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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How to calculate the capacity of an electroscope out of the geometry and why is it independent on the pointer deflection?

How can one calculate the capacity of an elektroscope like the following from the geometry of the setup? How does this formula implies that the capacity does not (approximatly) depend on the ...
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164 views

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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157 views

How does electromotive force (emf) influence electrostatic force in a circuit?

I am learning about emf and I am using university physics of Hugh D. Young which states that when the emf source is not part of a circuit the non-electrostatic force of the source moves charge form ...
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1answer
151 views

Charge distribution on a doughnut shaped conductor

In a spherical solid conductor the charge is always on the outer surface. Even if the sphere has a cavity, the surface of the inner cavity can not carry a charge due to Gauss's Law. What would be ...
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1answer
38 views

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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1answer
145 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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1answer
71 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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355 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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2answers
124 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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2answers
56 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
46 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
30 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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2answers
193 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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1answer
92 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
183 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
59 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
73 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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1answer
52 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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2answers
71 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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1answer
88 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
379 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
34 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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19 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
45 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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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
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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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2answers
122 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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49 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 ...
2
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1answer
111 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
59 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
61 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
55 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
73 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
668 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
104 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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4answers
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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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3answers
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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
57 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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30 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 ...
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1answer
43 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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2answers
148 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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0answers
62 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
125 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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268 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
240 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
61 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 ...
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1answer
176 views

Green function solutions in electrostatics

I have a conducting plate on $x$-$y$ plane. So I have a boundary condition at $z=0$ $\Phi=0$ but, for $z>0$ I have a point charge at z=a which is expected to create a potential. $$ ...