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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In electrostatics, why the electric field inside a conductor is zero?
In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.
I ...
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How is it possible to accelerate a neutron?
It is possible to accelerate a charged particle in an electric field, how is it possible to accelerate a neutron? How can we control its velocity?
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Why is electric field strong at sharp edges?
I learned about the coronal discharge, and the common explanation is because the electric field is strong where radius of curvature is small. But I haven't found anything yet that explains why ...
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Can someone please explain magnetic vs electric fields?
I've looked through about 20 different explanations, from the most basic to the most complex, and yet I still don't understand this basic concept. Perhaps someone can help me.
I don't understand the ...
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Difference between electric field $\mathbf E$ and electric displacement field $\mathbf D$
$$\mathbf D = \varepsilon \mathbf E$$
I don't understand the difference between $\mathbf D$ and $\mathbf E$.
When I have a plate capacitor, a different medium inside will change $\mathbf D$, right?
$\...
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Why does the density of electric field lines make sense, if there is a field line through every point?
When we're dealing with problems in electrostatics (especially when we use Gauss' law) we often refer to the density of electric field lines, which is inversely proportional to the radius in the case ...
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Can lightning be used to solve NP-complete problems?
I'm a MS/BS computer science guy who is wondering about why lightning can't (or can?) be used to solve NP complete problems efficiently, but I don't understand the physics behind lightning, so I'm ...
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How does energy flow in a circuit? Which is correct?
I have been very interested in this question since reading Electricity Misconceptions by K-6
There are two perspectives I have come across for how energy flows in a circuit:
Electrons carry charge. ...
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What are the fields produced around a current carrying conductor?
If you consider a current carrying conductor, every instant an electron enters the conductor, another electron will be leaving the conductor. Thus, the current carrying conductor will not be charged (...
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Why is there no gravitational magnetic field? (Or, is there?)
We can think that the electric field and the gravitational field operate similarly in the sense that the forms of their governing laws (namely, Coulomb's law and Newton's law respectively) are ...
user87745
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Are Maxwell's laws mathematically precise?
Electrodynamics makes heavy use of vector calculus, which in turn is about differentiation and integration of scalar and vector fields in $\mathbb{R}^3$. At this point everything seems fine to me, ...
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How is energy "stored in an electric field"?
My physics teacher told me the statement "The energy of a capacitor is stored in its electric field".
Now this confuses me a bit. I understand the energy of a capacitor as a result of the ...
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Detection of the Electric Charge of a Black Hole: How can an electromagnetic field escape the event horizon of a Reissner-Nordström black hole?
By the "No Hair Theorem", three quantities "define" a black hole; Mass, Angular Momentum, and Charge. The first is easy enough to determine, look at the radius of the event horizon and you can use the ...
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Why is there an electric field in a wire even though it is a conductor?
If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right?
Yet, why does the same not hold ...
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Paradox with Gauss' law when space is uniformly charged everywhere
Consider that space is uniformly charged everywhere, i.e., filled with a uniform charge distribution, $\rho$, everywhere.
By symmetry, the electric field is zero everywhere. (If I take any point in ...
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What force particle mediates electric fields and magnetic fields?
The force carrier for magnetic fields and electric fields are supposedly photons. I don't get it:
1) Wouldn't that mean that a charged particle (e.g. an electron or even a polarized H2O molecule) ...
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How can neutral atoms have exactly zero electric field when there is a difference in the positions of the charges? [duplicate]
It is said that atoms with the same number of electrons as protons are electrically neutral, so they have no net charge or net electric field.
A particle with charge cannot exist at the same position ...
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"Find the net force the southern hemisphere of a uniformly charged sphere exerts on the northern hemisphere"
This is Griffiths, Introduction to Electrodynamics, 2.43, if you have the book.
The problem states Find the net force that the southern hemisphere of a uniformly charged sphere exerts on the northern ...
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Can a magnetic field exist without an electric field present?
I know an electric field can exist without a magnetic field as in the case where you have a stationary point charge.
But, magnetic fields are created by moving charges so wouldn't you always need an ...
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What is the electric field in a parallel plate capacitor?
When we find the electric field between the plates of a parallel plate capacitor we assume that the electric field from both plates is $${\bf E}=\frac{\sigma}{2\epsilon_0}\hat{n.}$$ The factor of two ...
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Field between the plates of a parallel plate capacitor using Gauss's Law
Consider the following parallel plate capacitor made of two plates with equal area $A$ and equal surface charge density $\sigma$:
The electric field due to the positive plate is
$$\frac{\sigma}{\...
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What happens when we connect a metal wire between the 2 poles of a battery?
As I remembered, at the 2 poles of a battery, positive or negative electric charges are gathered. So there'll be electric field existing inside the battery. This filed is neutralized by the chemical ...
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Why does the voltage increase when capacitor plates are separated?
In lab, my TA charged a large circular parallel plate capacitor to some voltage. She then disconnected the power supply and used a electrometer to read the voltage (about 10V). She then pulled the ...
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Electromagnetic fields vs electromagnetic radiation
As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same ...
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Does a current carrying wire produce electric field outside?
In the modern electromagnetism textbooks, electric fields in the presence of stationary currents are assumed to be conservative,$$
\nabla \times E~=~0
~.$$ Using this we get$$
E_{||}^{\text{out}}~=~E_{...
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Why doesn't the voltage increase when batteries are connected in parallel?
Can you please explain the thing below?
When we add a battery in circuit then, it gives out some electric field that moves through the circuit and gives a force on electrons in conductor to produce ...
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Do extremely high-voltage power lines emit positrons?
Stretching across China, from the Xinjiang region in the west to the province of Anhui in the east, there's a ±1,100 kV high-voltage direct-current transmission system. I'm not 100% sure what "±1,...
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Purpose of Using Taylor Series and Multipole Expansion to Approximate Potential
I'm currently taking a third-year electromagnetism course (we use Griffiths), and we have begun covering approximations of our potential function, $\text{V} =\int\frac{k \text{dQ}}{\textbf{||r||}}$, ...
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Are the plates of a battery really charged?
In a zinc/copper Daniell cell correct me if I am wrong :
Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper which needs 2 to complete its valence shell....
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Why is the field inside a conducting shell zero when only external charges are present?
In many introductory books on electrostatics, you can find the statement that the field inside a conducting shell is zero if there are no charges within the shell. For example, if we place an ...
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Why can't electrostatic field lines form closed loops?
My physics textbook says "Electrostatic field lines do not form closed loops. This is a consequence of the conservative nature of electric field." But I can't quite understand this. Can anyone ...
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How is the curl of the electric field possible?
Taking the curl of the electric field must be possible, because Faraday's law involves it:
$$\nabla \times \mathbf{E} = - \partial \mathbf{B} / \partial t$$
But I've just looked on Wikipedia, where it ...
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Does a Faraday cage block magnetic field?
I want to block the magnetic field of a very strong magnet, can I put it inside a Faraday cage to block its magnetic field?
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Reduction of Maxwell's equations to classical circuit theory
Can classical circuit theory based on lumped element models be obtained from Maxwell's equations as a limiting case in an appropriate sense?
If this is the case, what exactly are all the assumptions ...
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What is the physical meaning of the energy density of an electrostatic field?
I understand the physical meaning of electrostatic energy of a system of charges (or a distribution with given density) as the energy stored in the system while working to carry the charges from ...
user6452
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Why do electric field lines curve at the edges of a uniform electric field?
I see a lot of images, including one in my textbook, like this one, where at the ends of a uniform field, field lines curve.
However, I know that field lines are perpendicular to the surface. The ...
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Why can two (or more) electric field lines never cross?
The the title is self explanatory, I guess.
Why can two (or more) electric field lines never cross?
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How can electric field be defined as force per charge, if the charge makes its own, singular electric field?
The electric field $\bf{E}$ represents how much force would act on a particle at a certain position per unit charge.
However, if we actually place a particle in that position, the electric field will ...
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What is the difference between an electric and a magnetic field? [closed]
This question is a consequence of another question of mine which is about spin.
Here is my spin question.
What is the difference between these two fields? How do they occur? Am I right if I say that ...
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What does the complex electric field show?
We have a complex electric field. Is there any definition for absolute and imaginary part of a complex electric field? What do they stand for?
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Can the magnetic lines of force of two or more magnets intersect each other?
Basic property of magnetic lines of force is that, they can never intersect each other. Among the two points given below, which one is correct?
Magnetic lines of force of same magnet can't intersect ...
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Electric Field inside a regular polygon with corner charges
If we have equal charges located at the corners of a regular polygon, then the electric field at its center is zero. Are there other points inside a polygon where the field vanishes?
The simplest ...
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Why is the conductor an equipotential surface in electrostatics?
Since the electric field inside a conductor is zero that means the potential is constant inside a conductor, which means the "inside" of a conductor is an equal potential region.
Why do books also ...
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Influence of charged particle's own electric field on itself
I read this in my textbook: A charged particle or object is not affected by its own electric field.
Since I find this completely unintuitive and my mind is yelling "wrong! wrong! how could a particle ...
user20250
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Is force due to electric field instantaneous? If not then why?
Suppose a charge $q$ is experiencing a force due to charge $Q$. Suppose we move the charge $Q$ very slowly (no acceleration) what's the instantaneous impact on the charge $q$? How will the $q$ react?
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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 be discontinuous?
"This is because of abrupt discontinuity of fields"
I have read this or similar sentences in many papers. I am bit puzzled. How and under what conditions electric field can be discontinous? ...
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How is energy stored in magnetic and electric fields?
We say that there is energy associated with electric and magnetic fields. For example, in the case of an inductor, we give a vague answer saying that an energy of $\frac{1}{2} LI^2$ is stored in the ...
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Meaning of the Poynting vector
In a book I am studying, the Poynting vector is defined as:
$$ \mathcal{P} = \mathbb{E} \times\mathbb{H} $$
and it is described the Poynting's theorem, that states that the flux through a surface ...
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What happens if you use a battery to charge up a capacitor fully, and then disconnect the battery, where does the charge 'go'?
The title says it all really, but I think that since the battery is disconnected there is now an 'open circuit'. I know that charge can only flow if the circuit is complete (closed).
But the part that ...
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