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 [electricity] tag, as questions about the phenomenon & theory of electricity do not necessarily involve the discussion of fields.

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21 views

How does one derive the electric potential from an electric field?

I'm trying to work through the full derivation to find the equation $$ \underline{E}(\underline{r}) = -\underline{\nabla}V $$ where V is the electric potential and E is the electric field strength. So ...
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23 views

Magnetic field direction [closed]

If the direction of the magnetic force is up along the page or screen and an electron is travelling towards the left along the page or screen, which way is the direction of the magnetic field?
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Why can't I see any bubble in my anode during my electrolysis experiment

I am doing an electrolysis experiment using this apparatus The left side is the anode and the right side is the cathode. I am using two 9v battery in series (total 18V DC) to power my apparatus. ...
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41 views

CRT electron gun

In CRTs, how does the control grid determine the current of electrons when its voltage is very low compared to the anode? And shouldn't it control the velocity of electrons rather than the current ...
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379 views

How does an electric dipole lose its energy while aligning with a uniform electric field?

How does an electric dipole lose its energy while aligning with a uniform electric field--through heat or light?
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Faraday's law of induction applied onto a magnetic film

Situation: Consider an infinite magnetically active film with the film normal in the z-direction and thickness $h$. The dynamic magnetization inside the film is $\mathbf{m}=(0,m_y,0)e^{i\omega t}$. ...
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33 views

Magnetic forces on charges

For a charge that sits in an external magnetic field without moving, why is there no magnetic force on the charge?
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48 views

Problem in finding the divergence at a point [duplicate]

I am solving a problem given as Divergence of $\frac{\textbf{r}}{r^3}$ is a) zero at the origin b) zero everywhere c) zero everywhere except the origin d) nonzero everywhere The answer is given as (...
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Ramsauer–Townsend effect and Thermal Runaway in Thyratrons / (vacuum tubes)

A few years ago an EE told me that the Townsend effect was involved in thermal runaway within vacuum tubes. I can't seem to find any specifics on this on the internet. Can anyone disprove / verify and ...
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Between 2 electrically charged plates, can the speed of particle depend on distance between the plates? (Refer to image)

Now I understand that $\text{work}=KE$ and this will give the formula for speed as $$v=\sqrt{\frac{2qV}{m}}$$ My question is can’t the $V$ be replaced by $Ed$ since $V=E/d$?
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216 views

Angle between dipole moment and Electric field

I was learning the potential energy of a dipole because of torque from Halliday Resnick. In the given diagram, it said that if we move the system anticlockwise then the amount the Work that was done ...
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Are induced electric fields parallel or perpendicular to a conductor?

Suppose you have a conductor embedded in a resistor at a 45 degree angle to the (x,y) coordinate axis, and you apply a time-varying, plane-wave magnetic field in the y direction (see Figure 1). As per ...
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Electric field lines from a non-conductor

I know that electric field lines are perpendicular to the surface of a conductor but I am confused whether electric field lines perpendicular to any surface (non-conductors also)?
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Electrostatic Shielding due to an Infinite Cylinder

If I place a line charge inside an infinite conducting cylinder which is grounded would the outside be shielded from the electric field inside the cylinder. Also would the potential outside the ...
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27 views

Electric Field due to charges inside cavity

Imagine a conducting body as shown: A positive charge +q is placed inside the cavity of the body. Now due to induction a negative induced charge -q has appeared on inside surface of cavity. Is the ...
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Electric field flux through the cubic with surface density of charge [closed]

first of all I want you to excuse me for my level of English. I'm doing a homework on Gauss's law, specifically on how to calculate electric flux through a cubic surface. Below I put the complete ...
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How should one visualize the *electric field* formed from a point charge moving at constant velocity?

So we all know how the magnetic field looks like ( qv x r ) While trying to visualize the electric field I got a little bit confused. Because we are not in electrostatic anymore I don’t know if I can ...
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Electric field outside a dielectric

Been thinking about this(the question) for quite some time. Is it necessary that even in non-symmetrical cases the dielectric medium will not have any effect on the electric field outside it. Although ...
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38 views

Query on Uncertainty Principle

Consider a universe with only 1 electron. We can't know the position and momentum both of this electron, but we can measure the electric field at each point and since the only thing in the universe is ...
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66 views

When do we use the formula $E=kQ/r^2$?

A cube of side 20 cm has its center at the origin and its one side is along the x-axis, so that one end is at x = +10cm and the other is at x = -10cm. The magnitude of electric field is 100 N/C and ...
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1answer
31 views

Proof of electric field intensity due to an infinite conducting sheet

I am reading the proof of electric field due to large uniformly charged sheet. It is give as Consider an elemental strip of width $dx$ at a distance $x$ from point $O$. The linear charge density $\...
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What is the direction of electric field? [closed]

Question: A solid uniformly positive charged hemisphere with radius $R$ has a hemispherical cavity of radius $R/2$ and $C_1$ and $C_2$ are the centres of hemispheres respectively. $C_1P=C_2P=R/4$. ...
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Why the each endpoint has the same electric field at infinity as applying Gauss law of 2 plates?

The 2 conductive plates of infinite length have been placed as above . $\sigma_{1}:=\text{surface charge density of the left plate}$ $\sigma_{2}:=\text{surface charge density of the right plate}$ $\...
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1answer
48 views

Hollow charged spherical shell with charge in the center and another charge outside

I came across this question : A thin metallic spherical shell contains a charge $Q$ on it. A point charge $q$ is placed at the Centre of the shell and another charge $q1$ is placed outside it. All ...
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133 views

Why electric field is scaled by gamma?

Two opposite charges are in a spaceship and are attracted by the electric field $E_s$ But for an observer on earth the Electric force is $$E_e=\gamma E_s$$ Normally the forces are scaled down by $\...
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257 views

Cylindrical coordinates of a ring

A classical problem for electromagnetism students is the calculation of the electric field on the central axis of a ring. It can be solved in many different ways, but I got stuck with the pure ...
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Electric field due to two charged conducting spheres

If we have two conducting charged spheres seperated by some distance, they will interact and assume some form of charge density. Due to this non trivial charge distribution ,the electric field will ...
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Is there a symmetry between scalar and vector formulas for electrostatic and gravitational potential, potential energy, field and force?

Formulas for electrostatic potential, potential energy, field and force, bearing the subscript 'E': Electrostatic potential $V_E=\frac{U_E}{q}$ Electrostatic potential energy $U_E=k\frac{q_1\,q_2}{r}...
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What would be the capacitance of an unequal charged capacitor?

I searched for this question but I cannot get satisfactory answer. Say if we have a parallel plate or cylindrical capacitor and if I supply unequal charge to it how could I find its Capacitance. We ...
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1answer
42 views

Stuck over a problem in electrostatics [closed]

I am stuck over an apparently simple problem that reads: Consider the system in the figure below. An internal sphere of radius $r_1 = R$ is surrounded by two spherical shells or radii $r_2 = 2R$ and $...
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Proca Field Hamiltonian density

Having the most general Lagrangian of the Proca Field given by $$\mathcal{L}=C_1(\partial_\nu A_\mu)(\partial^\nu A^\mu)+C_2(\partial_\nu A_\mu)(\partial^\mu A^\nu)+C_3 A_\mu A^\mu$$ the canonical ...
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39 views

A charge $Q$ is kept at the centre of a thick conducting shell and a point charge $q$ is kept at a distance of $r$ from the centre of the shell [closed]

A charge $Q$ is kept at the centre of a thick conducting shell and a point charge $q$ is kept at a distance of $r$ from the centre of the shell. What is the electrostatic force experienced by $Q$? I ...
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86 views

Evaluating the net force that the southern hemisphere of a uniformly charged sphere exerts on the northern hemisphere

Find the net force that the southern hemisphere of a uniformly charged sphere exerts on the northern hemisphere. I am perfectly aware that this question has been asked many times (here), but I am ...
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Can the direction of electric field in a parallel plate capacitor be tangent to the surface of the plates?

We have two parallel plates connected to a source of emf E, and let's say we introduce a dielectric of constant K, (assume a dielectric slab for simplicity), and we are free to vary the length of ...
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31 views

Electric potential of a circuit (potential difference to be exact)

Electric potential in a space as like as gravity is something understandable but when it comes to circuit I always get puzzled about this. I am looking for help regarding this topic. Is electric ...
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1answer
36 views

Is electric field a property of a charge or is it a spatial distribution of electrostatic force?

I am a bit confused about what gives rise to an electric field. I can look at it in two different ways as follows. When two charges are separated by a distance, the electric field gives the ...
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34 views

Will a stationary charge be affected by changing magnetic field?

We know that changing magnetic fields ($dB/dt \neq 0$) produce electric fields in circular loops. So if we keep a stationary charge in the changing magnetic field, will it experience any force due to ...
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2answers
243 views

Do I need to use Pythagorean Theorem in 3D space for determining electric field induced by an infinite line of charge on a point? [closed]

An infinite line of charge with linear density λ1 = 8.4 μC/m is positioned along the axis of a thick insulating shell of inner radius a = 2.3 cm and outer radius b = 4.9 cm. The insulating shell ...
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33 views

At what point on the $x$ axis is the electric potential zero? [closed]

Could someone help me solve this problem, or provide me with some hint on how to solve it? Two point charges, each $+4.0 \mu C$, are on the $x$ axis; one point charge is at the origin and the other is ...
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1answer
579 views

Question on Gauss's law

This question is from Griffiths' Electrodynamics, Chapter 2, question 49, part e). The question is as follows: Problem 2.49 Imagine that new and extraordinarily precise measurements have revealed ...
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1answer
168 views

Charged plasma and ion grid in interaction in ion thrusters

I was just wondering ..... In this Image of an ion thruster, when the positively charged particles pass through the grids, wouldn't they just bombard the negatively charged grid(a fraction of them). ...
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How to derive the electrical potential of a quadrupole ion trap (Paul trap)?

Currently I am studying the behaviors of an ion in a quadrupole trap (Paul trap), but I just can’t understand that why the electrical potential of this trap is \begin{equation} \phi = \frac{U_0}{r_0^2}...
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Why is the electrostatic force felt in straight lines?

When two positive charges are kept close, they get repelled in the direction of a line joining both the charges. Why is it so? Also, why is the repulsion in a straight path? In both the cases, the ...
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2answers
61 views

Electric field of an electron when r is zero

I know this is a stupid question but according to the coloumb's formula for electric field, if I have a charge right next to another similar charge, such that the distance between them is zero, the ...
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3answers
584 views

How is the $E$-field getting canceled between outer and inner surface of a neutral conducting spherical shell?

I am reading Purcell's E&M book and in one of the example questions, it shows that there is no E field between outer and inner surface after a a point charge is located at an arbitrary position ...
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Macroscopic field as average of microscopic field.(duplicate)

This question has a duplicate but it didn't answer my doubt. I want to know how in Griffith electrodynamics book there is a portion of field inside dielectric where it says the expression we have been ...
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2answers
119 views

Induced electric field due to a long wire

Given an infinitely long wire, carrying a linearly increasing current, what is the shape and direction of the electric field induced by the magnetic field? Given increasing magnetic flux in a ...
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1answer
274 views

Boundary conditions of steady current

Boundary conditions of steady current For steady current we have : $\vec{\nabla}\cdot \vec{J}(\vec{r})=0$ Or $\oint \vec{J}(\vec{r}) d\vec{r}=0$ Then How to prove that: $$\vec{J}(\vec{r})_{1n}=\...
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39 views

Conservative nature of electric field

It's a straightforward question. Electrostatic force is conservative, but I've read that the electric field generated according to Faraday's law of induction is not. What's the difference between ...
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3answers
37 views

Will the coin in the middle of the two opposite charges affect the equipotential lines?

The image shows a coin with neutral charge in between two opposite charges.

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