Questions tagged [dipole]
The dipole tag has no usage guidance.
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How does an antenna work?
I'm looking for a model of an antenna that would explain how it works an in particular where the values of impedance like 36.5 ohms come from. I've tried looking but everything i found was overly ...
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Why does an oscillating charge emulate an oscillating dipole in the far field limit?
I understand Thomson scattering as: When an EM wave is incident upon a charge causes it to oscillate in turn releasing energy as another electromagnetic wave.
In an Electrodynamics lecture we took a ...
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Energy of electric dipole near a conducting plate [closed]
How to find the energy of the dipole when put near a conducting plate at distance $a$ with angle $\theta$ from the normal vector to the plate? I used the method of images and the formula $U=-\vec{E'}\...
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Dipole Antenna: Electromagnetic Wave
I have read about wave propagation and dipole antennas here. I do not understand how a single electromagnetic wave (i.e. the electric field in particular - I can come up with the magnetic field later) ...
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Modeling a pure dipole as a function similar to a Dirac delta function
I am taking an undergraduate course in E&M following Griffiths.
I was wondering if there is a good way to embed the information of a dipole into the charge distribution (and if it would be of any ...
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Energy conservation in dipole capacitor interactions
If we bring a separable dipole (say a single ammonium chloride molecule) from infinity to the center of a capacitor, once the dipole stabilizes and the rotational energy is lost to electromagnetic ...
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Wave Propagation: Dipole Antenna
I was watching the following video here. This video explains the following image below represents an electric field generated from a dipole antenna. How does a single wave of electromagnetic radiation ...
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Hertzian Dipole: Why is there no longer a phase shift at $\frac\lambda2$? [closed]
Today we learned about the Hertzian Dipole. Out teacher told us that the length of the wire connecting the two capacitor plates is $l=\frac\lambda2$. He also stated that there is a no more phase shift ...
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Attractive or repulsive force between two statically charges plates [duplicate]
So I'm trying to calculate some mechanics for an electrostatic attraction/repulsion system and I want to make sure that I'm using the correct numbers. I did a bunch of research on my own and I think I ...
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Derivation for Quantum optics dipole radiation formula
An often used formula for the radiation field of a dipole is the following one:
\begin{align}
\vec{E}(t, \vec{x}) = \frac{1}{4 \pi x^3} ( 3 \hat{x} [ \hat{x} \vec{d}(t_r)] - \vec{d}(t_r) ) + \frac{1}{...
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Problem on Griffiths: Finding potential [closed]
For this problem, I understand that I have to use separation of variables to do this question. However, I was confused by the boundary condition in the solution.
Shouldn't the boundary condition be $\...
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What is the interpretation of the matrix elements of a second order perturbation capturing dipole-dipole interactions between two molecules?
The system I am studying is one molecule comes in close proximity with another molecule, and we are interested in calculating the energy of the resulting induced dipole-dipole interactions. I want to ...
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$\vec{E}$-field in toroidal polarized dielectric
In an electrostatic situation, imagine a dielectric torus that is permanently polarized with polarization given by:
$\vec{P} = P(r, z) \hat{\phi}$
(Here cylindrical coordinates are used with the $z$-...
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Different derivations of dieletric polarization charges in Griffiths and Feynman
I am reading Griffiths's Introduction to Electrodynamics (3rd edition). In the part of dieletric polarization (p.166), the author first adopts the potential for a single dipole:
$$V(\mathbf r)=\frac{1}...
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Meaning of electric dipole moment
what is the meaning of electric dipole moment?
Or why do we need to define electric dipole moment?
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Multipole expansion, same charges
I know dipole is defined with 2 opposite charges. That's why in EM dipoles exist, while in gravity they do not.
However, I view multipole expansion as a way to describe how the distribution of charges ...
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Understanding polarization and magnetization intuitively?
I am trying to develop a more intuitive understanding of the field produced by magnetization and polarization.
I have the following image, and I can derive it from Maxwell's equations what the fields ...
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Computation of the Force acting on an electric dipole [closed]
I’m having trouble computing the force on an electric dipole. I will simplify the problem so that I can only post the problematic part. There is a point charge $q$ at the origin of our Cartesian ...
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Dipole approximation
I am studying the "dipole approximation" as is defined in quantum optics. (See, for example Introductory Quantum Optics by Gerry and Knight, pages 24–25.) In this situation, we have the ...
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Why do the nucleons interact via strong force even though they are color neutral?
Particles that transform non-trivially under color $SU(3)$ interact via strong nuclear force. However, neutrons and protons, despite being color singlets, interact via the strong force. How do we ...
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What does centre of mass of charge mean?
I am unable to understand what does this centre of mass of positive charge and centre of mass of negative charge mean??
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What does centre of positive and negative charge separated by a small distance mean? [duplicate]
I dont understand the meaning of this statement that centre of positive and negative charge is separated by a small distance??
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In Maxwell's equations concerning dielectric materials , does the electric field represent the external electric field or the net electric field?
Let's assume we have dielectric material and we apply an external electric field that acts on it (let's call it Ex ) . As a resault we get dipoles who in turn create another electric field (let's call ...
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Deriving dipolar coupling in spherical coordinates
I am trying to get to the well-known expression of the tensorial coupling between two dipolar quantities, written as an interaction between two centers $\vec{r}$ and $\vec{r}'$ using their distance $d=...
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Why do we make a dipole a ideal dipole?
My question is that why do we make a dipole a ideal dipole ($q\to\infty$ and
$d\to 0$) …i mean i want the reason behind to take this and what is the problem of taking a charge with some magnitude (not ...
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Density of current in a Elementary Dipole
I can't understand this formula from my textbook, I'm trying to understand why the Density of Current is I*ΔZ(ΔZ is the lenght of the dipole) i mean a density of current would be I/Δs (with Δs the ...
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Point dipole approximation limit
Can I approximate the field of a 10 mm length x 5 mm radius cylindrical magnet at 8 mm away using a point dipole approximation?
I was wondering if it would still be possible to create a semi-accurate ...
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Schrödinger equation compared to Gauss law for electrostatic polarization?
Consider an electrically neutral isolated metallic sphere in vacuum. Suppose we approach this sphere with a negative point charge. When the point charge is close enough, the electronic density on the ...
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Do we experimentally know how a magnet reacts in a curling / non-zero-curl magnetic field?
There are two possible formulas for the magnetic force on a magnetic dipole moment due to the inhomogeneity of the magnetic field:
$$ \vec{F}_{A} = \nabla (\vec{m}\cdot\vec{B}) \qquad\text{ and }\...
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Potential energy of an (electric) dipole is said to be zero when the angle it makes with the applied uniform field is zero yet it experiences torque
My doubt is that I am unable to understand why a dipole would continue to experience a torque due to a field eventhough the potential energy is zero for angle 90⁰ it makes with the field.Like,there is ...
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Does this basic example of two bar magnets preserve angular momentum conservation?
Let's say I hold two bar magnets side by side both vertically aligned ($z$-axis). I don't want to worry about their shapes, so let's approximate them as dipoles. I will use the dipole formula rather ...
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Why equipotential surface for an electric dipole is concentric oval shells around the opposite charges?
Why equipotential surface for an electric dipole is concentric oval shells around the opposite charges? Please explain.
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Electric Field Lines - Why do we draw such lines for dipole?
In a dipole case (1 proton / 1 electron), we draw $E$ field lines such as they go and move into the negative charge. If we take an example point near negative charge's upside vertically, we see there ...
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Why is the magnetic field due to a dipole at equatorial position opposite to the magnetic moment?
I understand that the direction of the magnetic field lines at the equatorial plane is opposite to the direction of the magnetic moment by definition. Is there a reason of physical significance as to ...
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Why in an isotropic, linear and homogeneous dielectric, the average electric moment can be expanded as a series of electric field $\mathbf{E}$? [duplicate]
As I was reading this classic 1939 document by Kirkwood The Dielectric Polarization of Polar Liquids. It is stated in the text that the average electric moment in an isotropic liquid can be expanded ...
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How does a positive charge's electric field lines loop back to negative charge?
In this video about electric dipoles, at 6:14, the speaker mentions that all of the red lines will loop back into negative (blue) charge, but I don't see how this is possible. Specifically, he gives ...
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What's the relative phase between current, voltage and electric field in a receiving dipole antenna?
To help keep the question simple, please assume a half wavelength dipole at resonance such as in the image below:
I have been thinking about this problem using the analogy of a harmonic oscillator: ...
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Oscillating dipole, longitudinal Electric field oscillation?
Assuming the presence of a dipole consisting of two oscillating point-like charged particles on the z axis. Lets say whose motion follows $q_{\pm}=\pm 1\pm \frac{1}{2}\cos(\omega t)$, it is a well ...
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How and why potential energy is stored in a dipole in uniform electric field?
I learnt that potential energy is stored in a dipole in uniform electric field when it is rotated from theta = pi/2 to any other theta, and the magnitude of stored potential energy can be found out by ...
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The force on a magnetic dipole in a non-uniform magnetic field
Let's say there is a non-uniform magnetic field $B=(0,0,z)$ (i.e. the field is parallel to $z$-axis and the amplitude is linearly changing along $z$-axis). If there is a current loop (=magnetic dipole)...
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Is potential enough to determine dipole distribution?
I was working on a problem and I had to mathematically distinguish a charge and its distribution from a dipole and its distribution in the space. Following is an example where I am confused how to ...
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Issue in justifying the use of dipole potential in the calculation of bound charges in a dielectric
We have a polarised material, suppose. The goal, is to find the bound charges.
DJ Griffiths (4th ed, section 2.1, page 173) "chops" the material into smaller infinitesimal chunks and writes:
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How is a dipole stable?
So I was reading about dipoles, two charged particles of opposite charges a very small distance from each other. But if the particles have opposite charges, shouldn't they attract and crash into each ...
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Electric field of dipole antenna
I have seen that the electric field of a dipole antenna detaches and propagates.
For a section of the detached electric field, will the antenna experience recoil if the detached field moves a charged ...
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How do I renconcile electric potential and field of a dipole along its perpendicular bisector?
It's been a while since I've studied electrostatics and is my first time posting here, so please forgive me if I'm missing something basic.
According to my reference book, the electric potential of a ...
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Classical dipole-dipole interaction in iron
I've been reading about the classical magnetic dipole-dipole interaction and I'm wondering how it would work in a ferromagnet element like iron (theoretically under the assumptions I will write below)....
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Optical matrix element in graphene: is electron $k$ perpendicular to $E$?
I faced some problems with understanding the process of light absorption in 2D (e.g. graphene). Suppose we have Dirac graphene hamiltonian, skipping all numerical factors:
$$ H = \hbar v\begin{pmatrix}...
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What is the secret behind the striking similarity between a quark pair and a bar magnet?
If one tries to split a pair of quark and an anti quark, one ends up with two pairs, in the same way, when one tries to break a magnet in half, one end up in the same way with two magnets, so is this ...
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Dipole Moment of a Homogenously charged cylinder [closed]
A Homogenously charged cylinder of length L with Radius R and charged Q is presented. I am asked to find the dipole moment, the charge density is not given and only this Q value is given. I know the ...
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How does Dipole coupling affect macroscopic polarizability and refractive index
I have taken some measurements of refractive index (refractometer (commercial Brix meter), nD20 i.e. 20 degrees C and 589 nm) and density of sucrose/water mixtures and also of ethanol/water mixtures.
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