Questions tagged [dipole]

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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 ...
Jan Szwyngel's user avatar
1 vote
2 answers
29 views

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 ...
Nicojwn's user avatar
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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'}\...
Krum Kutsarov's user avatar
2 votes
4 answers
94 views

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) ...
William Garske's user avatar
4 votes
1 answer
694 views

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 ...
Pallav Pant's user avatar
1 vote
1 answer
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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 ...
Pranshu Nemani's user avatar
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1 answer
66 views

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 ...
William Garske's user avatar
1 vote
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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 ...
Janek's user avatar
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1 answer
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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 ...
ADesilets's user avatar
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0 answers
34 views

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}{...
Quantumwhisp's user avatar
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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 $\...
Irene's user avatar
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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 ...
McKinley's user avatar
1 vote
2 answers
55 views

$\vec{E}$-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 $z$-...
Lugerfan's user avatar
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1 answer
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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}...
rioiong's user avatar
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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?
Physics Ed's user avatar
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1 answer
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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 ...
Matteo's user avatar
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1 answer
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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 ...
reesespieces's user avatar
1 vote
1 answer
43 views

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 ...
Claudio Menchinelli's user avatar
3 votes
2 answers
350 views

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 ...
Julio Abraham Mendoza Fierro's user avatar
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2 answers
98 views

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 ...
Solidification's user avatar
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1 answer
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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??
Physics student's user avatar
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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??
Physics student's user avatar
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2 answers
66 views

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 ...
firas's user avatar
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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=...
Szgoger's user avatar
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1 vote
4 answers
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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 ...
Physics student's user avatar
0 votes
1 answer
46 views

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 ...
Martino Pistis's user avatar
0 votes
1 answer
73 views

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 ...
ggggggggg's user avatar
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0 answers
57 views

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 ...
YoussefMabrouk's user avatar
1 vote
0 answers
46 views

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 }\...
Maximal Ideal's user avatar
3 votes
3 answers
125 views

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 ...
Scientist 's user avatar
0 votes
1 answer
63 views

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 ...
Maximal Ideal's user avatar
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3 answers
145 views

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.
Sukriti Sharma's user avatar
0 votes
1 answer
55 views

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 ...
Matt's user avatar
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0 answers
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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 ...
Anjana Asok's user avatar
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0 answers
19 views

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 ...
Zhao Dazhuang's user avatar
0 votes
1 answer
93 views

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 ...
Giorgi Lagidze's user avatar
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0 answers
59 views

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: ...
Christian's user avatar
0 votes
1 answer
43 views

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 ...
pip's user avatar
  • 23
0 votes
1 answer
81 views

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 ...
Rohan Singh's user avatar
2 votes
1 answer
173 views

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)...
EugeneB's user avatar
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0 votes
1 answer
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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 ...
Mahammad Yusifov's user avatar
2 votes
1 answer
125 views

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: ...
nickbros123's user avatar
4 votes
2 answers
124 views

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 ...
Nikunj Mundhra's user avatar
2 votes
1 answer
142 views

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 ...
Simon Lin's user avatar
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0 votes
3 answers
101 views

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 ...
Swik's user avatar
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0 votes
1 answer
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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)....
user9867's user avatar
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0 answers
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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}...
goroshek's user avatar
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3 votes
1 answer
64 views

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 ...
Jack's user avatar
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1 vote
0 answers
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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 ...
Mark Kavanagh's user avatar
1 vote
0 answers
64 views

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. ...
W_vH's user avatar
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