What is "dipole"

n. 1 (context physics English) any object (such as a magnet, polar molecule or antenna) that is oppositely charged at two points (or poles) 2 (context chemistry English) any molecule or radical that has delocalised positive and negative charges 3 (context radio English) a dipole antenna

1. n. a pair of equal and opposite electric charges or magnetic poles separated by a small distance

2. an aerial half a wavelength long consisting of two rods connected to a transmission line at the center [syn: dipole antenna]

In electromagnetism, there are two kinds of dipoles:

• An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some (usually small) distance. A permanent electric dipole is called an electret.
• A magnetic dipole is a closed circulation of electric current. A simple example of this is a single loop of wire with some constant current through it.

Dipoles can be characterized by their dipole moment, a vector quantity. For the simple electric dipole given above, 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 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.

In addition to current loops, the electron, among other fundamental particles, has a magnetic dipole moment. That is because it generates a magnetic field that is identical to that generated by a very small current loop. However, the electron's magnetic moment is not due to a current loop, but is instead an intrinsic property of the electron. It is also possible that the electron has an electric dipole moment although it has not yet been observed (see electron electric dipole moment for more information).

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), 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. The north pole of a bar magnet in a compass 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 (dis), "twice" and (polos), "axis".

In physics, a dipole is a quantity involved some form of polarity

• Electric dipole
• Magnetic dipole
• Dipole moment (disambiguation)
• A flow dipole, a separation of a sink and a source in potential flow.

In meteorology:

• Arctic dipole anomaly
• Indian Ocean Dipole

It may also refer to:

• Dipole antenna, a type of radio antenna
• Dipole magnet, a permanent magnet
• Dipole graph, a graph with two poles
• Dipole speaker, a loudspeaker enclosure
• Dipole model of the Earth's magnetic field - the Earth's magnetic field can be viewed as dipolar (first order approximation).
• Dipole anisotropy in Cosmology it has the property of being directionally dependent and is relative to the observer because one end of the 360-degree spectrum is redshifted, whereas the other end is blueshifted.
• Dipole–dipole attraction is one of several intermolecular forces.