Questions tagged [charge]

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

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surface charge density $\hat{\rho}$ and surface current density $\hat{\mathbf{j}}$

I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th edition, by Max Born and Emil Wolf. Page 5, chapter 1.1.3 ...
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What does the notation $|\text{grad} \ F|$ mean?

I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th edition, by Max Born and Emil Wolf. Page 5, chapter 1.1.3 ...
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Why can't we image an insulating meterial with an SEM?

I know that insulating materials are difficult to measure for insulating materials because there are charging. The effect is a drift or a moving micrograph. Why does charging cause a drift in the ...
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I've got interesting problem from Russian school physics olympiad [closed]

I've been trying to solve this really hard problem (only for me maybe :) from Russian school olympiad for 1 week and I stucked. I tried to make some equivalent electric circuits, but I always end up ...
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I have a doubt regarding electric field inside uniformly charged spherical shell

A spherical shell, uniformly charged, exerts no field inside it ; the point being either at centre or off-centre. According to Gauss law if we construct a spherical Gaussian surface all inside the ...
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Charge transfer in two different metals by touching them

When we touch two metallic conductors one is neutral and other has excess of charges, Case 1- Both metals are of copper, then we can calculate actual charges on them at steady state by capacitance ...
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Magnetic field and frame of reference [closed]

A charged particle moves with a velocity near a wire carrying an electric current,and suppose I see the particle from a frame moving with same velocity in the same direction . I will see the charge at ...
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Negative test charge Electrostatics

Will there be any significant change (if any) in the formulas of electrostatics, if we use a negative test charge in the derivation. thanks for the help appreciate
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Why would the two areas not shrinking together cause the total charge to become infinite?

I am currently studying Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th edition, by Max Born and Emil Wolf. Chapter 1.1.3 Boundary conditions at ...
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2answers
40 views

Why do electrons flow in the opposite direction of the electric field?

I was taught that the potential decreases in direction of electric field but when we place a positive charge in between it's electric field is too in that same direction but the negative charge has ...
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1answer
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Difference between ions, free electrons, and excess charge

This part from University Physics turned my world upside down. What is the difference between ions, free electrons, and excess charge? Also, ions and free electrons make up a neutral conductor? Bloody ...
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Battery as charge separating factory

I like to think of electric battery as charge separating factory (similar to Van de Graaff generator). I took this idea from "Matter and Interactions" by Chabay and Sherwood. With this view ...
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Why doesn't a chemical reaction occur with the movement of electrons in the context of electricity?

In school it is generally taught that the movement of electrons between two atoms causes a chemical reaction. However, when it comes to electricity why doesn't a chemical reaction occur with the ...
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Electric potential energy between fast moving charges

It is well known that in static system, electric potential energy of system conducted with two sphere charges, $q_1$ and $q_2$ with distance $d$ and radius $R$, is $E=\frac{q_1 q_2}{4\pi\epsilon_0 d}+\...
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Charge produces which one: Field or Potential

Is it correct to say that when a charge is at rest, it produces field and potential, or does it produce potential and because of the potential dfference, there is a field? Are both of these ...
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Correct relationship between the electric field and voltage at a distance from point charges [closed]

Hello I'm wondering if this is a correct understanding of the electric field and voltage strength as a function of distance. I'm helping a fellow student with their homework and I don't want to say ...
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Why is the value of volume charge density $ρ$ zero in lossy medium?

Given is the page of a book which I was studying. I was trying to study the derivation of the wave equation in a lossy medium. As I have underlined a sentence that says, "most of the case in ...
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Self-energy of hollow sphere [closed]

In the derivation I've seen, to find self energy for a hollow sphere people do $ \int V dq$ and say that potential to bring a charge to boundary of hollow sphere is always $ \frac{kQ}{R}$ where $R$ ...
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Can separating the plates of a charged capacitor create quantum entanglement?

If you take the case of a parallel plate capacitor with air as a dielectric, it's my understanding that separating the plates increases the voltage between the plates proportional to the distance and ...
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Charge density in thermionic emission

How can I calculate the charge density that is emitted by a hot filament by Thermionic emission? I was thinking of using this equation since I know the current density and the velocity of the emitted ...
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Interpretation of Gauss's theorem applied to Maxwell's equations: $\dfrac{d}{dt} \int \rho \ dV + \int \mathbf{j} \cdot \mathbf{n} \ dS = 0$

Using Maxwell's equations and Gauss's theorem, we get $$\dfrac{d}{dt} \int \rho \ dV + \int \mathbf{j} \cdot \mathbf{n} \ dS = 0,$$ where $\rho$ is the electric charge density and $\mathbf{j}$ is the ...
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What is the meaning of $\rho _b$ blowing up at the surface?

In Griffith's it has been said that while deriving the equation $\nabla\cdot D=\rho_f$ where $D\equiv\epsilon_0E+P$ and $\rho_f$ is the free charge, there has been no mention of the surface bound ...
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Electric field and potential in a point inside conductor for a particular case [duplicate]

Lets say we have an irregularly shaped conductor with a random cavity inside it and a charge +q outside the conductor. Now I have to find the potential inside the conductor due to induced charges on ...
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How does the force of charge between particles change with velocity?

I'm sure how fast a particle moves must have some relativistic effect, or maybe also classical ones too. Suppose you fixed the positions of two charged particles. Suppose you're in a lab frame and in ...
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Dipole moment formula for charges with unequal magnitude

Consider a semi circular ring with radius R and charge Q distributed uniformly on the ring boundary and now, -Q charge is introduced at the centre ( q=Q) Now what I did was I split the ring up into ...
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Change in distribution of charge on plates of capacitor on earthing one plate

If we consider the following situation: Now the capacitors are already charged so the potential difference between the plates is well defined but the absolute potential isn't. So what will happen if ...
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The misleading thing about this picture of capacitor

If my understanding of capacitance is correct, capacitance $C$ is defined as the ratio $\frac{Q}{V_{ab}}$ where $Q$ is the magnitude of charge on each conductor for two oppositely charged conductors, ...
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Can we create a potential difference across the ends of a metallic rod just by accelerating it?

If we take a metallic rod and accelerate it then what would happen? My view is that, as a metal has a sea of free electrons flowing about these free electrons will experience a pseudo force and will ...
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What change does $dQ$ represent in definition of current $i$

The definition of current $i$ is $$i=\frac{dQ}{dt}.$$ According to calculus whenever we write one variable as a derivative of another variable that simply means we are trying to calculate the rate of ...
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Current density vector clarification

I have some basic doubts about current density vector $\vec J$, which is defined as "the vector whose magnitude is the electric current density, and whose direction is the same as the motion of ...
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1answer
63 views

Finding the charge on a capacitor plate

In a question, the left plate of a capacitor carried a charge Q while the switch was off; When the switch is closed and the current stops flowing again, you're supposed to find the final charge on ...
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Is superposition of charge possible?

Maybe majorana fermions could exist but is very different from both quasi particle pair and particle hole pair, it could have both positive and negative charge in superposition until it is being ...
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Doubt regarding grounding of a sphere and charge distribution [closed]

An insulated sphere with dielectric constant $K$ (where  $K>1$) of radius of $R$ is having a total charge $+Q$ uniformly distributed in the volume. It is kept inside a metallic sphere of inner ...
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Electric Work and Electric Potential [closed]

Could someone answer this with an explanation? I have a guess that it is the third path that requires the most work since it is the longest and most zig-zaggy of them to reach point b, but I'm not ...
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How long can static charge stay on a material?

When a material/body gets charged, the charge can be discharged by conduction. What if the charged body is place in a vacuum where the charge can't be discharges through air, how long can the charge ...
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Is electricity really the flow of electrons or is it more involved?

I am new to the physics category of the Stack Exchange site. I apologize if my question is wrong, too broad, simple, or worded incorrectly. I am just trying to figure out what is true and false when ...
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Global and gauge charges

I have seen several questions regarding the difference between global and gauge charges, but I don't really get the physical implications. The sQED lagrangian is: $\mathcal{L}=-\frac{1}{4}F_{\mu \nu}^...
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Is it possible, that just as a boson of mass exist (Higgs boson) a boson of charge exists as well? [closed]

If that is the case would it be possible for those bosons to interact with other particles directly? Meaning the field associated with those bosons, interact with the field associated with other ...
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How to decide which way are the limits of an integral?

So, I'm trying to calculate the electric field at a point $r$ distance away on the perpendicular bisector of a finite line charge having uniform charge density $\lambda$ I arrive at the following ...
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2answers
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Computation of the electric potential of a point charge with Dirac delta

As you know, the electrostatic potential for a point charge in free space (at the position $\vec {r_0}=x_0\hat {x}+y_0\hat{y}+z_0\hat{z}$) is given by the relation: $$V(\vec r)=\frac{1}{4\pi\epsilon_0}...
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Can electrostatic induction occur between two equal potentials?

Referring to a situation like shown in this basic diagram of electrostatic induction: Does electrostatic induction occur if you have charged objects on both sides of a grounded conductive sphere like ...
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1answer
62 views

Does there exist charged BTZ black hole analogue in 1+3D with a negative cosmological constant?

BTZ black holes are defined for the case of 1+2D gravity theory because of closed form computation. I’m wondering if there exist a $1+3D$ analogue black hole? Edit: What I'm actually looking for is ...
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If charges is quantised, how can we use integrals in electrostatics?

In electrostatics we say that charge is quantised. Then my question is how can we integrate them?
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If a capacitor is placed inside a uniform electric field (independent of the capacitor), will the formula $U = Q/C$ still hold?

Suppose we have a plate capacitor, placed in a uniform background electric field (in a way that the electric field is perpendicular to the capacitors plates. Without the electric field, the ...
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Charge tends to accumulate at sharp points

This example is from the book Concepts of Physics by HC Verma. The same example is also present in the book - Fundamentals of Physics by Resnick, Halliday & Walker. Consider two spheres $A$ and $B$...
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Is there an expression for resistance in a circuit derived from Coulomb's Law?

Coulomb's Law states that the repelling force felt by two charges is proportional to the magnitude of their charges and inversely proportional to the square of the distance between them. Defining ...
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Formal definition of charge density and current sources in classical electromagnetism

Charge density and current sources are fundamental to classical electromagnetism and appear in Maxwell's equations and everything that comes after. They are intuitive, charge density is a scalar field ...
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Positive mass but negative/positive/neutral charge

I have heard that the mass of a particle can't be negative because the hamiltonian should be bounded from below. What is the formal argument regarding this and why the same argument doesn't follow ...
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Changing the convention of positive and negative charge holders in an atom

Would there be any specific change in the physical/chemical laws if one day we changed the convention that electrons are negatively charged to the one that electrons are positively charged and vice ...
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Charges on conductors [closed]

Suppose two similar conductors which are unequally charged are brought close to each other,then charges from one will flow to another and ultimately both of them will be equally charged and either ...

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