# Questions tagged [charge]

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

1,983 questions
Filter by
Sorted by
Tagged with
213 views

### Evaporation of large charged black holes

Black holes evaporate (Hawking Radiation) acting as black bodies with the temperature inversely proportional to the mass. No physical process, be it evaporation or any other "trick", can make a black ...
91 views

### Charge distribution on a hollow conducting cube [closed]

Suppose we have a charged hollow conducting cube, will the charge be uniformly distributed over the surface of the cube? I know that the electric field will be zero everywhere inside the cube but to ...
59 views

### Gauss's Law on Parallel Conducting Plates

I have a question regarding the application of Gauss's law to find the E-fields produced by two parallel conducting plates. My textbook (Halliday and Resnick 9e) states that there is no E-field above ...
179 views

### Contradictions in electric field of infinite uniform charge distribution [duplicate]

This question stems from the exercise 2.50 of Griffith's Introduction to Electrodynamics, which I am rereading. In the problem, he asks to find the charge density of a volume when the electric field ...
72 views

### Why does one Coulomb equal that strange number? [duplicate]

Why is one Coulomb equal to 6.24 *10^18 ? This number is weird . why wasn't it a nice number like 10^20. I have some guesses about this.
102 views

### The value of $E$ in the LHS of Gauss law equation

Suppose there are multiple point charges in a region and I only take the Gaussian surface which encloses only one of the charges $q$. I have read that the $E$ term on the LHS of the Gauss law equation ...
502 views

### What's the explanation of 'paper pieces and comb experiment' about static electricity on atomic level?

I know that the charged comb induces static electricity in the paper pieces.how does that happen? Do the atoms in the paper get ionized,the same what happens when the comb was rubbed on hair?please ...
431 views

### Potential of a non-uniformly charged spherical shell

This question is taken from The Feynman Lectures on electromagnetism. A spherical shell with surface charge density $\sigma = \sigma_0 \cos \theta$ is given. The potential at any external point is ...
43 views

### Benefits and Drawbacks of Swapping Associations of Positivity and Negativity of the Proton and Electron

For historical reasons, I understand that a proton's charge was assigned the label of "positive", the electron's charge was assigned the label of negative, and, crucially, equations of current in E &...
226 views

### Is anything lost by simply saying that a charge is nothing but the divergence of a field?

If we propose that 1) there are fields and 2) that some fields can have places where they converge (that is to say, places where del dot the field is not zero) then we have the definition of such a ...
67 views

### Confusion on negative charges, current, and direction

My text book seems to have two contradictory statements about the same subject. Under the electrical potential and capacitance chapter, it says that negative charges move from lower to higher ...
102 views

### If the speed of electron (in space) is increased, will the magnitude of current also increase? [closed]

Electrons are emitted by a hot filament and are accelerated by an electric field, as shown in the figure. The two stops at the left ensure that the electron beam has a uniform cross-section. (a) ...
83 views

### Charges redistribution in Conducting Plates

Lets Suppose there is Conducting plate X and charge Q is given to which means +Q/2 and +Q/2 on each side . Now lets suppose plate Y (uncharged at first) (exactly similar to plate X (area and material ...
71 views

### Electric field generated by a small object

I've just begun to study electrostatics and I've read the coulomb law, it describes the electric field generated by a point charge as characterized by a spherical shape. I think it is due to the fact ...
776 views

### Energy of parallel plate capacitor

Energy of parallel plate capacitor is defined as $$\frac{CV^2}{2}$$ where V is the potential difference between plates, but shouldnt we need to find the potential energy of each plate due to charge ...
48 views

### Why is it so that some of the paper pieces get stuck to it while others drop instantly when they stick?

When we rub a comb on our head and held it near pieces of paper then they get attracted because of induced opposite charge.
36 views

### Conductance Charged Box

A box with thick and conductive sides with dimensions: Lx, Ly, Lz- while LZ>>Lx,Ly. The long dimension of the box [Lz] can be viewed as infinite so Phi(x,y,z)=Phi(x,y) Given that: Phi(0,y)=-Phi(Lx,...
104 views

### Why is the $\vec E$ field inside a sphere = 0? [closed]

I was taught Electric Field inside a sphere is 0, because of Gauss Law. But inside a uniformly charged sphere, if I go at a distance of $r$ from the centre, I will be closer to the +ve charge and ...
115 views

### Should the electrical charge of $\pi^+$ (positive pion) be considered exact?

According to https://en.wikipedia.org/wiki/Elementary_charge, IIUC, electrical charge of an electron should be considered an exact value of 1.602176634 coulombs instead of an experimental value with ...
219 views

### Change in potential energy of a parallel plate capacitor as a dielectric slab is moved in the space between plates

I was doing this question: If a parallel plate capacitor made of square plates of side L and separation D is connected to voltage source V. And then a dielectric slab of width D is introduced ...
75 views

### How do surfaces charges accumulate?

When a voltage source is applied across an ideal wire, do the push of electric field of battery source causes the accumulation of charges on the surface of wire or the capacitance of wire causes it? ...
46 views

### Electric potential / infinity is not the 0 reference

Let's say we have a charged sphere with radius $r$. Usually, the way we define its potential is $V = kQ/r$. In this way, we have defined its potential with infinity as the zero reference point. Let's ...
55 views

### Why charges should go to the surface of conductor? [duplicate]

How can we show that charges should go to the surface of a conductor, assuming that system should minimize its energy? (With no additional assumptions and maybe using variation method!)
42 views

### Polarized Vs Non-Polarized Capacitors

I am wondering what makes a polarized capacitor physically different than a non-polarized capacitor. I am aware they are functionally different. I understand the physics of a non-polarized capacitor, ...
66 views

### Do $\rho$ and $\vec j$ change in a moving frame?

Consider a cylindrical symmetrical infinite wire with radius $R$. The wire has constant charge density $\rho$ and current density $\vec j$ (pointing to the right). This is measured from the stationary ...
193 views

### Which is more fundamental property of matter: charge or mass? [closed]

I haven't got a whole satisfying answer to this question. I think that matter can exist without charge but it can't exist without mass. Am I correct? So this fact may be answered by asking about the ...
77 views

### BRST Charge in QED

The pure gauge QED Lagrangian density, including the ghost fields, is \begin{align*} \mathcal{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}-\frac{1}{2\xi}(\partial^\mu A_\mu)^2+\partial^\mu\overline{c}\...
30 views

### 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 $q$ ...
48 views

### 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 ...
172 views

### 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 ...
32 views

### 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 ...
58 views

### 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 ...
346 views

### 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 ...
89 views

### 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 ...
140 views

### 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 ...
153 views

### How to take the derivative of potential?

The electric potential $\psi$ at a point inside the volume charge distribution is: $$\displaystyle \psi = \lim\limits_{\delta \to 0} \int_{V'-\delta} \rho'\ \dfrac{1}{|\mathbf{r}-\mathbf{r'}|} dV'.$$ ...
50 views

### 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 ...
62 views

### 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 ...
30 views

### 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 ...
71 views

### 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 ...
66 views

### 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 ...
41 views

### 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 ...
76 views

### 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 $α<β$ ...
141 views

### 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.
13 views

### 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 ...
89 views

### 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.
186 views

### 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 ...
377 views

### 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 ...
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 ...