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.
Questions tagged [dipole]
565 questions
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votes
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Why there is no dipole gravitational wave?
I have read that "thanks to conservation of momentum" there is no dipole gravitational radiation.
I am confused about this, since I cannot see the difference with e.m. radiation.
Is this due to the non-existence of positive and negative…
Arnaldo Maccarone
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votes
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Why is dipole the simplest source in electrodynamics?
I see this sort of statement in many materials, for example this:
The smallest radiating unit is a dipole, an electromagnetic point source.
and this:
The simplest infinitesimal radiating element, called a Hertzian dipole…
However, none of them…
xzczd
- 487
20
votes
1 answer
In the Lennard-Jones potential, why does the attractive part (dispersion) have an $r^{-6}$ dependence?
The Lennard-Jones potential has the form:
$$U(r) = 4\epsilon\left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^{6} \right]$$
The (attractive) $r^{-6}$ term describes the dispersion force (attraction at long range). Why is the…
Andrew
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20
votes
2 answers
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 direction change with time. If we apply an…
John Rennie
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votes
1 answer
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
$$
{\bf \mu}= \int ({\bf r}- {\bf r}_0)\rho({\bf r}) \,d^3r
$$
depends…
mike stone
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17
votes
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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?
Joshua Farrell
- 327
16
votes
2 answers
Magnets arranged in a sphere
If I was to take a bunch of magnets and arrange them in a sphere (And keep them there with glue or plastic or something) so that the north pole faces the outside of the sphere and the south pole faces the inside, would the magnet have the same pole…
Tnelsond
- 171
15
votes
3 answers
Electromagnetic field energy "paradox"
The starting point is the energy density in electromagnetic fields:
$$ u = \frac{1}{2} \left( \epsilon_0 |\mathbf{E}|^2 + \frac{1}{\mu_0} |\mathbf{B}|^2 \right) \tag{1}$$
The "paradox" is if we use this to test whether it is lower energy for…
PPenguin
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14
votes
3 answers
Is there an electric field around neutral atoms?
Even if the atom is neutral (equal numbers of protons and electrons), the electrons and nucleus form an electrical dipole, so there is still an electric field around them, even though the total charge is zero. Is this reasoning correct? So, every…
Jp_
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votes
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(Special relativity) A tilted dipole composed of $+q$ and $-q$ point charges moves at a horizontal velocity. Will it rotate?
Two point charges $+q$ and $-q$ are connected with a rigid insulating stick:
This dipole moves at a velocity $v$ to the right. Therefore, the charges should exert a magnetic Lorentz force $F_B$ on each other, causing the dipole to rotate.
On the…
isend
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13
votes
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Why is there a factor of 1/2 in the interaction energy of an induced dipole with the field that induces it?
In this paper, there's the following sentence:
...and the factor 1/2 takes into account that the dipole moment is an induced, not a permanent one.
Without any further explanation. I looked through Griffiths' electrodynamics to see if this was a…
llama
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13
votes
5 answers
What is the physical sense of the transition dipole moment?
So if the states are the same we achieve the expectation value of the dipole moment for a given state. I mean
$ \langle \mathbf{\mu} \rangle = \langle \psi \vert \hat{\mathbf{\mu}} \vert \psi \rangle$
But I don't feel the physical sense in the case…
jacksonslsmg4
- 169
12
votes
2 answers
What is the "direction" of the transition dipole moment? (Understanding Eq. 9.29, Charge and Energy Transfer 3rd Ed, May & Kuhn)
For a real vector $\mathbf{r}$, the direction is given by: $\hat{\mathbf{n}}=\mathbf{r}/\left|\mathbf{r}\right|$.
The transition dipole moment is a complex vector. How do you define its direction?
The point of this question is that I am trying to…
a06e
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On Problem 2.2 in Griffiths' Introduction to Electrodynamics
In part (a) we were asked to find the electric field at a distance $z$ above the midpoint between two equal charges of magnitude $q$ that are a distance $d$ apart. I obtained the correct answer:
$$\frac{1}{4\pi…
Ambica Govind
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votes
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Why should a dipole have zero net charge?
Why can a dipole not have two unequal charges separated by a distance? Is there any significance for the dipole being defined as electrically neutral?
