Questions tagged [charge]

A fundamental property of matter which causes it to experience electromagnetic forces.

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2answers
171 views

How to find the electrostatic potential of a hydrogen-like charge density?

I've been trying to find the scalar potential that would correspond to the charge density of a ground state hydrogen atom. The result is known, and the inverse of my problem can be found e.g. in ...
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1answer
37 views

Reconstructing Charge Distribution from Multipole Expansion

Let $\rho$ be a static, discrete or continuous charge distribution, and $\phi(\mathbf{r})$ the corresponding electric potential. We may expand $\phi$ in a multipole series, $$ \phi(\mathbf{r}) = \frac{...
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0answers
32 views

Conserved charges generate transformations

Focussing on classical mechanics of a point particle, WLOG since it captures the relevant information for field theory and generalises to the quantum case, how do we show -- in general -- that ...
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1answer
46 views

Do photons influence charged particles? [duplicate]

As a neutrally charged particle, a photon shouldn't interact electrically with another charged particle. However, since photons are electromagnetic waves, they should interact with charged particles, ...
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1answer
90 views

Why is a Coulomb the charge of $6.24 \times 10^{18}$ electrons? [duplicate]

Where does the $6.24 \times 10^{18}$ number come from? How was it historically derived? I know that $1$ C $=$ $1$ A s but that just pushes the question down another step, and another and another, at ...
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2answers
59 views

Is it correct to say that electro-static potential of a charge is the energy of a motionless charge?

Is it correct to say that electro-static potential of a charge is the energy of a motionless charge? I ask this to better understand this (great) answer;
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1answer
49 views

Can total charge be transferred from a conductor to another isolated conductor?

Suppose a conductor is charged (Total charge $Q$). Is there any method by which we can transfer the whole charge Q from the initial conductor to another uncharged isolated conductor? What another ...
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5answers
116 views

To store 1 Coulomb of charge [closed]

One teacher told me that to store 1Coulomb charge we need a material of about 7 times of Earth. And another teacher told me that what he said was wrong. who is correct?
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1answer
69 views

Differences charge quantity and electric charge

First of all,my english is not well,so sorry for reading. As a senior middle school from China mainland,I am teaching physics about electri field.I with my workmates,get a problem now.We can not get a ...
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1answer
18 views

What is the physics interpretation of work done of zero when moving a charged particle on an equipotential surface?

Assume I have a test charge of + 1 coulomb. If I move the test charge from a point with potential of +9 volt to another point with potential of -1 volt then the work done by me is -10 joule. This ...
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1answer
52 views

Force on a Charge

I apologize, as this question is quite basic. Suppose we have a point mass of mass $m$. Suppose it is at position $r(t)$ at time $t$. Then the magnitude of the force on this mass is $\ddot r(t) m$ ...
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21 views

Do charged conductors exhibit an equipotential surface even when subject to an $E$-field?

A charged conductor, in the absence of an electric field, attains an electrostatic equilibrium such that its surface has a constant potential. When a neutral conductor is placed in a uniform electric ...
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2answers
92 views

Field of a uniformly charged disk: integration question

In my book (University Physics by Young and Freedman), during solving the common example of finding the electric field along the x-axis from a uniformly charged disk, they arrive at this differential ...
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2answers
55 views

Why bending or reorienting the wire does not change the validity of Kirchhoff's junction rule?

Kirchhoff’s junction rule is based on conservation of charge and the outgoing currents add up and are equal to incoming current at a junction. but Bending or reorienting the wire does not change the ...
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1answer
104 views

From volume density to surface density

Let us say we have a volume $V$ having a volumetric mass(charge) density $\rho(x,y,z)$. Suppose we have a smooth surface $S$ within the volume with a surface mass(charge) density $\sigma(x,y,z)$, if ...
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0answers
45 views

Intuitive explanation why electrons move from low to high electric potential

I know almost nothing about physics but am about to learn some electronics. I have trouble understanding why electrons move from low to high electric potential based on the definition given on the ...
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1answer
47 views

Charged conductor in an external electric field

If we put a conductor in a place where there is a uniform electric field, then the field will change. Take for example the case of a conducting cylinder, then the field lines would curve to return ...
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2answers
73 views

On proving that charge is linearly proportional to potential for a conductor

In Mr. Purcell's Electricity and Magnetism, page 103, it is stated, An isolated conductor carrying a charge $Q$ has a certain potential $\phi _{0}$, with zero potential at infinity. $Q$ is ...
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3answers
135 views

What happens to the charge density under parity?

A question came to me when I tried to think about the parity prperties of the Maxwell's equations. The charge density $\rho(\vec{r})$ actually stands for a scalar quantity $\rho(x,y,z)$. Since the ...
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2answers
195 views

From Poisson's equation to Laplace's equation [closed]

I want to understand how exactly $$ \nabla^2 V = - \frac{\rho}{\epsilon_0}$$ turns into $$ \nabla^2 V = 0.$$ Of course it is by setting $ \rho$ equal to $0$ but what does setting $ \rho$ equal to $0$ ...
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1answer
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What binds electrons to a negatively charged material?

This is probably a very stupid question but I couldn't find an answer on google. Consider a neutral material - say, some block of metal. There is exactly as many electrons as protons and the ...
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1answer
19 views

Is there a concise way to find where on an axis the net electrostatic force will be zero?

Given 2 charged points with charges $q_1$ and $q_2$, where $q_1$ is at the origin and $q_2$ is $d_2$ to the right of $q_1$, I am supposed to find an algebraic expression for where a third charge $q_3$ ...
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113 views

Electric field Between Sphere and Plate

I have a homework question and it goes a bit like this. A solid spherical conductor of radius R is placed at a height d directly above the centre of a square conducting plate of area A. The sphere ...
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0answers
37 views

Strange material, Bydrogen

Let's take a hypothetical scenario in which you manage to make a meta material in which the bulk of the mass is made of by a central negative nucleus and that has a single spin 1 boson whizzing around ...
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1answer
48 views

Does the electric field of a charged particle really contribute to its mass? [duplicate]

An electron at rest creates a static distribution of an electric field around it. Wherever the particle moves, it carries or drags the field with itself. Does this electric field contribute to the ...
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1answer
27 views

How does change in magnitude of a point charge reflect change in its electric field at a particular point in space with respect to time?

We know that electric charge of an object results in an electric field formed around it. We also know that varying the magnitude of a point charge does not instantly produce a change in the electric ...
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1answer
63 views

Tangential component of electrostatic field on a charged surface? [duplicate]

This is a question from class 12 Physics NCERT Part I: Show that the tangential component of electrostatic field is continuous from one side of a charged surface to another. [Hint: Use the fact ...
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1answer
59 views

What exactly happens when a charged conductor comes into contact with an electric insulator?

Let us say we have a negatively charged conducting sphere: If we put an insulator into contact with the sphere: Would the negative charges located in the contact region transfer from the surface of ...
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1answer
53 views

Why is the electric field of a conducting sheet of charge double the electric field of just a sheet of charge?

I was reading Feynman's Lecture on the Application of Gauss' Law and I came across this: Source This really confused me. What are the "other" charges he talks about? How does the additional field ...
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3answers
122 views

Why don't capacitors hold charges on the outer walls of the plates? [closed]

Suppose I have two metal plates in a vacuum and I give this system some electric charge,the charge would distribute itself according to Gauss law on both the inner and outer walls of both plates...but ...
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1answer
38 views

How does induction work when a body is charged (ie) not neutral?

I know that for a neutral body, if a point charge is placed next to it, induction works something like this: Consider a uniformly charged conducting body with charge Q on it. We place a positive ...
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3answers
394 views

What happens when electrons reach the battery?

We have a capacitor which is connected to a voltage source. The top plate of the capacitor is connected to the positive terminal of the source. Therefore, electrons go from the top plate to the ...
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2answers
36 views

Regarding charge densities and the amount of charge located on a point for continuous charge distributions

Suppose we have a volume $V$ containing a charge distribution defined by $\rho (\textbf{x})$. The amount of charge $q~(P)$ located at an arbitrary point $P(x_{0},y_{0},z_{0})$ is : $$q(P)=\int_{x_{0}...
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1answer
34 views

How can we find the charge distribution of $n$ external electrons on the surface of a conducting cube? [closed]

Suppose we take 'n' electrons and put them on the surface of a conducting cube. How can we calculate the charge distrubution and position of these electrons once the static situation has been arrived ...
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1answer
30 views

Inconsistency regarding two charge elements on a uniformly charged disk

Let us say we have the following uniformly and positively charged thin disk: Suppose also that the total charge on the disk equas $Q$, with which we could define a constant charge density $\sigma$ ...
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1answer
57 views

Coulomb's law and the continuous charge model in an infinite charged plane [duplicate]

The $E$-field of an infinite plane with a uniform charge density $\sigma$ has a constant magnitude equaling $2\pi\sigma$. Now, this magnitude assumes a continuous charge model throughout the plane. ...
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1answer
52 views

Work done by charged particles [closed]

A proton is kept at rest. A positively charged particle is released from rest at a distance d in its field. Consider two experiments; one in which the charged particle is also a proton and in another, ...
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1answer
43 views

Is there an easy way to tell whether this “Curlmeter” would rotate or not?

Let us say we have the following symmetrical apparatus: Four equal positive charges, all connected to a shaft that can rotate, the connecting rods are insulated, and so does the shaft. Now ...
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2answers
69 views

Null electric field at infinity? How? [closed]

Suppose there are two charges (4uC each) fixed in the horizontal axis. One is in x=0 and the other in x=8m. I've obtained the electric field: $E=-k\cdot4\mu C \cdot [\frac{1}{x^2}+\frac{1}{(x-8m)^2}]...
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1answer
62 views

Infinite parallel plates have the same electric field between no matter the distance?

I saw this in a lecture about gausses law in application to infinite charged planes: How is it possible that the electric field above the top plane and below the bottom plane is always zero, given ...
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4answers
2k views

Is charge point-like or a smear?

Coulomb gave the law for the force between two static charges while considering them to be points in space. But the differential form of Gauss' Law talks about charge densities, a thing possible only ...
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2answers
51 views

Confusion when applying Gauss's Law to a charged sphere

We have a charged sphere with charge Q and the charge is uniformly distributed with a charge density ρ. The sphere has a radius R. If we construct a Gaussian Surface with radius r, with r < R. If ...
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1answer
25 views

Electrical energy of a charge distribution and the work required to assemble it

The electrical energy of a charge distribution is equal to the integral of $\,E^{2}dv/8\pi$ over all space, and if I have a charge distribution of finite extent, then the energy is finite. Moreover, $...
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1answer
56 views

Path independence of the line integral of the electrostatic field created by an arbitrary charge distribution

Suppose we have the following situation: A positive arbitrarily shaped charge distribution. The line integral of the total electric field, generated by the whole distribution, from $A$ to $B$ is ...
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2answers
65 views

What is actually being removed when a metal conductor is grounded?

I found this image earlier this morning, and yes, there are a lot of diagrams/illustrations about this, transferring charges by induction has been introduced since the very beginning of high school ...
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1answer
38 views

Why did the experimenter touch the circular plate in this demonstration?

In this introductory physics experiment demonstration, the experimenter went through the following procedure: First, he charged the rectangular plate by rubbing it with fur. Next, he laid a ...
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0answers
98 views

Condemnable limit for the electrostatic field? [closed]

When we define the electrostatic field (law's Coulomb), generated by a $Q$ charge calculated in a point $P$ of the space, we place a particle with a small positive charge $q_0$, called a test charge ...
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4answers
77 views

Electric field of point charge

in above picture, we have two point charge ( same size ). Does electric field of q2 at location of q1 depend on size of q1? because we know when we want to measure electric field of a charge, use ...
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0answers
12 views

Electrostatic force between charges placed in 2 different mediums [duplicate]

Here is the problem. Question: What is the force between the 2 charges? So, If I convert medium 1 into medium 2 keeping the force constant then, (considering an imaginary charge q where the 2 ...
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1answer
76 views

How come subatomic particles interact with each other while not being in contact? [closed]

Although electrons stays away from protons an atom remains electrically neutral But two atoms one positively charged and another negatively charged remain so until they comes in contact. Can the ...

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