sunny than when it is not sunny. Is there a reason for this?
-1
votes
1answer
18 views

Plastic and Iron - static and magnetic

I'm wondering if when you have a ball that is made out of plastic but has an inner core of metal. Would that ball if given friction produce static? Or would the static from the outerside of the ...
1
vote
1answer
126 views

Wait… why exactly does farady's ice pail experiment prove Gauss's law?

You'll notice there are no equations in this: that's because this is a question of morale, not of math. But a humble one at that! I come to learn, not to expound. But don't let that limit the form ...
0
votes
0answers
162 views

Electric Flux through cube from point charge

"A point charge is located at the origin. Calculate the flux of E through a cube centered on the origin and aligned with the Cartesian axes. Evaluate the surface integral directly and verify that the ...
0
votes
2answers
254 views

Why does excess of charge in an isolated conductor move to the surface?

A remark in my textbook goes as follows: "If an excess charge is placed on an isolated conductor, that amount of charge will move entirely to the surface of the conductor. None of the excess charge ...
0
votes
2answers
54 views

Is work needed to bring a test charge from a higher potential to a lower potential?

I don't understand whether work is needed to bring a test charge from a higher potential to a lower potential. It seems that no work is needed because the positive test charge will be under the ...
0
votes
0answers
115 views

Finding potential of conducting sphere coated by a dielectric shell

An uncharged conducting sphere of radius $a$ is coated with a thick insulating shell (dielectric constant $\epsilon_r$ out to radius $b$. This object is now placed in an otherwise uniform electric ...
0
votes
1answer
86 views

Calculating flux of axisymmetric electric field through a sphere [closed]

The following problem and its solution is taken from I. E. Irodov's book basic laws of electromagnetism : I do not understand how the fact that field is axisymmetric leads to the conclusion that ...
2
votes
0answers
47 views

What is the essential concept behind the difference in the fundamental solutions of the Stokes and Poisson equations?

The fundamental solutions, i.e., the solution with a point source, of the Poisson's equation and the Stokes equations in 3D are: $$\nabla^2 f=\delta(\boldsymbol x) \ \Longrightarrow\ G(\boldsymbol ...
1
vote
0answers
37 views

Can a charge moving in an open trajectory qualify as current?

It is sometimes said that a point charge is equivalent to an electric current. If it were a steady current, I should be able to find it from Ampere’s law or Biot-Savart’s law. Even if the current is ...
1
vote
1answer
315 views

Rigorous proof of Gauss' law for an arbitrary charge distribution from Coulomb's law

Most of the books about electromagnetism prove Gauss' law for a point charge in vacuum: $$ \Phi = \int_{\Sigma} \mathbf{E} \centerdot d \mathbf{S} = q/\epsilon_0 $$ and then simply state that for ...
0
votes
2answers
81 views

Relativity Paradox involving two charged particles

Suppose there are two charged particles separated by some distance $d$ both with an equal positive charge of $q$. The particles also have equal masses of $m$. $m$ and $q$ are chosen so the ...
1
vote
0answers
16 views

Energy density in electrostatics

Imagine two hollow spheres with radius $R$ with charges $q$ and $-q$. $L>2R$ is distance between them. Potential energy of the each sphere is \begin{equation*} W_1=\frac 1{8\pi \epsilon_0}\frac ...
0
votes
1answer
44 views

Divergence of a vector field, going through the math [closed]

The example I'm working on has this given identity: $\bigtriangledown \cdot \mathbf{\bar{r}}=3$. The question is: find the divergence of a vector field $\bar{\mathbf{E}}=\frac{\mathbf{r}}{r^{3}}$. ...
0
votes
0answers
48 views

Why does charge build up at the boundary surface of two media?

On a homework problem, we are asked to to use the first two Maxwell equations, $$\nabla\cdot \mathbf{B} = 0$$ $$\nabla \cdot \mathbf{D} = \rho$$ to show that along the boundary surface of two ...
0
votes
1answer
70 views

Energy density what volume?

In a derivation of energy density for an electric field (see here) We get rid of the $$\epsilon_0\oint(V \vec E \cdot d\vec a)$$ term by choosing a surface sufficiently far away so that this term ...
0
votes
0answers
44 views

Motion of charge particle under electric and gravitational fields

I am working on one experiment in which the charged particle falls under the effect of gravity and passes through the electric field in between. I want to know what is the charge of the particle? ...
0
votes
2answers
39 views

Is it inevitable to compute the quadruople tensor in components? Why? [closed]

I was trying to determine the quadrupole tensor for a given charge distribution in one go from this equation: $$\overleftrightarrow{D}=\int d^3r \varrho(\vec{r})\left(3\vec{r} \circ ...
0
votes
1answer
36 views

Electrostatic induction in spheres

if we have a charged sphere with charge Q and radius r, the voltage on it's surface is calculated by gauss's law, what if we approach to it another sphere with radius R , R>r, earth it, remove earth, ...
0
votes
1answer
40 views

How to determine electric field strength without Gauss's Law

For objects which do not subscribe to Gauss's Law, I don't understand how one would determine the electric field strength. I know that the equation $E=k\int \frac{\mathrm{d}q}{r^2}$ can be used to ...
0
votes
1answer
77 views

What is the charge density in the proof of Earnshaw's theorem?

I am trying to understand the proof for Earnshaw's theorem. Though the theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration ...
1
vote
2answers
77 views

Electrostatics Basic Question

Why ,if we increase the charge on a conductor its potential also increases? That is, Q directly proportional to V. Why ,if an insulated conductor is given some charge it acquires a certain ...