# Questions tagged [charge]

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

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### Charge placed asymmetrically inside a cavity in a sphere (conducting)

The question was something like this -> If I have a charge kept inside a cavity made in a sphere of radius $R$ and the radius of the cavity is $r$ where $(r<R)$. Now I do not keep the charge $q$ ...
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### Charge distribution in a sphere in uniform field

So my teacher was telling about how if we place an uncharged conducting sphere inside a uniform electric field , the charges so distribute that the E field inside them becomes zero. He told us that ...
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### Violation of the Law of Conservation of Charge in black hole? [duplicate]

Hey I'm a noob to physics however after reading about black holes and Hawking radiation. If a black hole made entirely out of negatively charged particles (say this black hole is made entirely of ...
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### Equipotentiality of the conductor surface with extra charges sprinkled and Poisson's equation

The electrostatic potential $\phi(x,y,z)$ everywhere on the surface of a conductor/metal is the same. For a quick reference see this post. Hence, any derivative of $\phi(x,y,z)$ must be zero on the ...
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### The force involved in magnetic attraction

Magnetic field causes a force to act on moving charges as in this equation: $F = qv*B$. So what is the force that causes a magnet to attract a charge-less piece of iron? or causes the like poles of ...
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### Why are there $1 / 1.602176634 \times 10^{-19}$ electrons in a coulomb?

Why that exact number of electrons in one coulomb? who decided it? there is nothing wrong with the number, it just seems slightly messy. Why didn't the scientific community just settle on an easier ...
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### What physical quantity remains equal in different frames? [closed]

I recently came across a problem which involved going into rotating frames. And it was pretty tiring. (And difficult..). So I wondered if there was some quantity that you could measure from the ground ...
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### Does a moving charge interact with the magnetic field it produces? [duplicate]

So the title cuts my question a bit short. If a moving point charge produces a magnetic field, does the magnetic field it produces affect it? And let's suppose a moving charge is moving in a region ...
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### How to take the derivative of potential?

The electric potential $\psi$ at a point inside the volume charge distribution is: $$\displaystyle \psi = \lim\limits_{\delta \to 0} \int_{V'-\delta} \rho'\ \dfrac{1}{|\mathbf{r}-\mathbf{r'}|} dV'.$$ ...
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### How shall we show the surface integral approaches a limit (or does not blow up) at a field point near $S'$

Consider the electric field due to volume charge distribution in volume $V'$: $\mathbf{E}=\displaystyle \int_{V'} \rho' \dfrac{\mathbf{r}-\mathbf{r'}}{|\mathbf{r}-\mathbf{r'}|^3} dV'$ The integrand ...
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### Can we use Gaussian pillbox method to determine electric field at a point just near the surface of a surface charge distribution?

I know we can use Gaussian pillbox method to find the discontinuity at the surface of a surface charge distribution. But can we use Gaussian pillbox method to determine electric field at a point just ...
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### Is there a direct evidence for the fact that quarks have fractional charge? [duplicate]

Is there an evidence for quarks having fractional charge? Besides the fact that we know there must be 3 of them inside the nucleons, and the only way that this could happen is if they have indeed ...
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### Work done by battery in moving charge $Q$ in circuit

why work done by a battery in circuit is potential diffrence across plates times charge flown through body. W=Qε(ε is emf of battery) although there are heat and other loses ? and another that my ...
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### Charges on conductor

So i was reading an answer to question Why are the two outer charge densities on a system of parallel charged plates identical? Points that I didn't understand that how come -Q1+x charge can get ...
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### How to fix a charge

How do we fix a charge (positive or negative) in a given position in electrostatics? I know that we assume that we fix a charge by some unspecified force, but what are they? Please explain with some ...
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### What is the radius of the helix a charged particle makes when entering a magnetic field at an angle?

Here is the equation I found in my textbook but it doesn't make sense: $R=\frac{mv\sin α}{QB}$ . Looking at this formula we can say that particle A moving through magnetic field at an angle $α<β$ ...
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### Is it true that any electrostatic charge density can be represented by Dirac Delta function? Give me a general example

My college professor said that any charge density can be replaced by Dirac Delta function but how I want to know.
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### Effect of the magnetic field of a moving charge on the magnetic field used to accelerate the charge

Ok, so my brief understanding is that an accelerating charge will produce a magnetic field. If the charged particle, say an electron is being accelerated by a magnetic field, how does the electron’s ...
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### How to figure out whether a force mediator is $W^+$ or $W^-$ in Feynman diagram?

How to figure out whether a force mediator is w+ or w- in feynman diagram? I always make sure each vertex is zero but sometimes I get my w+ or w- worng.
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### Confusion about electron flow and current

So, I learned in class that current is defined as positive charges moving from south to north. However, in all reality, the negative charges are moving, but the convention of positive to negative wors ...
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### Interaction of an electric field of infinite length [closed]

Question: In a system which prodivides an electric field of an infinite length, if another electric field or particle interacts with it at a certain point, will there be a change at a point infinitely ...
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### Isn't Kirchhoff's junction law a violation of conservation of charge?

As a beginner of classical electrodynamics I am quite confused in understanding Kirchhoff's junction law or it may be the reason that I misunderstood the law of conservation of charge.Please correct ...
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### Induced charges in Electrostatics

How to find the distribution of induced charge on conductor kept in a uniform electric field? Is there a particular method to do the same?
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### Energy density in electrostatics - definition [closed]

Background: It can be shown that the potential energy of charge distribution can be calculated by $U = \frac{1}{2}\int_V \rho(r')\Phi(r') d^3r'$ by means of integration by parts and the poisson ...
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### Collapsing a (General) Simple Quadrupole to line? What are the separations needed to preserve the quadrupole moment?

I was told that simple quadrupoles could be collapsed to a line and I am trying to figure out the dimensions(separations of charges along the line) that would overall preserve the quadrupole moment. ...
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### Calculating the potential difference of a capacitor [closed]

As far as I know the voltage between the plates of a capacitor will be reduced due to discharging. I wonder how much the voltage would be changed if the capacitor lost %25 of its stored energy. ...
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### Could electric charge be a property of spacetime? [closed]

I am always looking for geometric interpretations, and as I understand it, the Einstein field equation basically says 3 things: (1) spacetime is a manifold, (2) free particles follow geodesics in the ...
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### Direction of the current and the electrons [duplicate]

If the electric current is defined as Coulomb/second, why is the direction of the current is just the opposite of the direction of the flow of electrons?
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### What gives an electron its charge? [duplicate]

What exactly gives electrons a charge? I understand how in molecules, an imbalance between electrons and protons give ions charges and I also understand that there is really no positive or negative ...
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### Can I make the visible universe charged by firing short lived charged quantum black holes? [closed]

Imagine I fires a couple of negatively charged quantum black hole and each black hole would last probably a second or two before releasing enormous amount of pure energy, haven't I single handedly ...
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### Infinite field but finite potential Is it possible?

I calculated the electric potential at any point (assuming zero potential at infinity) on the circumference of a uniformly charged ring (non conducting) and after evaluating that integral it turns out ...
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### Surface charge density formula

We know for an infinite plane sheet, electric field from the sheet is given by: $$E = \frac{\sigma}{2\epsilon_0} \hat n$$ Therefore potential is given by  - \frac{ \partial V}{\partial n} = \frac{\...
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### Can we charge an object using cathode rays?

Can we charge an object using cathode rays and use that to charge to repel and object, which is around 500 grams or so...If yes how many coloumbs of charge will it take?
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### Reason for repulsion of like charges

Like charges repel and unlike attract. Like magnetic poles repel and unlike attract. Since electricity and magnetism are fundamentally linked , is this attraction/repulsion due to the magnetic fields ...
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### What does it mean to be/have a negative charge?

what does it mean to be negatively charged. I can't find anything on it and i would love to be able to finally understand what it means to be negatively charged.
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### What is electric field on the surface of a surface charge?

Electric field just near the surface of a surface charge is $\dfrac{\sigma}{2 \epsilon_0} (\hat{n})$ on one side and $-\dfrac{\sigma}{2 \epsilon_0} (\hat{n})$ on the other side. What would be the ...
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### Electric field due to an infinite long, current carrying wire with potential difference $V_0$

I'm confused with the following: I am meant to model a standard co-axial cable as an infinite length of straight wire of radius $a$ symmetrically surrounded by a thin conducting cylindrical shell of ...