# What is Dipole: Definition and 852 Discussions

In electromagnetism, there are two kinds of dipoles:

An electric dipole deals with the separation of the positive and negative charges found in any electromagnetic system. A simple example of this system is a pair of electric charges of equal magnitude but opposite sign separated by some typically small distance. (A permanent electric dipole is called an electret.)
A magnetic dipole is the closed circulation of an electric current system. A simple example is a single loop of wire with constant current through it. A bar magnet is an example of a magnet with a permanent magnetic dipole moment.Dipoles, whether electric or magnetic, can be characterized by their dipole moment, a vector quantity. For the simple electric dipole, the electric dipole moment points from the negative charge towards the positive charge, and has a magnitude equal to the strength of each charge times the separation between the charges. (To be precise: for the definition of the dipole moment, one should always consider the "dipole limit", where, for example, the distance of the generating charges should converge to 0 while simultaneously, the charge strength should diverge to infinity in such a way that the product remains a positive constant.)
For the magnetic (dipole) current loop, the magnetic dipole moment points through the loop (according to the right hand grip rule), with a magnitude equal to the current in the loop times the area of the loop.
Similar to magnetic current loops, the electron particle and some other fundamental particles have magnetic dipole moments, as an electron generates a magnetic field identical to that generated by a very small current loop. However, an electron's magnetic dipole moment is not due to a current loop, but to an intrinsic property of the electron. The electron may also have an electric dipole moment though such has yet to be observed (see electron electric dipole moment).

A permanent magnet, such as a bar magnet, owes its magnetism to the intrinsic magnetic dipole moment of the electron. The two ends of a bar magnet are referred to as poles—not to be confused with monopoles, see Classification below)—and may be labeled "north" and "south". In terms of the Earth's magnetic field, they are respectively "north-seeking" and "south-seeking" poles: if the magnet were freely suspended in the Earth's magnetic field, the north-seeking pole would point towards the north and the south-seeking pole would point towards the south. The dipole moment of the bar magnet points from its magnetic south to its magnetic north pole. In a magnetic compass, the north pole of a bar magnet points north. However, that means that Earth's geomagnetic north pole is the south pole (south-seeking pole) of its dipole moment and vice versa.
The only known mechanisms for the creation of magnetic dipoles are by current loops or quantum-mechanical spin since the existence of magnetic monopoles has never been experimentally demonstrated.
The term comes from the Greek δίς (dis), "twice" and πόλος (polos), "axis".

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1. ### Field due to an electric dipole (Halliday & Resnick, Ch. 27 problem 23)

Using either H&R's Chapter 27 Example 3 or Problem 590 of the ##\mathbf{Physics Problem Solver}##, I've been unable to get the component ##E_x## or ##E_y##. There are now different angles at the charges. My thanks to berkeman for LaTeX advice, but any errors are of course my own. Thanks in...
2. ### Magnetic dipole moment and integration surfaces (Introductory Electromagnetics - Magnetistatics)

A current current loop is running through this figure. How do I design integration surfaces to find the magnetic dipole moment? In the solution the three following figures were designed for integration surface, and they prove that they all give the same answer of ## m= 2IRd \hat{z} ##. For...
3. ### I Why charge density of moving dipole is dependent on time?

This paper aims to resolve the inconsistency between different transformation equations by expressing the electric current created by a moving electric dipole as the sum of polarization and magnetization currents and calculating the resulting magnetic field. Here they take charge density to be...

8. ### I The electric field due to a dipole

and Can someone explain how they made these equations like this? How did the radius become that equation? What formulas from algebra did they applied? I'm looking at these formulas and I don't understand how r=z+1/2*d
9. ### Find the Electric field due to an electric dipole at the origin

Question : I have tried to solve but I struggle with this part: Any help would be appreciated.
10. ### A Bound states of an electron trapped in a dipole field

The problem of bound states of an electron trapped in a dipole field is being studied by Alhaidari and company. (See, for example, https://arxiv.org/ftp/arxiv/papers/0707/0707.3510.pdf). It is not clear to me why the point dipole approximation is used everywhere in such calculations. Can't an...
11. ### Equipotential surfaces for an electric dipole

The answer is given as (a), but I think it's not correct based on the equipotential surfaces diagram given in our book for an electric dipole as below. The red dashed lines, which are supposed to be the equipotential surfaces, are surely not representing a sphere centred at the dipole center...
12. ### External forces required to move an electric dipole quasi-statically

If the dipole is to be in equilibrium at all positions as it's moved so that it's always inclined at 60° to the horizontal, then the torque due to electric field needs to be balanced by torque due to external forces ##F_{ext}## as shown in above diagrams. But such external forces will not make...
13. ### Understanding the energy of a dipole in a uniform electric field

Griffith's E&M problem 4.7 asks to calculate the energy of a dipole in a uniform electric field and I ended up getting a different answer than the one given. I thought that calculating the energy/work done to construct the dipole is the same as dragging two point charges where one is d apart...
14. ### MIT OCW, 8.02 Electromagnetism: Potential for an Electric Dipole

Here is a depiction of the problem a) The potential at any point P due to a charge q is given by ##\frac{kq}{r}=\frac{kq}{\lvert \vec{r}_s-\vec{r}_P \rvert}##, where ##r## is the distance from the charge to point P, which is the length of the vector difference between ##\vec{r}_s##, the...
15. ### Why a particle with spin=0 can't posses a magnetic dipole moment?

Hi, I would like to know why a particle with spin=0 can't posses a magnetic dipole moment? Using Wigner-Eckart theorem for ##\langle j,1,m,0|j,m \rangle## I get ##\langle j'|| \vec{J}|| j \rangle = \hbar \sqrt{j(j+1)} \delta_{jj'}## It seems like the right hand side is the magnetic dipole...
16. ### Optimizing Polar Axis for Dipole in Polar Coordinates

I don't know how to get the result referring to the previous task. Is my decision correct?
17. ### Magnitude of external electric force on electric dipole

For this part(b) of this problem, how is the magnitude of the total electric force zero? I thought it would be: If they asked for the total electric force, then I would have said zero because the two electric force vectors cancel. Many thanks!
18. ### A Induced dipole moment (adiabatic) following the rotating E-field

Hello! Assume I have a 2 level system, where the 2 levels have opposite parity. If I apply an electric field, I will get an induced dipole moment. For now I want to keep it general, so the induced dipole moment can be very large, too. Let's say that I start rotating this electric field in the...
19. ### I Question about orbital and spin magnetic dipole

Hello guys, i want to ask you a question about orbital and spin dipole, and how this is going to influence diamagnetic or paramagnetic substances. So my question is: we know in a atom there is orbital and spin motion by electrons so possibly two magnetic dipoles. Is it correct to say that in...
20. ### I Question regarding how to interpret dipole moment for bound charges

How do I interpret physically what dipole moment is ? The explanations that I received were "two charges seperated by a small distance " ,"it talks about ability of a dipole to rotate under the influence of an Electric Field " ,"Second term of the Multipole expansion" ,I get that these terms...
21. ### Limits of Partial Charges in Dipoles

In my book it is written "Ends of dipole possesses partial charges. Partial charges are always less than the unit electronic charge (1.6×10−19 C)". Suppose in a double bond(two electron is shared by each atom) or triple bond(three electrons are shared by each atom), can the electronegative atom...
22. ### B Direction of Electric Field & Field Due to a Dipole

Hi all. I am stuck with a seemingly silly doubt all of a sudden. The direction of Electric Field is taken from Positive to Negative (because Field Lines originate from a Positive Charge and terminate at Negative Charge). We know that direction of Dipole Moment is from Negative Charge to a...
23. ### Impedance of a half-wave dipole antenna

73 + j42 means it has an active resistance plus reactance. But this "active" resistance is not a DC resistance, right? We can't just measure 73 ohm with a multimeter since the circuit is open. What closes it then? Let's say the reactive part is zero. How do we measure 73 ohm? By measuring...
24. ### I How an induced electric dipole vibrates with EM field

If we have an electromagnetic wave like the one in the picture and a molecule which is, in the image, the small black ball with electron cloud being the part with "minus sign" in it, does the molecule with its cloud start to oscillate, once the EM wave hits it, as an induced electric dipole...
25. ### Laplace's equation when there is a point dipole

I know the solution already, yet I don't understand why I'm able to solve laplace's equation when the volume has a point dipole within; I thought this required Poisson's eauation, which I have no experience in solving. Here is the relevant part of the solution
26. ### Griffith's problem 4.37 -- A point dipole at the center of a sphere of linear dielectric material

I tried to solve it for some time and then looked at the solution manual, which got me completely lost. Those are the first lines of the solution : I'm not so sure how equation 4.39: makes him conclude that the same relation holds for dipole moments. My second concern is that I'm not sure how...
27. ### I Transition Dipole Moments for Strontium

Hey all, I am currently looking for some data on the resonant transition dipole moment for the Rydberg states of Strontium (in the literature, the square of the dipole moment is known as the "C3 coefficient"). If anyone could point me to some relevant papers that would be greatly appreciated.
28. ### I Laplace's equation in presence of a dipole (perfect or physical)

Does Laplace's equation hold true for electrostatic potential at the location of a dipole? Or should poisson's equation be used?
29. ### I Dipole moment of a cylinder of uniform polarization

If I want to calculate the dipole moment of a dielectric cylinder of uniform polarization perpendicular to its axis, I could multiply the polarization by the volume of the cylinder, which is okay. But another method is to consider the cylinder to be a superposition of two cylinders of equal and...
30. ### Potential vector of a oscilating dipole:

I am passing through some difficulties to understand the reasoning to derive the electric potential of an oscilating dipole used by Griffths at his Electrodynamics book: Knowing that ##t_o = t - r/c##, What exactly he has used here to go from the first term after "and hence" to the second term...
31. ### I Understanding the diagonal elements of the transition dipole moment

Hey guys, I just numerically calculated the matrix elements for a superconducting qubit and I'm having some trouble to interpret the result. I will include a plot of the matrix I got below: I basically have "large" non zero elements on the main diagonal of this matrix. In previous courses I...
32. ### I Exact electrostatic potential of a pure dipole using multipole expansion

If I have a physical dipole with dipole moment p. Now, this formula for potential (V) is a good approximation when r is much larger than both r1 and r2 in the picture below. It's however said that for a pure dipole for which the separation between charges goes to zero and q goes to infinity, the...
33. ### I Will this dipole rotate or change position?

Will this dipole rotate or change position? The external electric field is in black. Two charges with their electric fields are drawn in orange.
34. ### What is the length of each side of a resonant dipole to receive 12MHz?

Hi, a question: Construct a resonant dipole to receive 12MHz. Answer; λ = c/f = (3x10^8) / (12 x10^6) = 25m The dipole length λ/2 = 12.5m The length of each side dipole is 12.5m/2 = 6.25m Im confused, isn’t it the answer is 12.5m? Why require to divide 12.5m/2 again to get the answer...
35. ### I Something about retarded potentials for oscillating electric dipole

In a problem of an oscillating electric dipole, under appropriate conditions, one can find, for the potential vector calculated at the point ##\vec{r}##, the expression ##\vec{A}=\hat{k}\frac{\mu_0I_0d}{4\pi}\frac{cos(\omega(t-r/c))}{r}## where: ##\hat{k}## is the direction of the ##z-axis##...
36. ### A Calculation of dipole and quadrupole momentum of CO

This is my first post of this topic so I hope it is in the correct place. I need some help to figure out the using of GAUSSIAN in order of calculate the dipole and quadrupole moment for the carbon monoxide molecule with different levels of theory (SCF and Post Hartree Fock methods). In...
37. ### Work done on dipole and potential energy in uniform electric field

I encountered a problem regarding the appropriate sign needed to be taken for the work done on a dipole when it rotates in a uniform electric field and would appreciate some help. The torque on a dipole can be defined as τ=PEsinθ The work done on a dipole to move it from an angle ##\theta_0##...
38. ### I Estimation of E-field strength at a distance from dipole antenna

Hello everyone, I was asking myself about electric field strength estimation at a distance d from - in my case - a half wave dipole antenna. There are pretty much a lot of information about this on internet or in books but still, there are a few things that are confusing to me that I would...
39. ### B Why does charge oscillate in an electric dipole antenna?

Picture: Energy source => LR Oscillator => Transformer => Transmission line => Electric dipole antenna => traveling wave Why would the charge even oscillate in the antenna as opposed to building up in the antenna? The transmission line + antenna is not a closed circuit right?
40. ### Work done on a magnetic dipole (compass needle rotating)

So this is a sketch I made of the situation and this is my approach my approach is incorrect , and Idon't seem to find the mistake , maybe B*p isn't correct. Any ideas?
41. ### I What are the Cosmological monopole and dipole?

Hi there I'm currently studying cosmology but I'm having a hard time grasping that concept of the cosmological monopole and dipole (quadrupole etc) and was wondering if someone could explain what they are conceptually and physically. Thanks : )
42. ### Magnetostatiscs: dipole moment and magnetic field

Hello! I tried to solve a) see figure below, is it correct? b) so what I think I can do is to solve ## M_{12} ## from the equation of the magnetic flux then I will get ## \frac{\Phi}{I} = M_{12}## Then I can even use the equation får the magnetic flux and the magnetic field  \Phi = \int \vec...
43. ### Why Does the Potential Energy Calculation for a Dipole Yield a Negative Value?

So the change in potential energy is ∆U = Uf-Ui. Final minus initial. If i solve the above problem like this I end up with a negative value. The way the person in the attached work solved the problem, is they used ∆U = Ui-Uf. How are the switching Ui and Uf? What is it I am missing?
44. ### Dipole placed in a uniform electric field

My understanding is that the uniform electric field ##\vec E## cannot be the net electric field since the dipole creates its own electric field as shown in first diagram below, which must superimpose with the uniform electric field. So, yes, the uniform electric field ##\vec E## around the...
45. ### I Magnetic dipole in vacuum near absolute zero

Consider a single atom (or particle) in a vacuum (without electric, magnetic or gravitational field) at near zero kelvin (i.e., no photons or particles striking it). I am curious if it will still have a magnetic dipole? If there still is (which I believe), had this been shown experimentally?
46. ### I How to recalculate Berry phase dipole moments (jumps over time)?

Is there anyone out there who can help a newbie understand how to deal with Berry phase dipole moment data? I ran a simulation to calculate dipole moments over time using the Berry phase method. The problem is that there are jumps in my data. There is an example at the end of this post (part...
47. ### I Dipole moment of Rydberg states

Hello! Are there any experimental measurements or theoretical calculations of the electric dipole moment of any Rydberg state for CaF or BaF? Thank you!
48. ### Force on a dipole in a non uniform electric field

I have figured out how the force is towards left in the first case. I think it is due to the larger force on - charge. Please help me out with the second and third case.
49. ### I Orbital magnetic dipole moment of a proton

hi every one what is the amount of orbital magnetic dipole moment of proton? this different with the intrinsic magnetic.
50. ### Calculating Radiation Pattern for a grid of two rows of dipole antennas

Although problem says sketch, what I really want is the formulae by θ for the radiation. After trying this for a while I cheated and looked at the solution. I still can't figure out the steps on how to get to the solution. the answer is: What I tried: I'll assume that the intensity from a...