# Dipole Definition and 52 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. ### Can the charges at the ends of a dipole in a polar molecule exceed unit charge?

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...
2. ### 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...
3. ### 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##...
4. ### Calculation of the field due to a dipole at an arbitrary point

I know how to derive field using ##E = -\nabla V## in polar coordinates and doing so gave me $$E = (kP/r^3)(1 + 3cos^3\theta)^{1/2}$$ now I am trying to derive ##E## at point P using the fields produced by +ve and -ve charge respectively and taking components of each along the radial direction...
5. ### Magnetic Potential Energy?

Recently I have encountered the following expression for the potential energy of a magnetic dipole of moment ##\boldsymbol{\mu}## placed in an external magnetostatic field B: $$U=-\boldsymbol{\mu} \cdot \textbf{B}$$. However, I was told that magnetic fields are non-conservative, so we can't...
6. ### Find the electric dipole moment for a water molecule

The equation that we saw in class is for a continuous charge distribution, I think that for this exercise I need to treat the system as a discrete charge distribution but I'm not sure. Also, I don't know how I can calculate the intensity of the electric field needed to move this charge.
7. ### Divergence of an Electric Field due to an ideal dipole

Given $$\vec E = -\nabla \phi$$ there $$\vec d \rightarrow 0, \phi(\vec r) = \frac {\vec p \cdot \vec r} {r^3}$$ and ##\vec p## is the dipole moment defined as $$\vec p = q\vec d$$ It's quite trivial to show that ##\nabla \times \vec E = \nabla \times (-\nabla \phi) = 0##. However, I want to...
8. ### What is the continuous electric dipole distribution?

An electric dipole is a system of two opposite point charges when their separation goes to zero and their charge goes to infinity in a way that the product of the charge and the separation remains finite. Now how can we have a continuous electric dipole volume distribution from such a...
9. ### Electric dipoles

What is the convention? Because the field lines leave the positive charges and enter the negative ones, do not they?
10. ### Calculate the magnitude and direction of the torque

Homework Statement [/B] a) (a) Assuming the HCl molecule consists of point-like ions (H+ and Cl) separated by 1.0 * 10^-10m, find the dipole moment of the molecule. b) Calculate the magnitude and direction of the torque exerted on this dipole if the molecule is subjected to an external electric...
11. ### I Falling electric dipole contradicts the equivalence principle?

Consider an electric dipole consisting of charges ##q## and ##-q##, both of mass ##m##, separated by a distance ##d##. If the dipole is given an acceleration ##a## perpendicular to its moment the total electric force on it, due to each charge acting on the other, is given approximately by...
12. ### Magnitude of an Electric Field due to a dipole

Homework Statement A dipole is located at the origin, and is composed of charged particles with charge +e and -e, separated by a distance 2x10-10m along the x-axis. Calculate the magnitude of the electric field due to the dipole at location ##\langle 0.2\times 10^{-8}, 0, 0\rangle##m Homework...
13. ### Electric Field due to dipole - solution check

Homework Statement Hi guys, my exam is in four days and my tutor for the electromagnetic module is neither very active nor very competent, so I would like you guys to check my solution for this question. I am afraid I might have messed up some signs or some linear algebra. Homework Equations...
14. ### Dipole problem with electric fields

Dipole problem (which is solved through mirror imaging) has been troubling me with its solution. I understand everything except how the dipole moment's coordinates came to be, since when converted into x-y axis, its doesn't make sense. (problem 4.6) The screenshot contains the solution which...
15. ### Someone help explain electric dipole situation

Ok so she says that electric dipoles are of opposite charge but equal magnitude at 3:40. But then at 5:33 she shows 2Q with -Q, at that point the magnitude of the 2Q particle wouldn't be equal to the -Q so they wouldn't be electrical dipoles right?
16. ### Charge-Dipole Derivation - Assumption That x >> a

In this derivation: https://cpb-us-e1.wpmucdn.com/sites.northwestern.edu/dist/8/1599/files/2017/06/taylor_series-14rhgdo.pdf they assume in equation (8) that x >> a in order to use the Taylor Expansion because a/x has difficult behavior. Why does that assumption work? Meaning, why can we...
17. ### How do I calculate the potential created by a dipole

Homework Statement I'm given that there is a positive charge of 1 nC at x=0.25 m and a negative charge of -1 nC at x=-0.25 m. I've calculated the potential created at different points along the x-axis by the positive charge and the negative charge using the formula, $$V=\frac{kq}{|r|},$$ where...
18. ### How do I draw Lewis Structure Diagrams? +1 More

Homework Statement : 2 Questions, sorry about this if It adds confusion. 1) How do I go about drawing Lewis Structure Diagrams? I've searched the web, but all I can find, even when they say it's a "Lewis structure" diagram is lewis dot diagrams. My teacher wants it in the specific form where...
19. L

### How to calculate the dipole moment of the spherical shell?

Homework Statement A spherical shell of radius R has a surface charge distribution σ = k sinφ. Calculate the dipole moment of the spherical shell. Homework Equations P[/B]' = ∫r' σ(r') da' The Attempt at a Solution So I believe my dipole will be directed along the y axis, as the function...
20. B

### Interactions between a dipole and a point charge

After solving a homework problem, I realized I don't know what to do when there's a dipole and a point charge but the distance from the charges in the dipole is greater than the distance from the center of the dipole to the charge. As my homework problem stated, with a little context added...
21. ### Obtaining position in a dipole field

Hi all, Consider one has a magnetic dipole, the field given by: $$\vec{B} = \frac{\mu_0}{4\pi}\left(\frac{3(\vec{m}\cdot\vec{r})\vec{r}}{r^5}-\frac{\vec{m}}{r^3}\right)$$ where we can take $$\vec{m} = m\hat{y}$$. Let us say we have the a magnet vector which is...
22. F

### I Angular dependance of NEXAFS spectroscopy - derivation

Hi all, this is my first time posting so I hope it's in the right place, if not I apologise. I'm trying to understand the angular dependence in NEXAFS spectroscopy for linearly polarised light. So from what I understand, the quantum mechanical description of the excitation process for a single...
23. ### Electric Field Intensity of a line on bisecting plane

Homework Statement A very thin, finite, and uniformly charged line of length 10 m carries a charge of 10 µC/m. Calculate the electric field intensity in a plane bisecting the line at ρ = 5 m. Homework Equations The Attempt at a Solution Not sure why I'm not getiting this but I've been at...
24. R

### Permanent Dipole - Permanent Dipole Interaction Derivation

Homework Statement I am trying to derive the dipole-dipole interaction derivation, which is: U=(-p1p2/4πϵ_0) (1/z^3) ((2cosθ_1cosθ_2)− (sinθ_1sinθ_2cosζ)) Where p1 and p21 are the two dipole moments, r is the distance between two dipoles on the y axis, θ_1 and θ_2 are the angles between the...
25. ### B LED in dipole antenna

Hi. In this video around 6:45, this guy builds a simple dipole antenna with an LED and capacitor in parallel in the center. The LED flickers when close to a transmitting cellphone. Since the LED only let's current pass in one direction, shouldn't this quickly lead to a charge imbalance between...
26. ### Forces between the dipole and a point charge

Homework Statement We have an electric dipole with moment P=2*[10][/-5] pointing in x direction. What is the force experieced by dipole at origin when a point charge Q=3*[10][/-4] is located at (0.014 m ,0,0) Homework Equations 1. [E][/dipole]=(1/4π[ε][/0])(2p/r3) 2. p=qs 3. F=qE 4. τ=pEsinϑ...
27. ### Phase difference between magnetic and electric field

When solving the differential equations for an electromagnetic wave you get out that the electric and magnetic field oscillate in phase. But when considering a oscillating dipole, the electric and magnetic field at a point close to the dipole are a quater period out of phase. Can someone please...
28. ### I Dipole: Which field lines go to infinity?

Hi. An electric dipole field (two opposite point charges separated by some distance) has fields lines from the positive to the negative charge, but also field lines reaching to and coming from infinity. Starting from the positive charge, is there a way to compute the opening angle of the cone...
29. ### Torque and work of dipole

Homework Statement An electric dipole consists of +/- Q = 330nC separated by a distance of 1200nm. The dipole is initially oriented in the -i direction (along the negative x axis). The dipole is in a uniform external electric field of E=2500j N/C Determine the following: a) The magnitude of...
30. ### Is there such thing as magnetic interference?

Say I place a magnet on a table, and I have a metal in close proximity. Will its magnetic field change due to the presence of this metal, however minute? What if I had another magnet or the table itself is made of materials the magnet is slightly attracted to? Does this phenomenon even exist?
31. ### Net force in a Non-Uniform magnetic field

When there is a magnetic dipole placed in an external non uniform magnetic field, will it experience a net force?
32. ### Potential Energy for dipole in Electric Field

Homework Statement To derive Potential Energy for dipole p in Electric Field E. 2. Homework Equations Potential Energy is the work done by the external agent in turning the angle of the dipole from the U=0 position to another position against the influence of the electric field applied...
33. ### Question about polarization density

Homework Statement Given a sphere with radius R, centered at (0,0,0), it's dipole density given as ##P\left(\vec{r}\right)=\alpha\left(R-r\right)\hat{z}## where r is the distance from the center of the ball. I'm required to find: Bound charge density inside the sphere, bound charge density on...
34. ### Dipole moment arrows confusion

My teacher posted on his website, Lewis structures of different compounds. One of them were N3- Why isn't there a dipole moment arrow pointing from the central atom to the other Nitrogen? Does the arrow only point from neutral atom to negatively charged atom?
35. ### I Effect of SAM physisorbed on graphene - some questions

Hello everyone! :) I'm sorry that I'm posting something that might be obvious, but I'm still struggling to capture all the concepts behind the fundamental physics of this model. Let's say, I have a 2D sheet of graphene, on which, there's a physisorbed layer of molecular dipoles (vdW bonding...
36. ### Thin rod w/linear charge density, dipole moment

Homework Statement A thin rod of length 2L has a linear charge density that isλ0 at the left end but decreases linearly with distance going from left to right in such a way that the charge on the entire rod is zero. Given E = −kλ0/L(d/(L−d)−ln(d−L)+d/(L+d)+ln(L+d)) for a point P that is...
37. ### Chemistry Why does NCl3 has dipole-dipole intermolecular force?

Hello! I will be grateful for the explanation on why NCl3 has a dipole-dipole intermolecular force, if, based on electronegativity difference, or rather the absence of such, (both N and Cl have 3.0 electronegativity) this is a non-polar bond? Thank you!
38. ### Force on a dipole moving through a magnetic field

Homework Statement A dipole of moment ##\vec{p}## where p is fixed, moves with velocity ##\vec{v}## though a magnetic field ##\vec{B}##. Show that the force on the dipole is ##\vec{v}\times(\vec{p}\cdot\vec{\nabla})\vec{B}+\dot{\vec{p}}\times\vec{B}##. Homework Equations...
39. ### Method of images about a sphere with a dipole

Homework Statement Hello everyone, I am new here and have a question regarding method of images in my electricity and magnetism class. I need help to even get the ball rolling. The question is as follows: a) What is the image of a dipole, oriented toward the center of the conducting sphere, if...
40. ### Mathematica Rotation of 3D Plot using Euler angles

So, I'm trying to plot a 3D "dipole" (an arrow with a small torus around it basically) in mathematica, and want to rotate it according to Euler angles... I use this code for the rotation matrix: rot[a, b, g] := RotationMatrix[g, {1, 0, 0}].RotationMatrix[b, {0, 1, 0}].RotationMatrix[a, {0, 0...
41. ### Series expansion for 2D dipole displaced from the origin

I learn that we can expand the electric potential in an infinite series of rho and cos(n*phi) when solving the Laplace equation in polar coordinates. The problem I want to consider is the expansion for the potential due to a 2D line dipole (two infinitely-long line charge separated by a small...
42. ### Potential of a magnetic dipole

Hello everyone! I'm stuck at an Electrodynamics problem and would be happy for some guidance 1. Homework Statement A magnetic dipole \vec{m}(t)=\vec{m}_0cos(\omega t) at the origin can be described by the current density \vec{j}(\vec{r},t)=-\vec{m}(t)\times\vec{\nabla}\delta(\vec{r})...
43. ### Current dipole

Hi all, new user here. I did a search on Google for "current dipole" during an idle moment, and discovered this forum and joined. There was an old, closed thread concerning "current dipole", started by basheersubei and including tiny-tim, sophiecentaur, and madness, which closed 3.5 years ago...
44. ### Charge and Electric Field Problem

Homework Statement You have been hired by Brockovich Research and Consulting (BRC) to research a new water purification device that uses seeds from the Moringa Oleifera trees.1 A protein in the seed binds to impurities causing them to aggregate so that the clusters can be separated from the...
45. ### Bow Tie Antenna Construction Question

I'm trying to build a high gain TV antenna. I'm looking to achieve a 75 mile minimum range under most weather conditions. I do have a signal amp board I striped from an OK antenna, that I plan to use as well. I'm trying to specialize the antenna for my viewing market, UHF channels 17-38 (489.25...
46. ### Do ionic crystals have total electric dipole moment?

I have come up with a paradox: Ionic crystals, in which cations and anions form a lattice, seems to have total electric dipole moment! For example, consider a one dimensional example: ##+ - + - + - ... + - + -## In the above picture, a ##+## represents a cation and a ##-## represents an anion...
47. ### Magnetic Dipole due to an electron's orbital motion

Homework Statement Select all of the following which are possible combinations of Lz and θ for hydrogen atoms in a d state, where Lz is the z component of the angular momentum L, and θ is the angle between the +zaxis and the magnetic dipole moment µℓ due to the electron's orbital motion...
48. ### Electric Dipole Radiation from a Spinning Current Loop

Homework Statement Hi everyone, My problem is fairly simple: We have a circular current loop enclosing area A, and with a constant current I. The loop is rotating about its diameter at a constant angular frequency \omega. All we need to do is find the electric dipole, and magnetic dipole...
49. ### Electric field due to dipole in polar coordinates

For a dipole, if there is point subtending an angle ##\theta## at the centre of dipole and at a distance ##r## from centre of dipole, then the electric field at that point can be broken into 2 components. One along the line joining the point and centre of dipole and point given by...
50. ### Electric dipole moment for a uniformly charged ring

Homework Statement Text description: Let V(z) be the potential of a ring of charge on the axis of symmetry at distance z from the center. Obtain the first two non-vanishing terms of the multipole expansion for V(z) with z>>a where a is the radius of the ring. Can you see by symmetry that the...