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 ...

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Why may an air passenger experience an electric shock when he touches the door knob of the toilet of an aeroplane flying at a high altitude?

Why may an air passenger experience an electric shock when he touches the door knob of the toilet of an aeroplane flying at a high altitude?
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328 views

Gauss Law for a Modified Coulomb's Law

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} = ...
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361 views

Energy Loss during Sharing of Charge between two Capacitors

It is fairly easy to show that there is always a loss energy when two capacitors share their charge to attain the same common potential, but is it with the same ease that one can explain why it ...
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483 views

Why is there lightning where there are no clouds?

Recently my family and I went onto the balcony to observed the stars in the night sky. We started to see flashes in the sky and we realized that it was lightning (non fork lightning). I looked around ...
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70 views

Electric field of a full disk - when $R \to 0$ - it's not equal to coulomb law

An MIT document states that the electric field of a full disk, when $R \to 0$, is similar to Coulomb's law $$\mathbf E_{disk}=2\pi ...
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1answer
199 views

Question on boundary condition for Maxwell's Equations and Coulomb's law

When deriving Coulomb's law using the differential forms of Maxwell's equation, the boundary condition that $\phi = 0 $ at infinity is also used. From $\nabla × E = 0, E = \nabla \phi$ for some ...
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1answer
118 views

Poisson equation in non-homogenous media

If the dielectric constant be different in x, y, and z directions, how the Poisson equation would change. Is it right to say: $$ \epsilon_{xx} d^2V/dx^2 + \epsilon_{yy} d^2V/dy^2 + \epsilon_{zz} ...
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Induced charge in a mobius strip

I know that when a positive charge is placed at the center of a circular ring, the "inside" of the ring will have a negative induced charge and the "outside" will have a positive induced charge. ...
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1answer
483 views

How do electrostatic air filters really work?

Supposedly electronic air filters work by ionizing dust (small airborne particles) and then attracting them to filter plates of the opposite charge. What I don't understand is why the filter plates ...
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Approximations of the kind $x \ll y$ [closed]

I have an expression for a force due to charged particle given as $$F=\frac{kQq}{2L}\left(\frac{1}{\sqrt{R^2+(H+L)^2}}-\frac{1}{\sqrt{R^2+(H-L)^2}}\right) \tag{1}$$ where $R$, $L$ and $H$ are distance ...
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What would be the charge distribution in a Klein bottle?

We know that for any conductor the charge lies on the outer surface at electrostatic equilibrium. What would happen if a Klein bottle is made up of a conductor and a charge is placed on it?
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Electric field of infinite slab

When reading a book about basic electrodynamics (in a section about electrostatics), I came upon the following problem: An infinite plane slab, of thickness $2d$, carries a uniform volume charge ...
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Elementary electromagnetism problem - Electric field generated by points that form an equilateral triangle

I am a newbie at physics and i just started learning electromagnetism at the university. Some help would be very welcome on the following questions (my question and/or result and/or partial work will ...
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1answer
343 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 ...
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2answers
2k 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 ...
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1answer
662 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 ...
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3answers
201 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 ...
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2answers
516 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 ...
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1answer
87 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} ...
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59 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 ...
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147 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 ...
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2answers
311 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 ...
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366 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 ...
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2answers
665 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 ...
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2answers
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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 ...
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2answers
357 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 ...
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1answer
192 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.
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2answers
87 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 ...
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2answers
93 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 ...
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1answer
189 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?
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104 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. ...
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0answers
48 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 ...
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0answers
115 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?
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63 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 ...
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1answer
30 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 ...
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48 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 ...
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3answers
740 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 ...
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1answer
752 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 ...
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1answer
29 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 ...
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1answer
313 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 ...
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0answers
341 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 ...
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2answers
928 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 ...
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2answers
89 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 ...
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1answer
114 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 ...
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0answers
71 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 ...
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1answer
58 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 ...
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1answer
521 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 ...
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109 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 ...
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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 ...
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1answer
67 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 $\bar{\mathbf{E}}=\frac{\mathbf{r}}{r^{3}}$. ...