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Questions tagged [charge]

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

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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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2answers
34 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.
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10 views

Capacitance of Three Metalic Cylinders [on hold]

Three concentric, thin, long conducting cylindrical shells have radii of 12, 47, and 137 [cm]. The space between the shells is filled with air. The innermost and outermost cylinders are connected at ...
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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

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

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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Problems in calculating potential of uniformly charged infinite plane or wire

From $\int_Vd^3x \rho(\vec x)\mathrel{\mathop{=}\limits^!}Q_V$ and by use of Dirac's delta distribution one finds that the charge density for the uniformly charged infinite plane is $\sigma\cdot\delta(...
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Charging capacitor in an incomplete circuit [closed]

I have 2 confused questions regarding the below circuit. please help me out How will the capacitor even charge in the following scenario when the right side of the capacitor is not connected to ...
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How is the charge conserved at the up to anti-down vertex?

I can see how the charge is conserved in the overall diagram but I can not understand how it is conserved at the up to anti-down vertex.
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36 views

Electric potential and voltage

A capacitor is connected to a battery with constant voltage. If you approach one of the plate to the other, what happens to electric potential? I already have an answer to this question but it's ...
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1answer
52 views

Finding the maximum value of electric field

Suppose you have a surface of finite area with a fixed surface charge distribution. Does a maximum electric field magnitude $|\vec{E}|_{max}$ exist for each and every possible surface area? If yes, ...
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1answer
26 views

How can we analyze electronic capacitors in series? [closed]

Two capacitors are in series, such as in this circuit diagram: When doing a circuit analysis, how can we describe the voltages and charges across the two capacitors?
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2answers
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Spherical surface charge distribution [closed]

I have a problem that sounds like this: Consider a spherical surface of radius $b$ with the fixed charge distribution $\sigma(\theta)=\sigma_0 \cos(\theta)$, $\theta$ being the polar angle. ...
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1answer
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What is the volume charge density (in spherical coordinates)?

What is the volume charge density (in spherical coordinates) of a uniform, in finitesimally thin spherical shell of radius $R$ and total charge $Q$, centered at the origin? Give your answer in terms ...
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2answers
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How to find direction of Electric field lines due to infinite charge distribution?

I saw in my textbook while calculating Electric field due to a uniformly charged conducting solid sphere the direction of electric fields were taken radially outward. How can you justify this? There ...
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QM: Local phase shift in wave function

Local phase invariance ultimately lead to charge conservation but When does a local phase shift occur in a wave function?
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Prove electric field is continuous at an external point $P$

I have a continuous charge distribution with density $\rho$. Can anyone please tell how shall I prove the electric field is continuous at an external point $P$? $\displaystyle \mathbf{E}=\dfrac{1}{...
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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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1answer
49 views

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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1answer
58 views

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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1answer
200 views

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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1answer
28 views

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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3answers
63 views

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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1answer
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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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3answers
57 views

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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1answer
45 views

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 ...
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1answer
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How to contain air ions inside a chamber without loosing their charge?

I would like to create an experiment where I would hold ionized air molecules. Most likely negative O2-1 ions. I am looking for the most appropriate enclosure so that the ions do lose as little of ...
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1answer
38 views

What is dipolar charge distribution?

An electric dipole is a system of two opposite point charges when their separation goes to zero and their charge goes to infinity in a way that the product of the charge and the separation remains ...
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2answers
21 views

Location of free charge in insulators

I'm going through the introductory section to Electrostatics in Materials in Griffiths, and I have a question that I can't seem to find a satisfactory answer to. If I have an insulator with free ...
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2answers
118 views

Electrostatic values where there are some charge

I've started asking myself: What is the value of the electric field at the surface of a shell with uniform distribution? In particular, is it infinite, as this point is over an (infinitesimal) ...
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Weak hypercharge physical existence

How do we know that electrons are chiral? Even if left-handed electron carries weak hypercharge, it's only for an infinitesimally small time or is it predicted by QFT?
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1answer
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Charged particle in uniform Magnetic field

How can charged particle have constant kinetic energy in uniform magnetic field. I mean particle is accelerating so it must radiate EMW and loose energy?
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1answer
71 views

Point charge inside a hollow conductor, does the exterior field changes when the charge moves?

Suppose that I have a hollow conductor with no specific format. I know that if I put a charge inside it, it will induce charge in the inner surface and on the outer surface a charge with a opposite ...
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1answer
60 views

My hairs on my hand stand straight whenever I move my hand to TV screen and feel vibration and sound on TV screen

Whenver I try to reach my hands near the screen of my TV . My hairs on my hands get straight and more importantly I can hear and feel a sound and kinda vibration . Please mention if this sound ...
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0answers
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Proving continuity of potentials and fields due to a surface charge

Is there a way to show: $(1)\ \displaystyle \phi=\int_{S'} \dfrac{\sigma}{r} dS'$ is continuous all over space $(2)\ \mathbf{E}=\displaystyle\int_{S'} \dfrac{\sigma}{r^2}\ \hat{\mathbf{r}}\ dS'$ is ...
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1answer
71 views

3 repelling parallel line charges

Addendum 1 (Illustration added at the beginning): Suppose I had 3 identical parallel line charges parallel to the x-axis of infinite length in the same geometric plane. The first and third ...
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569 views

What is the electric potential inside a point charge?

We know that electric potential of spherical charge is inverse proportion with $r$ from $V = \frac{kq}{r}$ , So if $r$ is getting less then electric potential will be higher. But , What about point ...
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1answer
52 views

Why does the Voltage of a Capacitor change in an alternating current (AC)?

I have a question about charging a capacitator in an alternating current. If the process starts the current charges the capacitator, therefore the voltage on the capacitator will be increased. Now the ...
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1answer
57 views

Electromagnetic Mass [closed]

Planck introduced a variant/correction term of Einstein’s mass-energy equivalence of the form $E_0 = mc^2 + PV$ The pressure is related fundamentally to a number of terms related to the temperature ...
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0answers
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Integrand discontinuity of surface integral of electric field of dielectrics

I am reading an article here on dielectrics Equation $(4.10)$ is: $$\Phi(\mathbf{r})=\dfrac{1}{4\pi \epsilon_0}\int_{V} \dfrac{d^3r'}{|\mathbf{r}-\mathbf{r'}|} [\rho (\mathbf{r'})\ -\nabla'.\mathbf{...
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2answers
63 views

Moving a charge and potential energy

When talking about bringing a charge from a reference point to another point, we consider the work done by an "operator" force opposite to the electric one, but wouldn't that just cancel the ...
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1answer
60 views

Why does my finger not conduct electricity when I press on my laptop case?

I have an aluminium laptop and when it is plugged in and I brush over the case I feel a small tickeling when brushing lightly on the case. I have read that is coming from grounding issues and this ...