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Why should a dipole have zero net charge?

The concept of a dipole moment, and other moments such as a monopole, quadrupole, etc, comes from the process of writing a field as a sum of components called multipoles. This is known as a multipole ...
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28 votes
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Why there is no dipole gravitational wave?

The simple Newton-like explanation of dipole gravitational radiation unexistence is following. The gravitational analog of electric dipole moment is $$ \mathbf d = \sum_{\text{particles}}m_{p}\mathbf ...
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21 votes

Why is dipole the simplest source in electrodynamics?

The smallest radiating unit is an accelerating dipole moment. That can of course be produced by an accelerated single charge, which can be made equivalent to an oscillating dipole. $$ \ddot{p} = q\...
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18 votes
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Do neutrons exhibit momentary small charges due to the movement of its quarks?

It seems that within the standard model of particle physics A permanent electric dipole moment of a fundamental particle violates both parity (P) and time reversal symmetry (T). These violations ...
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17 votes
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Electric field due to a hydrogen atom

Especially the hydrogen atom, with a proton in the nucleus and an electron revolving acting as a dipole This is a problematic way of understanding the hydrogen atom ─ it basically tries to insist on ...
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13 votes
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Why is dipole the simplest source in electrodynamics?

You are correct that in electrodynamics the only real sources of radiation are non-uniformly moving charges. However, when you solve for the potentials, you get some intricate expressions, the so-...
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12 votes

Why is dipole the simplest source in electrodynamics?

Simple reason: an oscillating monopole field in a region isolated from currents would violate charge conservation. Note a monopole field is not the same as an oscillating monopole charge, which, as ...
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11 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?

According to the Lorentz transformation formula for the electric field, we have: $$ \mathbf E_\perp' = \gamma(\mathbf E_\perp+\mathbf v\times \mathbf B_\perp) $$ Since $\mathbf B=0$ in the rest frame, ...
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9 votes
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Derivation of Interaction energy of Dipole - Induced Dipole Interaction

I don't think you need quantum mechanics to understand what's going on in dipole-induced dipole interaction. The basic mechanism is quite simple and just the details of the calculations change by ...
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8 votes

What do we mean with magnetic monopole and dipole?

What do we mean with magnetic monopole and dipole? I can not find a way to relate magnetic monopoles and dipoles with electric ones. I do not understand their outcomes. Luckily, there exists a ...
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8 votes
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Does an accelerating electric dipole radiate?

Summary: A dipole moving through space radiates. Specifically, the power radiated depends both on the dipole's acceleration and its jerk. Finding the potentials: Consider an idealized dipole $\...
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8 votes

(Special relativity) A tilted dipole composed of $+q$ and $-q$ point charges moves at a horizontal velocity. Will it rotate?

Ricky Tensor has beaten me to the punch, and his excellent answer provides the key insight: in the frame where the stick is moving, the force of the stick on the charges is not parallel to the stick ...
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8 votes

How does zero electric field look like?

The key word in your post is net. Only the net flux must be zero, which means as much of the field must be pointing in as is pointing out of the surface. Look at this visualisation from Wikipedia If ...
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7 votes

Why does the field of an electric dipole drop off as $1/r^3$?

Very simply, the field of the positive and negative elements of the dipole "almost" cancel out - but not quite. It is because they are some small distance away that there is a residual (third order) ...
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7 votes
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Does a neutral particle feel the electric pull?

neutral atom, Most chemistry happens between neutral atoms. There are the so called "spill over" forces , like the van der Waals ones, which allow for electromagnetic bondings between atoms and ...
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7 votes

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

Well, let’s start with a static electric field: the electrons would move in the opposite direction of it and the nucleus in the same direction. But the nucleus’ and the electrons’ attractive force ...
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  • 493
6 votes

Why is the geomagnetic north pole at a different location from the magnetic north pole?

Earth's magnetic field isn't really a dipole, but a dynamic field due to the convection occurring in the planet's core (consists of molten iron). The model below shows a simulation of the magnetic ...
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6 votes
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Why does the dipole moment depend on the distance?

The electric dipole moment is defined as $$p = \int r \;\mathrm dq$$ In the case of a pair of charges for which both charges are of the same magnitude, the choice of the origin turns out to be ...
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6 votes
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Convention for the potential energy of a dipole in a uniform electric field?

It's a matter of choice. You can set the potential energy to be any value at any angle. You don't even have to have a zero-value at all; you could make $U$ purely positive or purely negative if you're ...
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6 votes
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If a water molecule is neutral, how do water molecules attract one another by electric force and form water?

The water molecule is neutral on overall basis, i.e: the water molecule as a whole has no net charge. The water molecule is not linear rather it has a bent shape with two hydrogens on the same side. ...
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  • 6,903
6 votes

Dipole Moment between two charges of different magnitudes but opposite signs

If the net charge in your system is non zero, the dipole moment is not unique and depends on the origin. Hence the question "what is the dipole moment?" is meaningless without specifying the origin. ...
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6 votes
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Is there a finite-sized charge distribution whose electric field is *exactly* that of a point dipole?

Yes, this is perfectly possible The way you do this is by choosing a charge distribution which is 'completely dipolar' in some suitable sense, and this will produce an electric field which is also a ...
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6 votes
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How to derive the $\frac{4\pi}{3}\vec{p}\delta^3(\vec{r})$ element for the dipole field, from its potential?

Hint: Formally one should introduce testfunctions to deal with distributions. Another more physical approach is to regularize the dipole potential $$ \Phi_{\varepsilon}~=~ \frac{\vec{p}\cdot\vec{r}}{(...
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6 votes
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Difference between magnetic dipole interactions and spin interactions

The origin of magnetism is an complex problem in solid physics, (may be the the most lasting discussion in condensed matter physics). My point is: if caring about interaction of spin in system, we ...
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6 votes

(Special relativity) A tilted dipole composed of $+q$ and $-q$ point charges moves at a horizontal velocity. Will it rotate?

Here I am providing a shorter version of Ricky Tensor's excellent answer to this question. In the frame where the dipole is at rest, each of the charges feels an electro(magnetic) force along the line ...
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  • 367
6 votes

Is it possible to have a particle with a positive and negative charge?

To understand particles at the level of very small distances requires at least a little quantum mechanics. Consider positronium. This is a bound state of an electron (charge -1) and a positron (charge ...
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5 votes

Force between two point dipoles

Going from the field to the force will be difficult, because you don't know a priori how a dipole reacts to a field, particularly if the field is not homogeneous. The way to do this is the same as you ...
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5 votes

How does $E = -\nabla V$ work for a dipole?

You are making the mistake of thinking of the gradient as a regular one dimensional function where you pop in a value and it throws out an output. You can't take the gradient of a number (in your case,...
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5 votes

Why does magnetic force vary in proportion to the cube of the distance instead of the square?

It is just a consequence of the fact that the multipole expansion of an arbitrary magnetic field configuration doesn't have a monopole term due to absence of magnetic charges, and the first non-zero ...
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5 votes

Why does magnetic force vary in proportion to the cube of the distance instead of the square?

For the case of the gravitational potential, it is true that a point mass (gravitational monopole) generates a field that goes as $\mathcal{G}_{ \rm monopole}\sim 1/r^2$, or equivalently, a potential ...
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