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".
Hi all,
I've been having a problem with understanding some of the van der Waals forces. I understand that the polarizability of a induced-fixed dipole interation is:
\begin{equation}\alpha =4\pi\epsilon r^{3} \end{equation}
Which leads to the potential field (assuming two different...
Homework Statement
Two point charges q1 = 2\muC and q2 = -2\muC are placed at r1 = (3,0,0) m and r2 = (0,0,4)m respectively
i) What is the force of q1 (in vector form)?
ii) What is the electric field at the origin?
iii) What is the electric dipole moment of this arrangement (in vector...
I hope that I have chosen the correct thread and that this belongs here.
I understand the concept of a dipole, where you have opposite polarities at each end of a lineal object, i.e. a magnet. My question concerns the case of a sphere, where the outer surface is one polarity and the center is...
Hi.
So, you surround a ferromagnet with a solenoid.
Run current through solenoid to create B field withing.
2 Questions:
1:Why do the magnetic dipole moments in the ferromagnet "align" with the magnetic field of the solenoid? Doesn't lenz's law say that the magnetic field within the...
Homework Statement
Calculate the electric potential due to a tiny dipole whose dipole moment is 6.0×10^−30 C*m at a point 3.6×10^−9 m away for the following cases.
a) This point is along the axis of the dipole nearer the positive charge.
b) This point is 45 degrees above the axis but...
Homework Statement
A dipole p is situated at thecentre of a spherical cavity of radius a in an infiite medium of relative permitivity \epsilon_r . show that the potential in the dielectric medium is the same as would be produced by a dipole p' immersed in a continuous dielectric, where...
Longo, "Detection of a Dipole in the Handedness of Spiral Galaxies with Redshifts z ~ 0.04," 2011, http://arxiv.org/abs/1104.2815
If this is right, then I guess it would be the first possible hint of a nonzero rate of rotation for the universe. He doesn't attempt to state his results in terms...
Homework Statement
Having problems with this subject. Given hydrogenic carbon, with binding energies of
490 eV (1s) 857.50 eV (2p) 925.54 eV (3p) 949.36 eV (4p). Find wavelengths of all lines due to electric dipole transitions between the levels. State which you expect to be strongest...
Dear All,
I have a question that is afflicting me and I would be glad if you can give me an answer. I have a dipole in vacuum put at a certain distance from the surface of a dielectric material. I know the entity of the dipole, I know the distance from the surface and I know the interaction...
Yeah it's true, I heard him talking all about it tonight. He said he came up with the theory for it a while ago and he heard of it recently then he knew he was right.
Among other things, he briefly said he connected quantum mechanics and consciousness. Then to top it off he said physicists...
Homework Statement
Hi,
This is supposed to be simple, so I guess I miss something..
We have charge q at x1=d*cos (w*t), y=0, z=0. and charge -q at
x2=-d*cos (w*t), y=0, z=0. I need to do Fourier transform to the charge density.
Homework Equations
The Fourier transform is ...
Hi all,
I know that the electric field generated by a dipole is given by
\mathbf{E}= [1-i(\omega/c) r]\frac{3 (\mathbf{p}\cdot\mathbf{r})\mathbf{r}-\mathbf{p} }{r^3}+(\omega/c)^2\frac{\mathbf{p}-(\mathbf{p}\cdot\mathbf{r})\mathbf{r}}{r} e^{i(\omega/c)r}
where \mathbf{p} is the dipole's...
Homework Statement
Derive equation of torque: G = p X E from equation U = -p\cdotE
Homework Equations
G = \int x \times \rho(x)E dV
U = \int \rho(x)x \cdot \nabla\varphi dV
The Attempt at a Solution
I tried to figure how to represent G in a way that better express the nature...
Homework Statement
i just have a few questions about the radiation pattern of a half wave dipole antenna.
firstly i know the for the half wave dipole we can dervie and expression for the electric field in the zenith angle and the magnetic field in the azimutal angle by using the far field...
Homework Statement
Given a sphere radius R with surface charge density \rho_s=k\;cos\theta. Find the dipole moment \;\vec p.
Homework Equations
\vec p=\int \vec r'\rho_s \;d a = \int_0^{2\pi}\int_0^{\pi}\vec r' k\;cos\theta\; R^2d\theta\;d\phi
The Attempt at a Solution
To me, \vec r' =...
A hydrogen atom placed in an electrical field results in a changed energy level and a changed eigenfunction, compared to the free atom. To examine this effect, we choose a homogenous electrical field of the force F, whose field lines run along parallel to the z-axis. The Schrödinger equation is...
Homework Statement
It's me again:)
I have an antenna which emit the electrica power with the formula P given at the relevant equations. Now I shall calculate the impendance which the current generator "recognizes" which feeds the antenna with the current.
Homework Equations...
This is part of derivation of electric dipole potential where:
V(\vec r,t)=\frac 1 {4\pi \epsilon_0} \left [ \frac {q_0 cos [\omega(t- \frac {\eta_+} c )]}{\eta_+}- \frac {q_0 cos [\omega(t- \frac {\eta_- } c)]}{\eta_-} \right ]
\vec {\eta_+} = \vec r - \vec r^+ (t_r) \;,\; \eta...
I have a Nickel cylinder, 5 micron in diameter and 10 micron in length. I know the external field \vec{B} is 80 gauss, what is the formula for the magnetic dipole moment of this cylinder in the field?
Now I only have the formula for magnetic dipole of spheres, which is \mu = \frac{4}{3}\pi...
Homework Statement
An EM wave traveling in vacuum has a magnetic field in the lab frame K which is given by \vec{B}(\vec{x},t) = \hat{z} B0 \cos{kx-\omega t}
where Bo, k are positive constants and omega = ck.
a) A point magnetic dipole, m, where m = \hat{y}m0 (m0 constant) is at rest in...
Homework Statement
A molecule possessing a magnetic dipole moment has squared spin angular momentum 3/4 h bar. give an expression for the energy of the molecule when it is stationary in a magnetic field of flux density B.
Write down the partition function Z.
Homework Equations...
Hi
I have a question about the electric field of a dipole located at the origin. We know that the
coordinate free form for the electric field of a dipole is
\vec{\mathbf{E}}=\frac{1}{4\pi \epsilon_o}\frac{1}{r^3}\left[\frac{3(\vec{p}\cdot \vec{r})\vec{r}}{r^2}-\vec{p}\right]
Now let...
hi
i have two questions :smile:, that i cannot solve by my own:
does anybody know how to calculate the potential energy of two quadrupole moments that are separated by a distance r?( i looked for it in all my physics books, but i did not find anything at all)
and: if you have two...
Electric field of a dipole, two different equations??
Hi,
I've been taught in uni how to derive the electric field of a dipole to be
E= k p [2cos theta r(hat) + sin theta theta(hat)]/(r^3)
where k=1/(4pi e0), p=qd= dipole moment, (hat) terms are unit vectors and r is the distance...
Hi,
What direction does the electron's total magnetic dipole moment point relative to it's total angular momentum vector L+S? It seems to me that it would point oppositely to J=L+S since the spin magnetic dipole moment and the orbital magnetic dipole moment are both opposite to L and S, but...
Homework Statement
write down an expression for the electric potential of an electric dipole at a large distance
Homework Equations
V=(qa cos(theta))/(4 pi epsilon r^2)
The Attempt at a Solution
is 'r' the distance they are talking about or is it 'a'?
either way, if i substitute in...
does anyone know why the forces point in such a direction?
basically, its a dipole (y-orient) in an E-field
but why do the forces on the +q and -q slant as such?
thanks
Homework Statement
An electric dipole placed in a uniform electric field experiences a torque which tends to align the dipole parallel to the field. At the same time, due to two equal and unlike parallel forces Eq and -Eq acting at q and -q, the net force is zero. When the net force is zero...
Homework Statement
[PLAIN]http://img846.imageshack.us/img846/1269/img029z.jpg
2. The attempt at a solution
My attempt and relevant equation is only there in the picture. I know how to find the electric field of an infinite plane np, gaussian pillbox etc.
im not sure what role...
Hello everyone,
I'm a bit confused about electric dipole radiation. In my E&M book "Intro to Electrodynamics" by David Griffiths, it states that the electric field from an oscillating dipole is in theta hat direction. Mathematically I have the proof as to why in my book, but conceptually I'm...
Electric Dipole and Electric Potential.. and binomial approximation!
Homework Statement
An electric dipole at the origin consists of two charges +q and -q spaced distance s apart along the y-axis.
a.)Find an expression for the potential V(x,y) at an arbitrary point in the xy-plane...
This is part 2 of problem 4.8 from "Physics of Atoms and Molecules - Bransden, Joachain"
Homework Statement
Deduce [4.106] from [4.105]
Homework Equations
\tilde{M}_{ba} = - \frac{m\omega_{ba}}{\hbar c} \langle \psi _b \vert z \dot{x} \vert \psi _a \rangle [4.105]...
I am participating in a reading course on nonlinear optics, which is a little difficult since I haven't had any formal education in quantum mechanics other than the standard introductory solving of Schroedinger's eqn. in 1D. Happily this course takes the semiclassical approach, in which the...
Can someone help me with the derivation of the electric field at any point around a dipole. I DO NOT want the dipole moment to be resolved into components and then the field found out. I want it in terms of charge q (+q and -q constitute the dipole), a (2a being the charge separation), theta...
Homework Statement
find components of the electric field of a pure electric dipole (r>>a)Homework Equations
potential = \varphi(r)=2aqP1(cos\Theta)/4\pi\epsilonor2The Attempt at a Solution
do i just have to find the negative gradient of the potential here? i think that's the right thing to do...
Hi,
I had this question in my homework:
An electric dipole consists of two equal loads and signs opposite separated by one distance which equals 2a. Show how the module of the electric force resulting on a proton (load +e) placed directly on the Y=axis at a very long distance from the dipole...
Homework Statement
Charges + and -q are placed at -1cm and 1cm along the y axis. If their electric potential energy is -45microJ, what is q?
Homework Equations
U=qV
V=Es
The Attempt at a Solution
I got an equation for the electric potential between the two charges, but it was...
I have been wondering recently about the neutron dipole moment, after looking it up with the limited things available on the internet (to my knowledge anyway :) ) I have a few questions hopefully someone could answer for me. Firstly of the three symmetries, as I understand it, Parity, Charge...
Let's say I have a point dipole (as an approximation for an atom) at the origin and it oscillates in the z axis. The (theta component of the) electric field due to this dipole in the far field will be
E = \frac{d}{4\pi\epsilon_0}\frac{k^2\sin\theta}{r}\exp i\left(kr-\omega t\right)
where d is...
Homework Statement
Show that the field on the x-axis for the dipole (negative on the right, positive on the left separated by 2a) is given by the equation E = kq / x^3 for x >>a.
Homework Equations
Coulomb's Law F = kq1q2 / r^2
E = F/q = kQ / r^2
The Attempt at a Solution
Since...
Homework Statement
A 5mC charge is glued down at position ( 1m, 2m ). A -3mC charge is glued down at position ( -3m, -6m ). What are the components of the electric field at the point ( 7m, -6m )? If the component points in the negative direction, put in a negative number for your answer...
Homework Statement
Find rho(r,t) and j(r,t) for the following:
a) point charge q in uniform motion
b) electric dipole p in uniform motion
c) magnetic dipole m in uniform motion
Homework Equations
j(r,t) = v rho(r,t), so if we know rho, we know j
The Attempt at a Solution
a)...
Homework Statement
An infinite, vertical, nonconducting plane sheet is uniformly charged with electricity. Next to the sheet is a dipole that can freely oscillate about its midpoint O, which is at a distance Ж from the sheet. Each end of the dipole bears a charge q and a mass m. The length of...
Hi,
I have been wondering about a neutron dipole moment, though hypothetical what symmetries would it be violating, wouldn't it be Parity and Time reversal? If this were to be true, would it therefore make the statement below false and the word "inverted" would imply parity?
"T is the law of...
Homework Statement
Find the frequency of oscillation of an electric dipole, of dipole moment p and rotational inertia I, for small amplitudes of oscillation about its equilibrium position in a uniform electric field of magnitude E.
Answer: [(pE/I)^0.5]/(2*pi)
Homework Equations
I...
I'm reading in my organic chemistry text about the structure of alkyl halides, as a background to why certain reactions happen (specifically radical halogenation). In it there's a table of halomethanes, that tells the bond length, bond strength, and dipole moment. It pretty much looks like...