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Questions tagged [electrostatics]

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 [tag:magnetic-fields]

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2answers
18 views

Why are there 6 interactions with 4 positive charges?

From a homework assignment, there are 4 spheres spaced 1cm apart. Each of the spheres are charged to +10nC and weigh 1 gram. The question wants us to find the final speed of the charges once they've ...
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1answer
23 views

Voltage between parallel capacitor plates

We know that $C=q/U$. We know that the voltage is the potential difference between the plates. If we have a capacitor on which we apply voltage, the one plate charges up and induces the other one with ...
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0answers
25 views

What is the energy associated with the degrees of freedom of a nucleus?

I am following Martin in his book on electronic structure. On page 11 he explains that we discriminate between properties of matter due to the electric ground state, and excited states. He writes ...
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1answer
31 views

Gauss' Law not including all of the system

Suppose we have a system of two parallel conducting plates charges $Q$ and $-Q$ and charge densities $\sigma$ and $-\sigma$. In this case, to find the electric field, Gauss' Law is used with a ...
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1answer
17 views

Why are Cauchy boundary conditions an over-specification of boundary conditions for solving Poisson’s equation?

I was referred to Physics.SE by the following content published in Jackson’s Classical Electrodynamics: This rather surprising result [the fact that the potential within a charge-free volume is ...
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1answer
18 views

How to disturb a particle distribution

I have a set of N macroscopic particles, each representing a group of electrons. Each of these macroscopic particles has a different charge. My system is one-dimensional so all particle´s positions ...
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1answer
29 views

Doubt in understanding the potential energy of dipole in external electric field?

When a dipole is placed in external electric field it experiences a torque $$\vec \tau = \vec p \ \times \vec E $$ whose magnitude is $$||\vec \tau|| = ||\vec p|| \cdot ||\vec E|| \cdot sin\theta$$ ...
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1answer
29 views

How can I prove Poisson's equation from direct substitution

I’ve got this question where I should take the Laplacian of electric potentials main formula, then it should hold the Poisson’s equation. I’ve somehow gotten close to doing this but I just can’t get ...
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1answer
24 views

What makes rheoscopic particles align?

In a rheoscopic fluid, it is said that particles (mica traditionally) align with neighboring ones so that patterns can be seen. What forces are responsible for the alignment ?
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1answer
40 views

Why do the sides of the Gaussian pillbox contribute nothing to the electric field? [on hold]

It says that the top and bottom of the pillbox contribute to the $E$ field but the sides don’t. I couldn’t quite understand this, please Help.
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1answer
28 views

Why is electric field constant over the charged solid Gaussian sphere?

I saw this example at griffiths. It’s a basic question about gauss’s law but I saw the electric field being treated as a constant and thus, it got outside of the integral. I couldn’t quite understand ...
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1answer
35 views

How does one include the magnetic scalar potential in the electromagnetic four-potential?

The electromagnetic four-potential is typically written as $$A_{\mu}=(\phi,\vec{A}),$$ where $\vec{A}$ is the magnetic vector potential, and $\phi$ is the electric scalar potential. Should I want to ...
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0answers
17 views

What are some good model quantum systems in external electric fields?

I want to understand a few things on the behavior of atoms and molecules in (weak, non-ionizing) external electric fields. For this, I am looking for model systems that might have an easily ...
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0answers
15 views

Ions vs charged plate

In an ammonium chloride solution, if I put in a positively charged plate, do ions still remain entangled with water or do they get ripped apart and stick to the charged plate?
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0answers
31 views

What is the function $q$ in the definition of charge density?

Supposed we define $\lambda = \frac{dq}{dl}$. If I think of this intuitively, this makes sense; the linear charge density at a point is tiny amount of charge at that point divided by the tiny length ...
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0answers
9 views

Electric potential of a charged spherical conductor using laplace equation

Reviewing a course of electromagnetism I encountered the problem of a spherical conductor with a charge of $Q$ in a uniform electric field. The problem of a conductor in a uniform electric field (a ...
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1answer
21 views

Point with 0 electric field and non-zero potential

I'm quite new to physics and I don't totally understand the concepts of potential energy and work. I've been watching MIT courses and I got pretty confused, considering the following situation: We ...
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1answer
22 views

What is the space that lack a charge density?

In the section 1.7 Poisson and Laplace equations in the book of classical electrodynamics 3rd ed. for J. D. Jackson, it has been mentioned, that in regions of space that lack a charge density, the ...
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1answer
64 views

Does $T= qV$ hold true for relativistic case?

In relativistic case, kinetic energy $T\ne 1/2mv^2$, m is mass and v is speed. But if a particle( initially at rest) of charge q is accelerated through a potential difference $V$ the kinetic energy ...
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1answer
37 views

Electric potential due to two spheres

The setup is as below: The two conducting spheres, of radii $r_1$ and $r_2$ have charges $Q_1$ and $Q_2$. The distance between their centers is AB. BC is perpendicular to AB. The problem asks to ...
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0answers
19 views

Qualitative definition for potentials

I am doing an E&M course and just started with the concept of electric potential, potential difference, etc. I know how to work with them mathematically, but I don't have an intuition for their ...
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0answers
21 views

Vector components for the dipole of water

I was looking online for the components for the dipole moment vector of water in the molecular frame. Does anyone know what the values would be for $\mu_x$, $\mu_y$ and $\mu_z$ for a water molecule in ...
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1answer
17 views

Energy of the system of similar charges

We know that two same charges repel each other. To stop the charges from going away we have to exert an external force and hence energy is used. But if in a vacuum two similar charges are placed near ...
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0answers
51 views

Why is this equation correct?

This problem seems to be solved the exact same way in multiple solution books, so I'm certain that the way it is done is correct and that I'm just rusty when it comes to calculus due to multiple years ...
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0answers
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Retarded Coulomb's law and EM waves; Feynman texts

In this chapter, Feynman writes down the retarded Coulomb's law, $$\begin{equation} \label{Eq:II:21:1} \mathbf E=\frac{q}{4\pi\epsilon_0}\biggl[ \frac{\mathbf e_{r'}}{r'^2}+\frac{r'}{c}\,\frac{d}{dt}\...
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1answer
30 views

How to calculate this electric field? [closed]

I can't solve this question. Please help. Q: Solve using Multiple integrals (Gauss is not allowed). A hemisphere of radius $R$ has a uniform distributed surface charge density $ρ_s$. Calculate ...
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1answer
21 views

Electric power correction

The electrical energy is defined as: $$ E(t) = Q(t)V(t)$$ The general definition of power: $$P(t)=\frac{dE(t)}{dt}$$ and becomes $$P(t) = \frac{dQ(t)}{dt}V(t) + \frac{dV(t)}{dt}Q(t) = I(t)V(t) + \...
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4answers
49 views

The potential at a point

According to my book, 'The potential at a point is said to be 1 volt when 1 joule of work is done in bringing 1 coulomb charge from infinity to that point.' But I wonder how it is possible. As the ...
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1answer
16 views

What distance do I use when examining the effect of an electric field on a point outside of a nonconducting sphere with an arbitrary volume charge?

It's easy enough for me to do this for a ring (as I interpret the field lines as "exiting from the centre of the ring") or a point (simply the distance from the point to the other point), but I just ...
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1answer
40 views

Nature of induced magnetic field lines in cylindrical capacitor

What is nature of the induced magnetic field lines inside a cylindrical capacitor which has a time variant potential gradient across it? For a parallel plate capacitor, its straightforward: the ...
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1answer
14 views

The electric field inside a conductor and Gauss' law

The electric field inside a conductor must be zero. Can this be explained with the help of Gauss's law? Also, how does this explain that if we have a conducting sphere with a cavity inside, and we ...
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1answer
36 views

Difference of potential between 2 disks of radius $R$ where $d << R$

Well, We have 2 disks of radius R where the distance between these 2 disks : $d << R$. These disks are uniformly charged. I have calculated the electric field near one disk, I have: $$E(z) = \...
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0answers
23 views

Is it (practically) possible to create non-uniform electrostatic in the form of a Fourier series?

Is it (practically) possible to create a non-uniform electrostatic field of the form $$E_x = \sum_{k=0}^N C_k e^{ikx}.$$ (keeping it in one dimension for simplicity) If yes, how?
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0answers
47 views

Directly integrate $\mathbf{E}$ inside a spherical cavity in dielectric [closed]

P3-23 in Cheng E&M, 2nd edition: Determine the electric field intensity at the center of a small spherical cavity cur out of a large block of dielectric in which a polarization $\mathbf{P}$ ...
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0answers
9 views

How to measure how much charge can be stored in an object using a multimeter?

Certain powders (ex. mixture of aluminum and carbon powders) can store quite substantial amounts of electrons. I'd like to ask for an advice on how to correctly measure the capacitance of such a ...
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0answers
28 views

Finding the potential off axis of a uniformly charged disk

This is problem 3.22 from Griffiths We know the potential at any point on the axis perpendicular to the center of the disk, I'm asked to find the potential at any point $(r,\theta)$ assuming $r<R$ ...
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1answer
38 views

Why electric potential energy at a point is the same as amount of work done to bring the charge to that point from infinity?

Let's consider a positive charge at a point in the space. Now, if we want to bring a another positive charge to a point within the electric field of the first charge, then we have to do some work ...
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0answers
76 views

Poisson equation in Jackson's textbook

I use a relatively new version of Jackson's electrodynamics textbook and I already saw that this part of the chapter is not in older versions. Jackson wants to show us that the Poisson equation $\...
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1answer
13 views

What is the reference potential when considering electric potential on a body in case of self capacitance?

I was taking a lecture on self capacitance and the word 'potential of the conductor' came up. Now, self capacitance is for isolated conductors. From what reference is this potential measured?
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11 views

What is the nature of the multipoles used to shape/re-direct an e-beam?

Imagine having an electron beam, just like in an electron microscope. Now imagine that we have some multipoles prepared in the beams path to influence the shape/path of the beam. My question is: ...
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3answers
43 views

If voltage represents an energy difference between two points, why don't electronic appliances all use the same amount of energy?

As I understand it, voltage is an energy difference between two points. $$V_f - V_i = - \int \mathbf{E} \cdot d\mathbf{s}$$ But consider a toaster and a refrigerator each using their own 120V ...
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1answer
25 views

Two point charges $Q_1$ and $Q_2$, are a distance a away from each other. Where is electric field zero? [closed]

Problem: Two different point charges $Q_1$ and $Q_2$ are a distance $a$ away from each other. The point charges are both positive. Where is the electric field zero? So far, I've found the total ...
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0answers
24 views

Gauss law in electrostatics

Consider a solid conductor,if the conductor makes a free electron inside that due to thermal energy ,so that causes one positive ion inside the conductor, my question is according to gauss law inside ...
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1answer
40 views

What would be tension developed in a conducting ring of radius $R$ which has been given a charge $Q $, uniformly in the ring? [closed]

As the question says , i thought about using coulumbs law , but for any small dq charge , all other part will be attracting it , so.how to get the total tension force ( difficulty is in as distance ...
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1answer
33 views

What exactly is an anode/cathode?

Whenever I look for answers I find stuff about batteries and chemical reactions. But in videos like these about thermionic emission there suddenly is a positively charged anode ring which pulls the ...
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1answer
28 views

How would a electrostatic lens accelerate a continuous beam of electrons?

Truthfully, I am somewhat confused by this topic. Electro-magnetic lenses are created by coils, through which one runs a current, which then in turn generates a magnetic field whose field lines are ...
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2answers
47 views

Charging a metal by friction

Why is it so difficult to charge a metal by friction, even if the metal is insulated? (For example, rubbing a fork hold by my hand wearing a plastic glove?) If I wear a glove, electrons can't pass ...
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2answers
97 views

In electrostatics, $\nabla\times\mathbf E=0$. Why is this?

I can understand why this is mathematically but I do not understand the actual why, like in words why this is.
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3answers
49 views

$E$ outside a Metal Spherric Shell with a off-center Point Charge inside Shell

If a charge +Q is placed inside a metal shell (NOT at the center), as shown below. I can understand that E will be 0 between inner surface and outer surface due to this is a conductor. Then according ...
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0answers
22 views

Difference between electrostatic lens and electromagnetic lens

Imagine an electron-beam in a scanning electron microscope. From what I've gathered usually electro static fields are used to accelerate the electrons to a desired speed. At the same time electro-...