Questions tagged [dipole]

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How do electric dipoles exist?

Ok, this might seem like a trivial question, but how exactly does an electric dipole exist, since positive and negative charges attract each other on the basis of Coulomb's law? Adding to this, I ...
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3answers
395 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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1answer
180 views

What happens to the incident electromagnetic wave in Rayleigh scattering?

In Rayleigh scattering an incident EM wave causes an induced dipole oscillation of an atom/molecule, which in turn causes radiation at the same frequency of the incident wave. But what happens to the ...
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0answers
27 views

Energy of dipole using the electrostatic energy of all of space

I was watching my online lecs, and we were considering the electrostatic energy of a dipole. First, doing the torque-in-uniform-field calculations, and derived that $U_{rot}= - \vec{p} \cdot \vec{E}$. ...
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1answer
297 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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0answers
39 views

Is there a code for Ewald Summation for Dipoles?

Does anybody know if there exists a code that calculates the potential energy for a system with both point charges and point dipoles using Ewald summation? This would be a great help to my Master ...
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1answer
39 views

Questions on Forces involved in oscillating mass dipole

Say we have two balls of radius $R$ on both sides of a massless dielectric rod and it starts oscillating due to an external electric field. Other than the external field would there be an electric ...
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1answer
405 views

Electric current dipole moment

Electrical Current Dipole of dipole moment $\mathbf{p_{EC}}$ has unit of $A\cdot m$. My knowledge of dipole moments unfortunately stopped in high school where I learned that dipole moment $\mathbf{p}$ ...
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0answers
51 views

Integrand discontinuity of surface integral of electric field of dielectrics

I am reading an article here on dielectrics Equation $(4.10)$ is: $$\Phi(\mathbf{r})=\dfrac{1}{4\pi \epsilon_0}\int_{V} \dfrac{d^3r'}{|\mathbf{r}-\mathbf{r'}|} [\rho (\mathbf{r'})\ -\nabla'.\mathbf{...
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1answer
67 views

Can I replace a multipole expansion by a combination of separate dipoles?

If I want to be able to model a magnetic field flux density $\mathbf{B}$ from a magnetic source located at the origin at a position $\mathbf{r}$, it is my understanding that I can represent $\mathbf{B}...
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0answers
262 views

Conformal transformation: electric field of dipole

In beautiful paper (open access) authors calculate analytically optical response of "kissing" nanowires. Authors use method of "conformal transformation". Firstly, authors consider dipole (dipole ...
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0answers
72 views

Connection: Work on dipole <-> optical absorption

If I consider a two-level system with a ground and an excited state, I can compute the instantaneous rate at which work is being done on the dipole $\mu(t)$ by an electric field $E(t)$: $\dot{W} = E(...
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145 views

Mie Scattering for spheres with constant dipole moment

I was wondering whether there exists a theory that describes Mie Scattering for spheres that have a constant dipole moment. Since there are theories that describe Mie scattering in the case of a ...
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1answer
35 views

Constellation of charges in a quadrupole

I’d like to know if any constelation of 4 charges is a quadrupole. I have a task where there are 2 positive and 2 negative charged particles in the corners of a rectangle. And this is a quadrupole. Is ...
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29 views

Field of an infinitely wide magnetic dipole

Students commonly wonder about the near-analogies between electricity & magnetism. One such: The field of an electric dipole in the limit of an infinitely wide plane tends to 0 outside the plane (...
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40 views

Gravitational Waves, Dipole Radiations and Momentum

I am trying to understand Gravitational Waves and and going through MTW's book. They state that there can be no dipole radiation because of the conservation of momentum but gravitational waves also ...
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40 views

Confusion over Gauss' law for an ideal electric dipole

To find the charge density of an ideal electric dipole centred at the origin, I can evaluate the divergence of $\vec{E}(\vec{x})$ which equates to evaluating the laplacian of the potential. Working ...
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45 views

Trajectory of magnetic dipole in a inhomogeneous magnetic field

Goal: I want to use Python to illustrate how a magnetic dipole with magnetic moment m2 moves in a non-homogeneous magnetic field in a 2D-Plane. This field is generated by another magnetic dipole with ...
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0answers
36 views

Energy of cubic dipole lattice

Consider a single dipole in a cubic box with periodic boundary conditions, or an infinite cubic lattice/grid of parallel dipoles. Is there a simple expression for the energy?
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0answers
20 views

Dipole source directivity function? (Acoustics)

I'm trying to model the propagation of a dipole source and I need to know what is the directivity function (i.e. the polar pattern function) which describes it. I've read in an article that a dipole ...
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0answers
31 views

Directionality of dipole radiation and spontaneous emission

I have a question on the directionality of the field radiated by an oscillating charge and the directionality of the spontaneous emission of say a two level atom. When I first started studying physics,...
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2answers
193 views

Theoretical value of electric dipole moment of a molecule

Consider a hydrogen chloride molecule (HCl). Let's assume that we're given the distance between hydrogen and chlorine nuclei $d=1.27 \times 10^{-30} \mbox{m}$. How to calculate electric dipole moment $...
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1answer
75 views

Minimal coupling to electric dipole form

When deriving the electric dipole form of the semiclassical hamiltonian from the minimal coupling form, we define a new state vector as: $$\psi_{old}=e^{i\textbf{A}\cdot\textbf{x}/\hbar}\psi_{new}=\...
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34 views

Definition of $H$-field with Magnetization

i am trying to understand the H-field more intuitively. My textbook defines the H-field as follows: $\vec{B} = \mu_0 (\vec{H}+\vec{M}) $, where $\vec{M}=\frac{\sum_i{p_i}}{V}$ is the magnetic dipole ...
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58 views

Dipole moment in a bulk crystal

When calculating the dipole moment in a crystal, there is always one term neglected. This neglection is never discussed and I do not understand it at all. Assuming the Bloch functions $\Psi_{n,\vec{k}...
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0answers
48 views

How a sphere can be assumed as dipole?

From the book introduction to electrodynamics by David Griffiths , fourth edition, page no 279, there is an example to find the magnetic field of uniformly magnetized sphere. It said the magnetic ...
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105 views

Why is electric dipole moment represented by “p”?

I recently came across a text where the electric dipole moment was represented as "d" instead of the more commonly used "p". The reason behind using "d" here is probably that "dipole moment" begins ...
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70 views

Optical tweezers : dipole force or radiative pressure?

Two types of forces are usually considered to describe light-matter interaction. On the one hand, the radiative pressure, which corresponds to absorption - spontaneous emission cycles, is proportional ...
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925 views

Why is the electric field of an axial quadrupole not the same as the electric field of two axial dipoles, at far distance?

An axial electric quadrupole, made of four inline charges $(+q, -q, -q, +q)$ with opposite charges a distance $a$ apart, and the two $-q$ charges adjacent, has an electric field at a remote point $P$ ...
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22 views

How do you find the 2nd order perturbed energy shift from the quantised dipole hamiltonian?

Without using the Rotating wave approximation how do you find the trapping potential $U(\mathbf r)$ experienced by an atom at position $\mathbf r$ for arbitrary laser frequencies? This can be done ...
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1answer
189 views

Far field horizontal polarization component of a dipole antenna

An infinitely thin dipole radiates an electromagnetic wave which in the far field is vertically polarized, with zero horizontally polarized component. I am trying to understand what happens when the ...
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0answers
35 views

How do we visualize magnetic dipole transitons?

I am studying the transitions between the Kramers doublet sublevels of the ground electronic state of a Co(II) molecular compound. I know that the transitions are magnetic dipole allowed transitions (...
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181 views

water dipole moment

I'm working my way through Halliday, Resnick, Walker's chapter on electric fields, and there is a solved sample problem (22-5, 8th ed.) about calculating the charge separation on a water molecule. ...
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114 views

finite version of perfect electric dipole

Is there a finite object whose charge distribution is a perfect dipole (only has a dipole moment) yet doesn't involve any infinities or discontinuities in the fields? And if there happens to be a ...
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0answers
53 views

Electric and magnetic dipole

How does an electric dipole and magnetic dipole physically realizable? By feeding a wire with current does that become a dipole?
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130 views

Semiconductors: question about electric dipole transition selection rules between and within bands

Here is roughly what I understand about selection rules for electron transitions in a semiconductor quantum well: If it's from conduction band to valence band, the rule is $\Delta n = 0$. If it's ...
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0answers
36 views

Determination of electromagnetic wave absorption by molecular vibration mode

In this physics.stackexchange answer, it is stated that the absorption of electromagnetic wave at a given wavelength by a molecule is determined by its vibration modes. What is the exact equation/...
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0answers
87 views

Is the minimum number singular points of a continuous vector field on a 2-dimensional sphere 1 or 2?

Let's look at a continuous vector field on a 2-dimensional sphere. Say the vector field representing the velocity of an infinitely thin layer of water on the sphere, or the direction of the Higgs ...
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1answer
117 views

Electrostatic polarization of an axially symmetric conductor

A single point charge at the origin induces charge onto a grounded Z-axis symmetric conductor. The induced charge is given in cylindrical coordinates as $\sigma(r, z)$ since the Z symmetry means there ...
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1answer
153 views

Knowing the force of attraction of two bar magnets what is the force between two surfaces made of the same material?

Two bar magnets with area $a$, in axis, at a distance of $d$ ($d$ is much biffer than $a$) attract each other with a force of $F$. What is the force between two infinite surfaces made of the same ...
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0answers
143 views

Why do “virtual states” in Raman spectroscopy have absorbance profiles distinct from either the ground or excited states of an absorbing material?

Do virtual states in Raman spectroscopy have distinct and observable dipoles that can interact with and/or induce dipoles in other molecules (over extremely short femtosecond timescales)? This notion ...
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1answer
88 views

Can electrons be electrically polarized, i.e., can they acquire an induced electric dipole moment?

A comment on a recent question raises an interesting point: Neutrons can have intrinsic electric dipole moments. Neutrons also have a nonzero electric polarizability, i.e., they acquire an induced ...
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Spin Transition operator

What interaction Hamiltonian operator should one use when we consider photon emission through change in spin states?
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40 views

Force on a magnetic dipole

How to deduce the force on a magnetic dipole given by $F = \nabla(m \cdot B)$ from the Lorentz force?
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1answer
26 views

Doubt in the interaction energy of the dipole in an electric field

Consider a dipole ($\vec{p}$) in an electric field ($\vec E$) making an angle $\theta$ with the field. We can see that $V_1-V_2=Ed\cos\theta$ In books, the derivation for the interaction energy of ...
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25 views

Electric dipole moment, formula derrivation

I want to derive the formula for the potential energy of an electric dipole $$ U = - \overrightarrow{p} \cdot \overrightarrow{E} $$ where $\overrightarrow{p}$ is the electric dipole moment and $\...
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1answer
33 views

Potential of a continuous charge distribution and it's dipole term

I've a charge distribution, whose potential will be given as $$\begin{aligned} V(\mathbf{r})=& \frac{1}{4 \pi \epsilon_{0}}\left[\frac{1}{r} \int \rho\left(\mathbf{r}^{\prime}\right) d \tau^{\...
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2answers
78 views

What is the diff in operational range underwater between a dipole trimmed to resonate @2.45GHz versus a dipole tuned to resonate using a pi network?

(Sorry about the use of "diff", but I needed the characters.) In air, a half-wave dipole can be physically trimmed to resonance and will radiate well. It can also be tuned using a pi network ...
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81 views

Understanding the physical interpretation of bound charges in a polarized material

I'm reading Section 4.2.2 of Griffiths' Introduction to Electrodynamics (Third Edition): "Physical Interpretation of Bound Charges". He explains where the bound "surface charge density&...
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How to interpret bound charges geometrically?

Conceptually, it makes sense to say that when there is an electric field along $E=E\hat{n}$, then given a polarization $P$, the amount that $P$ aligns with the electric field is simply the dot product ...