Questions tagged [charge]

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

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Symmetrical, spherical charge distribution [closed]

I have this problem from my Electromagnetism class, but I don´t have a lot of idea in how to solve it. Show that for a symmetrical, spherical charge distribution $\rho(\vec{r})=\rho(r)$ (with $r$ ...
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Alpha particle moving faster than the speed of light

In this problem I was solving a beam of uniform cross section carrying a current of $0.25\ \mu A$ by alpha particles. The mass of an alpha particle is $m_\alpha=4m_p$, where $m_p$ is the mass of a ...
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Energy Density of Charged Non-Conducting Sphere

I know how the Energy density of conducting and non-conducting shells is derived by using the argument of electrostatic pressure. It comes out to be ½(E²ɛ₀).But when I try to derive it via the same ...
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Superposition principle for the electric field

I had read somewhere that superposition principle is valid for linear functions, but the electric field is not a linear function, then why is the superposition principle valid for electric field?
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What is $Q$ in the energy stored in a parallel plate capacitor?

If we have a parallel plate capacitor like the one below the energy stored in it can be give by $$ U=\frac{Q^2}{2C}$$ $\bullet$ C is the capacitance of the capacitor Now is the $Q$ the free charge on ...
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A solid, insulating sphere of radius a = 4.9cn has a uniform charge density / . Find the magnitude [closed]

A solid, insulating sphere of radius a = 4.9cn has a uniform charge density on its volume of rho = 25.5 muC / (m ^ 3) . Concentric with ( this sphere is an uncharged (بالمركز conducting, hollow () ...
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Conducting shell surronded by, dielectric shell, and an outside $q$ charge

I would like some help with my solution attempt. I have a conducting shell with radius $R1$, surronded by a dielectric shell with $\varepsilon_1$ and radius $R2$, and on the outside i have a $POINT$ $...
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Average electrostatic field over a spherical volume due to a point charge inside

When calculating the average electrostatic field over a spherical volume due to a point charge within the volume, how do we account for the electric field arbitrarily close to the point charge? What ...
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Does the wavefunction depend on the charge? [closed]

The wavefunction (WF) moves at speed $c$ whereas an electron has far more lower velocity. Suppose there is an obstacle and if WF does not depend on charge it will pass in some 'neutral' way around. ...
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Charging of capacitors [closed]

A capacitor with capacity C=10 µF is charged from a battery with ℰ=4.5 V and r=50 mOhm through a semiconductor diode VD whose idealised voltage-voltage characteristic is shown in the figure. U, В is ...
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Does charge always reside at the edge of a conductor's surface

Say I have a circular metal sheet with a charge $Q$ on it do the field lines come out from the edges alone or from across the entire sheet?
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Fault/Technicalities with poynting theorem

When finding the force on a system of point particles $Q_{1}, Q_{2}$, we need to use the formula $$\vec{F} = Q_{1} \vec{E_{2}}$$ Where $\vec{E}_{2}$ is the field ONLY due to the charge $Q_{2}$, since ...
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Discharging two capacitors in series

I have two capacitors, C1 and C2 charged in series and I want to discharge them through a resistor. Does the discharge equation still hold here for each of the capacitor? For C1, $$Q_{1}=Qe^{\frac{-t}{...
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SR for Moving Electrons in Wire

Let's say we have a metal conducting wire with delocalized electrons and positive metal ions. We apply a potential difference across it. Now, the electrons will start flowing in one direction due to ...
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Will the random movement of electrons affect the electric field of a negatively-charged solid conducting metal sphere?

When discussing about a negatively-charged solid conducting metal sphere, We agree on a statement that like charges repel so that the negative charges (aka electrons) are evenly distributed on the ...
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What would happen to charge distribution when two charged, conducting spheres are placed in contact?

I have the following thought experiment. Assume that we have two conducting spheres. Sphere A has a charge of $+ 10 \ \text{C}$ and sphere B has a charge of $+ 8 \ \text{C}$. Now assume that we place ...
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Relationship between volume and surface charge density in the general case

Assume we have surface $S$ enclosing a volume $V$ and assume the only charge present in this setting is located on the surface, given by a surface charge density $\sigma$. My question is about the ...
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Energy stored in capacitor over time

I know that the maximum energy that can be stored in a capacitor is: $$ U = \frac{Q^2}{2\,C}\,. $$ What I am asked is to say how much energy was stored when half of the electric charge that could be ...
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Quantization of Electric Charge and Cutting Spheres

Say you have a metallic sphere that holds a charge $Q$ uniformly. If we cut the sphere into two equal halves, each half of the sphere will hold a charge of $Q/2$. Also, electric charge is quantized. ...
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Distribution of Charges on a Conducting Cup

A multiple-choice problem goes as follows: A small positively charged sphere is lowered by a nonconducting thread into a grounded metal cup without touching the inside surface of the cup, as shown ...
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Gauss' law in the presence of surface charges [duplicate]

Assume $V$ is a volume such that $\rho=0$ in $V$ where $\rho$ is the charge density. Assume further that we have a surface charge density $\sigma$ on the surface $S$ enclosing $V$ such that the total ...
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The multipole expansion of electrostatic potential and large distances

I'm reading Griffiths electrodynamics book and I'm currently studying the multipole expansion of electrostatic potential, and I have two questions if you don't mind: Can I use the multipole expansion ...
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Can we convert momentum to coulombs in any simple sense?

Let's suppose hypothetically you throw a specially shaped magnet designed with sliding plates, and when it hits the ground it converts almost all it's momentum, or if need be for more complications, ...
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How to find the potential difference between two charged spheres? [closed]

Here, the blue sphere (positively charged with $+Q$ charge) is at a lower potential and the pink sphere (positively charged with $+Q$ charge) is at a higher potential, even though they are equally ...
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How does current flow when two charged spheres are connected by a wire?

Here, the blue sphere (positively charged with +Q charge) is at a lower potential and the pink sphere (positively charged with +Q charge) is at a higher potential, even though they are equally ...
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Is this formula for a hollow sphere or a solid sphere?

In the above image, my book has given a formula for calculating the electric potential of a sphere: $$\fbox{$V=\frac{Q}{C}$}\tag{1}$$ Here, $C=\frac{r}{k}$. Is $(1)$ a formula for a hollow sphere or a ...
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What does it mean when we say that an object is neutral?

I am studying electricity and until about now I never really gave much thought to the statement that equal number of proton and electron means neutral charge. Like if we simplify the question and ...
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Inducing charge on an insulator

Can a neutral insulator be induced by a charge kept in its vicinity.if yes,how? Aren't insulators known for having no free(movable) electrons? Or is it due to a translational force on a dipole in a ...
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What are the conserved currents and charges in QFT - operator form of Noether currents?

I can't figure out how to define/compute conserved charges and currents in Quantum Field Theory. I am following Peskin & Schroeder's Introduction to Quantum Field Theory, and in the second chapter ...
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What happens to the positive charges in the cloud after a lightning discharge?

The clouds before a lightning strike contains ice crystal at upper part of the cloud that is positively charged and lower part of the cloud becomes negatively charged. When enough electrons ...
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Is the positive terminal of a Daniell cell positively charged electrostatically?

Suppose, the circuit is open. I understood from @Dale's answer that the negative terminal of the battery is indeed electrostatically negatively charged. Suppose, it can have a charge of $-0.5C$. ...
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Charge in atoms in bond

Let us think of a covalent bond between two atoms $A$ and $B$. Since in covalent bond,sharing of electrons take place, valence eletrons of one atom behave as the electrons of the other atom. So since $...
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Effect of surface contamination on electric field of a charged metal rod

I'm trying to understand how the electric field of a charged metal rod gets affect by surface contamination (i.e. dirt, corrosion, rust, etc.). How would the electric field differ between two metal ...
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2 votes
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Bounded charges density different from zero

From wikipedia, the electric displacement field is $\vec D=\epsilon_0 \vec E+ \vec P$ and it satisfies $\nabla \cdot D=\rho-\rho_b$ where $\rho_b$ is "the density of all those charges that are ...
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Why a body can't have net charge in fraction of a Coulomb?

Q. Quantisation of charge implies:- (a) charge cannot be destroyed (b) charge exists on particles (c) there is a minimum permissible charge on a particle (d) charge, which is a fraction of a ...
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Which charges pushes exactly a charge inside a conductor to the surface and why does it prefer curved surface?

I know this has a lot of questions about it, however my question is different: why does a charged particle inside a conductor get pushed toward the surface? The usual explanation is that in a ...
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Applying Coulomb's law to find the field strength at a point which is not between the two charges involved [closed]

In most of the questions I encountered, I used the coulombs law only to find the force on a particle positioned between two charges. For the question below, I was not sure whether to multiply the ...
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Is the commonly derived Gauss' law for a parallel plate (insulator/conductor) often derived wrong? [duplicate]

I am very confused about plates (conductors/insulators) and applying Gauss law. It seems like gauss law for the isolator is very often derived wrongly. In short: if you have an infinite plate (...
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Do multiple current flows exists in a conductor? Does a slower current provide extra resistance?

If you have a running marathon with lots of people the slower people are in a sense an obstacle for the faster people behind them. The slower people create extra resistance. Is there an analogous ...
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Why isn't electric field null at the midpoint of a straight line connecting two opposite charges of same magnitude? [closed]

**I am confused why the value of the electric field is not null in the midpoint of a dipole as Charge q(A) attracts a negative test charge with the same force of charge q(B) repelling the test charge. ...
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5 answers
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Can positrons attract electrons? [duplicate]

Now, it is established that positrons and electrons have the same mass but opposite charges. Since they have opposite charges, do they create a force of attraction and collide thus annihilating each ...
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Surface charge at the boundary between two dielectric

A point charge q sits at z = −d on the z-axis. Find the polarization charge density $σ_P$ induced on the plane z = 0 when the half-space z > 0 is filled with a medium with dielectric constant $K_R$ ...
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How can recombination lead to photon decoupling if scattering can still occur with neutral particles?

During the recombination era, two things happened: Electrons and protons bonded to form neutral hydrogen atoms. As a result of #1, Compton scattering is no longer efficient enough to keep photons and ...
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Potential calculation in Electrostatic Shielding

I understand that in electrostatic shielding net charge present inside the cavity and the charge induced around it produce no net electric field in the outside region. Is this also valid for electric ...
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Can fundamental particles have magnetic/electric quadrupoles, octopoles, and higher-order moments?

Fundamental particles come with magnetic and electric charge, which makes the particles into a monopole source for the magnetic and electric fields. Of course, the magnetic charge is zero for all ...
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Does it require greater force to accelerate a charged mass than an equal neutral mass?

Accelerating a charge produces radio-waves which is a form of energy. This energy has to come from somewhere. It would seem to suggest it would require greater force to move a charged mass than an ...
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Charge Flow Between Two Spheres Different in Sizes

I'm struggling to understand the following concept: Given two conducting metal spheres of different radii, each have charge -Q (the same charge). If the two spheres are to be connected by a metal ...
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Taylor Couette flow of a charged fluid in a magnetic field

Suppose we have a fluid comprised of charged particles. This fluid, is kept in the annular region between two concentric cylinders, and the inner cylinder is made to rotate with some angular velocity $...
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1 vote
1 answer
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Charge distribution of a spherically symmetric electric potential

Here we have a spherically symmetric electric potential: $$V(r)=\frac{e^{-\lambda r}}{r},$$ and now we want to know the charge distribution which triggers the potential. Of course we can use the ...
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2 votes
2 answers
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Is gauge symmetry necessary for charge conservation?

The common view is that gauge symmetry is necessary for conservation of charge(s) in Yang-Mills theory. But one thing I have never been able to get out of my head is, if there isn't any other possible ...
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