Questions tagged [electric-fields]

For questions that utilize the concept of electric fields (commonly denoted by the letter E), or for questions whose answers likely involve electric fields. More specific than the [tag:electricity], as questions about the phenomenon & theory of electricity do not necessarily involve the discussion of fields.

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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,...
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Why is the $\vec E$ field inside a sphere = 0?

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 ...
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1answer
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$\nabla. \vec E =\frac{\rho}{\epsilon}$ for a non conservative field

$$\nabla\cdot \vec E =\frac{\rho}{\epsilon}$$ In this formula, suppose I have a non conservative $\vec E$ field, and I put this formula into this expression I will get a corresponding value of $\rho$....
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Can an electric field be detected around a large black hole? [duplicate]

There is an existing question Why can an electric field escape from a black hole? which has a complex answer, not accessible to the layman. The point of this new question is that the electromagnetic ...
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Electric Field around a avalanche beacon?

I'm currently working on a scientific work regarding electric fields created by avalanche beacons. My question is what kind of field is created around the antennas of such device? Is it a dipole (2 ...
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Hard problem on dipole with $r^7 $ in denominator, I don't know how or why?

In an external electric field, a molecule is polarized. The dipole moment induced is given by $\vec P =\alpha \vec E$, where $\alpha$, is the polarizability constant and is a positive constant and $\...
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39 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? ...
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Field due to a disc at a general point

I have recently studied electrostatics in school and we learnt to calculate the electric field at a point on the axis of the disc. We were told that calculation for a general point is beyond our ...
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Why do we add the flux operating in 2 different regions for finding electric field due to sheet of charge

For sheet of charge Applying gausses law Flux =E.ds = q•/E• Contructing cylindrical gaussian surface The curved part does not contributes towards flux cz ds is perpendicular to E so cos90°=0...so ...
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Electric field inside infinite charged hollow cylinder

Gauss's Law says that electric field inside an infinite hollow cylinder is zero. My question however is that an infinite hollow cylinder can be constructed by taking rings as element and the field ...
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Number of points where the electric field is zero

Three point charges of equal magnitude are placed at the corners of an equilateral triangle find the number of points where the electric field is zero. this was a question that one of my friend had ...
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ELECTROSTATICS (STATIC CHARGES) [closed]

A uniform electric field points to the left. A small metal ball charged to -2 µC hangs at a 30° angle from a string of negligible mass, as shown in the figure 2.2. The tension in the string is ...
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Why do electrons accumulate on the surface of a wire (along its length) when a voltage source is applied across the wire cross section?

When I was going through how electric fields are transmitted long distances through a wire, I read that there was accumulation of charges along the surface of the conductor to drive the fields to long ...
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Electric field inside and outside a hollow spherical shell

If a charge(+q) is placed at distance away from a hollow spherical conducting shell , would the net electric field inside the hollow portion remain zero? If the +q charge was placed anywhere inside ...
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Problem in understanding superposition principle in electrostatics

When I have a single charge, it produces a electric field and a test charge will experience a force. Now when I have two(identical,same sign) charges, they produce electric fields and when the test ...
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What is the electric field between two coaxial conducting cylinders when a charged sphere is placed within the inner cylinder?

A long cylindrical capacitor of length $l$ consists of an outer conductor of radius $a$ and an inner conductor of radius $b$, where $l>>a$. The outer conductor is earthed, and the inner ...
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1answer
32 views

Conductive sphere surrounded by conductive shell kept at constant potential

I am studying electromagnetism and I am a bit confused about the following problem: We have a charged ($+Q$) sphere (radius $R_0$) surrounded by a conductive shell (radius $R_1$ and $R_2$) which we ...
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Velocity Selector Question with Unknown Voltage

In a diagram, electrons are emitted from a hot coil with initial velocity 0 at plate A and then pass through a uniform field between two plates (A and B) where $V=1.00\times10^4$ volts. After, they ...
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Why doesn't shell theorem work here?

I think I have a misunderstanding about the shell theorem regarding electrostatics here. Since we have a conducting spherical shell, and we are looking for the $E$ field, shouldn't it be 0 within ...
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1answer
29 views

Electric field conservation

I was reading on the topic electric field at that time i came up with a question "why electric field is conservative in nature? ". Then i searched it on google but it has been given in terms of work ...
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1answer
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The electric and magnetic field, reaching to infinity

I have difficulty’s to accept that the electric and magnetic field components of photons as well as of electrons and the other subatomic particles are extended to infinity. For practical use that does ...
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1answer
40 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 ...
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1answer
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Voltage calculation at any point between two plates at different voltage

I have two plates (actually they are electrical connectors on a board) and I try to find the way of getting the $V$ value at any point between two plates, $A$ and $B$. A is at $V_o$ (in my case it is ...
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How flux density increases in the dielectric medium?

The above figure shows a polar dielectric medium in an external electric field which is normal to it's surface. From the equation of D(electric flux density) we see that flux density increases but ...
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How can electric fields be used to detect cracks in metals? [closed]

My physics teacher brought this up in a lecture and I am not exactly sure what he is saying.
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Can electric field lines form close loops [duplicate]

I was reading on wikipedia about electric field lines In the Precise definition part it says it can form close loops but Kelvin–Stokes theorem it's written it cannot be closed loops.(My teacher too ...
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Confusion in least action in the following situation

I understand that when electric field is applied normal to the surface of a conductor the net electric field inside the conductor is zero. But as shown in the diagram above, if electric field is not ...
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Direction of electric field in the following cases?

In the above figure if applied electric field is at angle(but not normal) to the surface and is limited only to a specific region as shown, I believe the Electric field due to the induced charges ...
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2answers
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About the electric flux at various part of the cube [closed]

A point charge +q is placed at the centre of a cube of side l. What will the electric flux at one of its sides be? How will the flux change if the charge is put on a corner?
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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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4answers
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What is an electric field?

I know that we can define electric fields by the influence they have on certain kinds of matter (in particular, the charged kind), and that they store potential energy, but my question is what ...
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3answers
63 views

How can you use the potential to find the electric field? [closed]

Lets say we have the above system of point charges. We were asked to find the electric field at the centre. Superposition of electric fields gives the right answer, but how can we do it by ...
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The electric field of conducting and non conducting sheets

When a non conducting sheet is charged , the electric field due to it is half the electric field due to a charged conducting sheet. How exactly do they differ? When we use gauss law using a Gaussian ...
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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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1answer
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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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1answer
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What happens with the divergence of maxwell stress tensor when EM fields in vacuum?

The conservation momentum can be derived from the total electromagnetic force on the charges in volume $V$ and is written in this way: $$ \frac{d\vec{p}_{mech}}{dt} + \frac{d}{dt} \int_V (\vec{E}\...
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Question about polarisation in dielectrics

I was going over my elecro statics course and in a textbook it gave an explanation on how molecules in a dielectric are polarised when placed in an external electric field. Diagram: They seem to be ...
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What is the field that moves charges in a resistor?

We say a potential difference moves charges in a resistor.. i want to understand it in terms of field. What charge distribution produces a field in the resistor? True, the cell produces a field.. but ...
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1answer
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Is electric force constant all over the surface of a conductor?

This question was asked in IIT JEE 2010. I know that the electrostatic pressure is equal to (1/2)∈(E)² and if we multiply this with the projected area then we would get the force acting on an object ...
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Is the electric field arrangement in photon fixed? [closed]

When we measure a photon's electric field (let's take a visible light photon) then do we observe the electric field's direction first, let's say, upwards then downwards? Or is the detection of both ...
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1answer
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Physical Relation in Maxwells Equations of quantity between as well as fundamental forces

Recently learnt about Maxwells Equations, am wondering what is the physical relation between electric field E and magnetic field B. It would help if the physical meanings are related to the ...
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1answer
39 views

Electric Field calculation [closed]

What are the limits(lower and upper) of electric field of the differential element in the calculation of electric field of some standard configuration Eg: electric field calculation for spherical ...
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1answer
47 views

Why should there be electrostatic equilibrium inside a conductor? [duplicate]

I have been trying to understand why the net electric field inside a conductor is zero regardless of the exterbal electric field. But why should equilibrium ever be attained?
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Work done in moving a charge in circuit?

Why is the work done in moving a charge from one point to another in a circuit through any path the same even though heat and other losses are there?
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4answers
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Can every mass obey the Newton's 3rd law?

As in, if we were able to produce a very huge amount of force on a very small body, would it push back with the same force? Given it doesn't break or disintegrate. Like if we electromagnetically put ...
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3answers
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Why do my books introduce the equation $\nabla \cdot \mathbf{E}=\frac{\rho}{\epsilon_0}$ without showing partial derivatives of $\mathbf{E}$ exist?

In electromagnetism (electrostatics), we often come across the equation $\nabla \cdot \mathbf{E}=\frac{\rho}{\epsilon_0}$. In order for this equation to be meaningful, $\mathbf{E}$ must be a ...
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Why is electric field $E^i = E_i$ instead of $E^i = - E_i$?

Let us consider the Minkowski spacetim. Generally, we know that when we lower or raise the index of the convariant or contravairant tensor, we need to use the metric $\eta^{\mu \nu}=\eta_{\mu \nu}=(+,...
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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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Is it possible to calculate force acting on water in electric field?

I know, that when water is placed in an electric field a force is acting on it because of polarization. Is it possible to calculate this force with taking the brownian rotation of the molecules as ...
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Where am I going wrong in deriving Maxwell's first equation in differential form?

By denoting the source coordinates with prime, I get flux through a closed surface: $$\Phi= \displaystyle\oint_{A} \mathbf{E}(x,y,z) \cdot \mathbf{\hat{n}}\ dA =q (x',y',z')$$ And now using the ...