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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Electrostatics and two electric charges

How can two identical metallic objects have the same but opposite charges (one loses electrons and one gains electrons) when we know that metals have the ability to lose electrons only?
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Question regarding Van De Graff generator Belt

I have made a VDG generator with a rubber band as the belt and a glass roller. It doesnt seem to work because I think the rubber band may be conductive. I was thinking of using other materials for ...
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52 views

What is the meaning of permittivity of free space?

We all know about the value of permittivity of free space but is this actually enough of for our knowledge? We should be taught that what actually does permittivity of free space means.
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172 views

Numerically solving 2D poisson equation by FFT, proper units

The 2D Poisson equation is: (1)$$\frac{d^2\varphi(x,y)}{dx^2}+\frac{d^2\varphi(x,y)}{dy^2}=-\frac{\varrho(x,y)}{\epsilon_0\epsilon}$$ And in $k$-space it is in form of: (2)$$(k_x^2+k_y^2) ...
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29 views

Does the electric field inside a circuit cause a potential drop with distance?

We know that when the system reaches steady-state(current does not change with time),the electric filed inside the circuit is constant. In many textbooks and lectures,professors make a graph like this ...
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323 views

Effect of charges near a parallel plate capacitor

If I charge a parallel plate capacitor and I insert a charged body near one of the plates will there be any interactions like attraction or repulsion? What if I disconnect the battery?
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1answer
44 views

How to prove using symmetry that electrostatic force acting parallel to the line joining two charges?

The unit vector $\hat{r_{21}}$ shows that the force is parallel to the line joing the charges. It could be otherwise unless space itself has some built-in directional property. . . This can be ...
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2answers
56 views

Flux through plane surface in hemisphere [closed]

Suppose a charge is placed at the centre of a hemispherical surface of radius $R$ then what would be the electric flux passing through the planar surface opposite to the charge in the hemisphere? I ...
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22 views

Continuity of Potential of an electric field

Consider a point charge $q$ at $(0,0,0)$, the potential at $\bf{r}$ is given by $V(\bf{r})$ $= \frac{q}{4\pi\epsilon_0r}$. If you consider a path through $(0,0,0)$, you encounter a discontinuity in ...
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1answer
33 views

Image charges and capacitors?

Consider these two situations: A (infinite) parallel plate capacitor in which one plate is held at a potential $V$ and the other is grounded. A point charge near an infinite plane and grounded ...
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1answer
25 views

Explanation for electrostatic energy expression

My question is about the electrostatic energy $We$ expression for $n$ point charges. I just can't figure out where the factor "$\frac{1}{2}$" came from: $We=\frac{1}{2} \sum_{i=1}^{n} q_iV_i$
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Force between charges when there's a slab of dielectric between them [duplicate]

Consider the following arrangement - Blue and red are two opposite charges +q and -q separated by a distance R. A dielecric slab is placed between them. The thickness of the slab is t. What will ...
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1answer
85 views

Forces between charged particle

I am given two charged particle of same charge at distance of $r$ , they initially apply force of magnitude $F$ now infinite dielectric (of constant 4) of width $\frac{r}{2}$ is introduced between ...
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2answers
162 views

Electrostatic Potential Energy Integral

I'm trying to calculate the total energy of a simple two charge system through the integral for electrostatic energy of a system given in Griffiths' book: $$U = \frac{\epsilon_0}{2}\int_V E^2 dV .$$ ...
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Why the direction of dipole moment is from negative charge to positive charge?

An electric dipole moment is defined as $p = q\times 2d$. How to understand it physically? Why the direction of the electric dipole moment is from negative charge to positive charge?
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1answer
361 views

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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1answer
46 views

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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1answer
132 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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1answer
52 views

Definition of charges

We say that a body is negatively charged when it has excess electrons otherwise say positively or uncharged. We also say that electrons are negatively charged. By the above statement, it has more ...
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4answers
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Why are there dust particles on TV screens?

My professor gave us the following reason: The screen is positively charged. When dust particles fly near it, the positive charges in the screen induce a charge in the dust particle, pulling the ...
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1answer
353 views

Finding Green function using eigenfunction expansion method

Given the Dirichlet boundary condition, I am to show that the functions that satisfy $$(\nabla ^2 + k_{lmn}^2) \psi_{lmn} (x,y,z) = 0$$ are given by $$\psi_{lmn} = (\frac{\pi}{2x})^{1/2} ...
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1answer
19 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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2answers
113 views

Potential generated by a hollow sphere with a hole

The sphere has radius $R$ and is missing its "pole" - meaning that in the area $\theta\leq\alpha$ there is nothing. The object has a homogenous charge density $\sigma=\frac{Q}{\pi R^2}$ I'm trying to ...
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1answer
46 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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46 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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2answers
640 views

How do I express the interaction energy between two charged spheres?

Consider two identical insulating spheres each with radius $R$ and uniform charge $Q$ through their volume. They are separated from their centers by a distance of $d>2R$. Here is my general ...
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1answer
56 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
341 views

Information content of the electrostatic Maxwell equations vs Coulomb's Law vs Poisson's Equation

In electrostatics, we have Maxwell's equations: $\nabla \cdot E = \rho$ $\nabla \times E = 0$ These four equations (the second line standing for three equations) can also be written in terms of the ...
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1answer
24 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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1answer
110 views

Electrostatics problem concerning induction by a point charge inside a conducting shell

Consider two independent conducting shells (not thin shells! i.e., their internal and external surfaces do not overlap.) whose shapes of external surfaces are identical but internal surfaces are not ...
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0answers
17 views

Designing a capacitor and electrical double layer capacitor

Hello! based on the image above, I am wondering if my assumptions are correct that i can make a capacitor using this design (1) and (2) are "infinitely" long layers (1) layer is made up of same ...
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1answer
25 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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0answers
12 views

Electrodynamics of a single ion transport between a dielectric slab

I am trying to solve the mean passage time for a single solvated ion to diffuse through a pore. This pore is surrounded by the medium with a low dielectric permittivity, i.e. around 10. The solvent ...
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4answers
87 views

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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1answer
145 views

How to find the electric field of a charged tube?

Let's say there is a charged tube(cylinder with no top or bottom) with radius $a$, length $l$ and charge $q$ and a point which is collinear with the centre of the charged tube. Anyway, since we can ...
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2answers
52 views

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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0answers
40 views

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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4answers
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Why do grapes in a microwave oven produce plasma?

Some of you may know this experience (Grape + Microwave oven = Plasma video link): take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each ...
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1answer
324 views

Apply Gauss' law to find electric field around nonconducting plastic sheets

The question: Two very large, nonconducting plastic sheets, each 10.0 cm thick, carry uniform charge densities $\sigma_1$,$\sigma_2$,$\sigma_3$ and $\sigma_4$ on their surfaces, as shown in the ...
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1answer
57 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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0answers
39 views

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
32 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
35 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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2answers
4k views

Why does the electric field perpendicular to every point on the surface of a conductor?

I am reading Berkeley Physics Course, Volume 2 (Electricity and Magnetism by Edward M. Purcell). I am in chapter $3$ pg $92$, and the book discusses conductors. The following is from the book: ...
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2answers
61 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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1answer
166 views

Force between two point dipoles

What would the force between two parallel point dipoles be? I was thinking of doing it the way force between two point charges is found out, by finding the field and then the force but I am not able ...
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2answers
46 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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Why does a faraday cage protect you from high currents?

In an electrostatic case it is clear that that in a space enclosed with a conductor (without charge in it) the electric field is zero. This is often demonstrated in physics shows like on the ...
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Why is Energy = Voltage x Charge, and how to prove that?

As you know the equation $\mathbf{E=V\times Q}$. Where: $\mathbf E$ is the energy measured in joules, $\mathbf V$ is potential difference (Voltage), $\mathbf Q$ is the charge. So my qustion is: ...
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1answer
48 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} ...