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Questions tagged [dipole]

Use this tag for questions regarding electric or magnetic dipoles, meaning a field on an object with a north and south pole or two point charges of equal magnitude.

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Dipole term in light-matter interaction

I have a question regarding the description of the term “dipole” in light-matter interactions. If I understand it correctly, there are 3 different things that one can declare as a dipole during light-...
Python_Coder's user avatar
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42 views

Dipole antennas and the $B$ field

A dipole antenna responds to the electric component of a EM wave. Does the magnetic component of a EM wave have any effect on the performance of a receiving dipole antenna?
Rich D's user avatar
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How to go from a vector operator to its components?

(I'm sorry if this question is a duplicate, I couldn't find anything that answered my question.) I'm doing an exercise where I'm supposed to get the matrix elements for the vector operator $D$ (the ...
Hector Freire's user avatar
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Linear approximation of the magnetic dipole field

Summary: using 3 angles to represent a magnetic dipole's orientation is redundant because the rotation around the $z$-axis of the dipole does not change the magnetic field, there are only 2 DOFs for ...
William Lin's user avatar
1 vote
0 answers
23 views

Can we relate the dipole force on a two level atom to the AC stark shift it experiences?

Consider a two level atom, with ground state $|g\rangle$ and excited state $|e\rangle$. In the rotating frame, the dynamics of the two level atom interacting with radiation detuned by $\Delta$, and ...
Adrien Amour's user avatar
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Orientation of Magnetic Induction of a Dipole Source in MEG

I am working with source-reconstructed MEG data, and what I would like to know is that when we obtain the magnetic induction (using the right-hand thumb rule) of a dipole source, is it only the ...
neurysh's user avatar
2 votes
2 answers
226 views

Dipoles as vectors

A triatomic molecule $X_2Y$ has plane structure as shown in figure. Due to difference in electronegativity, charge acquired by each X atom is $q$ and charge on Y atom is $- 2q$. The bond length ...
Anshu Gupta's user avatar
1 vote
2 answers
66 views

Potential of an electric dipole

I'm currently working my way through Griffith's Introduction to Electrodynamics (4th ed). In chapter 3 section 4, he shows that we can take the equation for the electric potential of a continuous ...
ReggiePlasmaQs's user avatar
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1 answer
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Dipole moment in an electric system when the charges are not symmetrically distributed

Suppose we have two -q charges and +2q charge ate the corners of an equilateral triangle. Now to calculate the dipole moment suppose we assume that the +2q charge is 2 charges of +q magnitude. My ...
Pushkar Kumar's user avatar
1 vote
2 answers
96 views

Electromagnetic field of dipole antenna

Why do dipole antennas generate EM waves by alternating electric fields instead of alternating magnetic fields? Why don't alternating magnetic poles detach the magnetic field like how it can do so ...
Simon Lin's user avatar
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1 vote
2 answers
52 views

Minimum frequency for a dipole antenna to work

Does a dipole antenna need a minimum frequency of AC to make the electric field detach and propagate?
Simon Lin's user avatar
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2 votes
2 answers
378 views

Dielectric and dipole

When a molecule of a dielectric material is placed in an electric field, the molecule acquires an electric dipole moment. Why?
Sam Tunkaho's user avatar
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Equation relating the current carried by a solenoid to the force experienced by a magnetic dipole?

I am trying to find an equation or a series of equations that relates the current I carried by a solenoid of length L with turns N to the force F experienced by a magnetic dipole of strength M that ...
cyalatergator's user avatar
5 votes
1 answer
43 views

Entropy of dielectric in Capacitor?

So I am learning about dielectrics, and my professor was saying that if we connect capacitor containing dielectric to a DC source, theoretically it should produce little to no heat (the only heat ...
Kshitij Kumar's user avatar
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0 answers
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Time average of product of 2 function with same frequency

Hi I'm Reading a notebook on "light atom interactions" There is this calculation I don't understand of average power - $$P=\overline{-\boldsymbol{E} \cdot \frac{\mathrm{d} D}{\mathrm{~d} t}}=...
Yarden Sharabi's user avatar
2 votes
0 answers
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Do neutral atoms have an electric field? [duplicate]

The charge of an atom is the sum of its nuclear charges (protons and electrons). If a atom is neutral, does it mean it does not have an net electric field? I thought about this a lot, here is some of ...
Kryptic Coconut's user avatar
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1 answer
68 views

What's the Lagrangian of an electric dipole in an external electric field?

I took electromagnetism a while ago, but now that I took Lagrangian and Hamiltonian mechanics, this question came up to me when I imagined an electric dipole in the presence of a uniform electric ...
Alf20's user avatar
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Sakurai's explanation of the dipole approximation

In chapter 5 of Sakurai's Modern Quantum Mechanics (3ed), he considers the dipole approximation for an electron absorbing electromagnetic radiation due to a harmonic electromagnetic potential. In the ...
Silly Goose's user avatar
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How did the scientist measure the dielectric constant? Does the dielectric constant relate to an alignment with the electric field?

I heard that the dielectric constant of water is around 78. When we think about the way we get the $\kappa$ of water, Can we get the $\kappa_{water}$ by putting the water molecules on the $\vec{E}_{...
J.H's user avatar
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-1 votes
3 answers
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Why can't the two charges in an electric dipole exist independently in an uniform electric field?

Why can't the two charges in an electric dipole exist independently in an uniform electric field? What I mean is, why should they behave as if they are connected together by a rod between them? What ...
Vinay5101's user avatar
1 vote
1 answer
64 views

Vector Magnetic Potential and pointwise current density source

I am currently studying antennas and I am trying to understand how to solve the following vector equation $$\nabla^2A+k^2A=-\mu J$$ in the case when there is a point current source at the origin. The ...
edoverg's user avatar
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1 answer
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Electromagnetic Dipole Radiation Derivation

I was reading this wikepedia page, about the dipole radiation, and I was wondering how to derive the $\mathbf E$ and $\mathbf B$ fields in this situation. I've started using the retarded potentials: $$...
Álvaro Rodrigo's user avatar
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1 answer
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Coexistence of a static electric and magnetic dipole

I have been trying to construct a charged object (not a conductor carrying any current) that can behave simultaneously as an electric and magnetic dipole and then calculate the electric and magnetic ...
Cognoscenti's user avatar
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0 answers
46 views

Decay rates, time-energy uncertainty, and photon spectrum in two-level system

This question concerns mainly a few statements from the following article https://journals.aps.org/pra/abstract/10.1103/PhysRevA.94.063839. It states: "Early studies of two-level quantum systems ...
AlienTek's user avatar
1 vote
1 answer
96 views

Potential energy of an electric dipole without any external field

What is potential energy of an electric dipole without any external field? If its 0 then why? Wouldn't the charges get attracted thus do work so they must have some potential energy.
SHINU_MADE's user avatar
1 vote
1 answer
116 views

Can static electricity (charged balloon) attract any liquid other than water?

I know that a charged balloon can attract a stream of water, because it is a dipole. I am wondering if a charged balloon can attract any other liquid other than water? Does it have to be a dipole? ...
Carbon's user avatar
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1 vote
0 answers
28 views

How can you understand curl of electric field illustratively?

Considering the curl of the electric field of an electric dipole, this will be zero in absence of magnetic effects which is clear to me. I watched a video by 3Blue1Brown (some time ago) who explained ...
Rasmus Andersen's user avatar
1 vote
1 answer
57 views

A question about dipole approximation

While reading Chapter 5 in [1], I became confused with the dipole approximation and the $\bf{r}\cdot \bf{E}$ Hamiltonian. The total Hamiltonian is given by $H=H_0+H_1$, where $H_1=-e\bf{r}\cdot\bf{E}(\...
Du Xin's user avatar
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1 vote
1 answer
92 views

Interpretation of the terms in classical hamiltonian of a charged particle in a magnetic field

For a particle of charge $q$ in a homogeneous magnetic field along $z$-axis, $\vec{B}=B\hat{z}$, its classical Hamiltonian is given by $$H=\frac{(\vec{p}-q\vec{A})^2}{2m}.$$ In the gauge $\vec{A}=\...
Solidification's user avatar
-1 votes
1 answer
93 views

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
65 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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2 votes
4 answers
166 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
734 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
28 views

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
0 votes
1 answer
149 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
0 answers
37 views

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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0 votes
1 answer
119 views

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
0 votes
0 answers
49 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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0 votes
0 answers
36 views

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
70 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
0 votes
1 answer
50 views

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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0 votes
1 answer
36 views

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
0 votes
1 answer
78 views

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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2 votes
1 answer
103 views

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
61 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's user avatar
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3 votes
2 answers
660 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
0 votes
2 answers
112 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
1 vote
1 answer
70 views

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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0 answers
37 views

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
0 votes
2 answers
98 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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