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Questions tagged [dipole]

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Dipole over a conductor plane

If we place a charge $q$ over an infinite grounded plane we can find the potential in all points of space using the method of images and find the induced surface charge on the plane. However, how ...
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0answers
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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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3answers
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Is it necessary that, in $q$ dipole charges should be equal and opposite?

When I read about multipole expansion in Griffith book, i saw that "if total charge is zero, dipole moment is independent of origin." I have some doubts about this. I learned that the dipoles are two ...
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1answer
56 views

Torque on dipole in a non-uniform electric field [duplicate]

What happens when an electric dipole is kept in a nonuniform electric field?
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1answer
55 views

Radial vs tangential component of electrical field due to dipole

I was wondering that why should the maximum magnitude (with respect to $\theta$) of radial component of electrical field of an electric dipole, $$E_r=-\partial V/\partial r=\frac{2p \cos\theta}{4\pi\...
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1answer
34 views

Electric field of two equal charges of the same sign [closed]

Two equal positive charges are at distance d, -d from the origin on the y axis. What is the distance on the x axis beyond which a small perturbation in y will move a particle away from the x axis? ...
2
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1answer
50 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
32 views

How is total angular momentum conserved in electric dipole transitions for ΔJ = 0 in a multi-electron atom?

One of the selections rules is that ΔJ=0,±1 for an electric dipole transition in a multi-electron atom, where J is the total angular momentum. Since ...
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1answer
26 views

Electrodynamics confusion - Hertzian dipole

I am studying a course in Electrodynamics and we are just covering retarded potentials and the Hertzian dipole. In my lecture notes, we have calculated the magnetic vector potential $A$ in the ...
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0answers
46 views

Paradox in conservation of energy

Let us assume there is a constant electric field in an interested region (finite volume)and a non-conducting object is thrown into it with speed $v$ and now take the second scenario with the same ...
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3answers
30 views

Deriving the electric displacement field ($D$ field)

I am trying to derive the $D$ field (or electric displacement field): $$D=\varepsilon _{0}E+P$$ I am using the following relationships: $$\rho=\rho_{f} + \rho_{b}$$ $$ \rho_{b} =-\nabla \cdot P$$ ...
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1answer
127 views

Question on force between dipoles [closed]

Two point dipoles of dipole moment $p_1$ and $p_2$ are at a distance $x$ from each other, and $p_1$ is parallel to $p_2$. The force between the dipoles is? I’m not understanding what does point ...
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3answers
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Isn't magnetism governed by the inverse square law? [duplicate]

Why does magnetism appear to decay much faster than gravity with distance? A clear indication of this is the fact that a magnet that in short distance able to overcome gravity and pick up some object,...
3
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1answer
102 views

How to derive the $\frac{4\pi}{3}\vec{p}\delta^3(\vec{r})$ element for the dipole field, from its potential?

This might be a bit more general question about how to figure out what is the appropriate (delta) expression in singular points, but e.g. for the dipole, we can derive its potential by a taylor ...
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0answers
24 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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2answers
92 views

What is the physical significance of Dipole moment?

What does dipole moment physically signify? I know it is the product of 2 charges and distance between them. Like momentum is the product of mass and velocity, but physically it shows the quantity of ...
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1answer
44 views

Why does a ionic crystal polarize more at low frequencies rather than at high ones?

And if there was a difference if the propagational mode of the electric field in the crystal is longitudinal or transverse.
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2answers
46 views

Working principle of an optical stretcher

I understand that while using an optical stretcher experimental apparatus we attach a small dielectric ball to the specimen of study which can either be a DNA molecule, a Biological cell or any ...
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1answer
45 views

Question about Optical tweezers working principle

Why do particles on the periphery of the laser beam in optical tweezers apparatus drift to the center of the beam? What force pattern causes this pull to the center?
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1answer
29 views

What is the mechanism by which light induce polarity in tiny particles?

I understand that the electric field in light induces polarity in tiny microparticles for example. Can someone explain the mechanism of how the vibrating electric field in light induces a dipole ...
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2answers
153 views

Expression for electric potential around an electric dipole in Cartesian coordinates

I'm trying to find the equation of the electric potential of a electric dipole in Cartesian coordinates. The equation should take the form of something looks like this: $$z = x\exp(-x^2-y^2)$$ ...
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2answers
316 views

How to calculate the dipole potential in spherical coordinates

I want to calculate the dipole potential in spherical coordinates. I know that the potential can be calculated with $$ \phi = - \int \mathbf E \cdot\mathrm d\mathbf r,$$ but I don't know the electric ...
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0answers
31 views

Is a dipole vector directly dependent of the dielectric constant in vacuum?

Supposing to have a little gas particle of diameter d surrounded by an electric field that varies sinusoidally in time $\vec{E} = \vec{E_0}sin(\omega t)$ such that $d << \lambda $, I want to use ...
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1answer
24 views

Does half wave in dipole means that duration of 1/4 of signal cycle should equals capacitor charging time, if we consider that dipole is capacitor?

Does half wave in dipole means that duration of 1/4 of a one signal cycle should equals capacitor charging duration, if we consider that dipole is a capacitor?
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electric dipole spin resonance and anomalous coordinate

On the wikipedia page about electric dipole spin resonance (EDSR), they define what they call 'the anomalous coordinate,' which is $ \textbf{r}_{so} \approx \frac{\hbar^2 |g|k}{m_0 E_G}$. Apparently, ...
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3answers
282 views

Electric dipole moment when charges are not symmetrically opposite each other [closed]

In the above figure, I want to calculate the net dipole moment. I know that dipole moment is a collection of equal and opposite charges. But, according to that concept, the above figure cannot be a ...
1
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1answer
26 views

From where energy comes for the heat released when direction of electric field is changed with a dipole placed in the field

This is an example problem in my book. Forget about the values. Initial anf final(after heat is released) conditions in this problem are same, ie, dipole moment and electric field are in same ...
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1answer
390 views

Electric dipole moment of electron: about what point is the moment taken?

There is a lot of experimental research activity into whether the electron has an electric dipole moment. The electron, however, has a net charge, and so its dipole moment $$ {\bf \mu}= \int ({\...
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4answers
448 views

Why does an atom in an oscillating electric field behave like an electric dipole?

How can I understand that an atom subjected to an oscillating electric field (e.g., $\vec{E}=\hat{i} E_0\cos\omega t$) behaves like an oscillating electric dipole? What is the underlying picture that ...
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4answers
57 views

Analogue of charge distribution in magnetostatics

Short of magnetic monopoles, what is the analogue of charge distribution in magnetostatics? Can we call it magnetic pole distribution?
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0answers
110 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 $P$ ...
3
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1answer
56 views

When can we consider dipoles?

A dipole is a collection of two oppositely charged particles held at some distance, but if two charges are unequally charged (but oppositely charged) how do we take the dipole between them? Do we only ...
1
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1answer
119 views

What is the difference between the dipole in IR and Raman vibrations?

In order for a vibration to be IR active, there must be a change in the dipole moment ($\mu$) of the molecule, which is given by: $\mu$ = $\sum$ q * r Where q is the charge magnitude and r is the ...
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0answers
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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
65 views

Resolution of dipole moment into components [closed]

In the derivation that involves finding the electric field due to a dipole at a general point on a plane in which the dipole lies, the following procedure is followed: Resolve the dipole moment into ...
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1answer
70 views

Why is the potential energy of spring negative while it's positive for a dipole?

Potential Energy is the work done against the conservative force As the definition suggests , for a spring $$ U= -\int F \cdot \mathrm{d}x \,.$$ But for a dipole placed in an electric field $$ U= \...
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1answer
57 views

How can the magnetic field of a dipole be extremely large close to its singularity?

I am trying to figure out the magnetic field close to a micrometer sized bar magnet in my experiment. The field gets detected 1 micrometer away from the north of the bar magnet. For now, I just take ...
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0answers
16 views

electric dipole moment, multipolar developement

There is a note in my lecture : You have the total electric charge, equal to $ \frac{q}{4 \pi \epsilon_0 r} $ the electric dipole moment, equal to $ \frac{ \bf{p} \cdot \bf{u_r} }{4 \pi \epsilon_0 r^...
3
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1answer
95 views

Is a dipole fusion reactor feasible?

It is well known that the earth's dipole-like magnetic field is able to confine charged particles to paths that spiral along the field lines. That's why we have auroras and the Van Allen radiation ...
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1answer
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Function of dipoles in particle accelerators

I know now that quadrupoles are used to focus the beam in a particle accelerator, but what about dipoles? Are they used to center or accelerate the beam? The number for the LHC magnets I think it is ...
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1answer
77 views

Electric field due to a short dipole at a point $A$ on the axis

There is a short dipole $ X,Y$ of charge $+q$ and $-q$ placed along the x-axis and then we consider the point at $A$ which is far away from the dipole and lies on the x-axis. The electric field $E_\...
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0answers
34 views

What is a force multipole?

In a recent talk about physics and mechanics inside the cell, I heard such terms as 'force monopole' and 'force dipole'. What do such terms mean? Are they talking about the angular distributions, ...
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0answers
37 views

Tight binding model with dipole momentum

I'm repeating a paper(Dirac Semimetals in Two Dimensions): arxiv.org/abs/1504.07977 However, I'm in trouble with case 4: This is a two-site squre lattice model. Meanwhile, we displace the B site in ...
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1answer
447 views

How would we calculate the dipole moment of a charge combination (of 3 or more charges) whose magnitudes are different but net charge is zero?

How would we calculate the dipole moment of a charge combination (of 3 or more charges) whose magnitudes are different but net charge is zero? As a special case, what if the net charge is not zero? ...
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1answer
1k views

Do neutrons exhibit momentary small charges due to the movement of its quarks?

So in a similar way to electrons moving in atoms, causing induced dipole-dipole interactions, can neutrons momentarily attract or repel?
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1answer
250 views

How do I graph a magnetic field?

For a school project, I'm trying to graph a magnetic field. I found this page on the NASA website with spherical coordinate equations for a dipole field, but I'm having trouble interpreting the page. ...
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0answers
98 views

Electric dipole - ion interaction energy

The following is a derivation for the expression for the interaction energy of an electric dipole with the electric field from an ion When i tried another derivation, this time starting from the ...
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0answers
51 views

Electric Field of Dipole..found by superposition?

I am working on a problem where I look for the electric field caused by an electric dipole. I can easily find it by taking the negative gradient of it's potential, resulting in $$E = \frac{P \ cos(\...
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2answers
419 views

Does an accelerating electric dipole radiate?

For such a simple question I'm finding it remarkably hard to get a definitive answer. Googling has not helped me. Consider an ideal electric dipole that is constant i.e. neither its magnitude nor ...
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2answers
135 views

Why does the electric field strength for a dipole go as $1/r^3$?

I've been given the following graphic to help wrap my head around this. If the potential can be shown to represent a $1/r^2$ relation, then I'm more than happy to accept that the electric field is ...