Dipole

:This article is about the electromagnetic phenomenon. From the point of view of the mathematics of distributions, a dipole can be taken to be the directional derivative of a Dirac delta function. A dipole is also a type of radio antenna.

Related Topics:
Mathematics - Distribution - Dirac delta function - Dipole

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:For magnets in particle accelerators please see Dipole magnet.

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A dipole (Greek: dyo = two and polos = pivot) is a pair of electric charges or magnetic poles of equal magnitude but opposite polarity (opposite electronic charges), separated by some (usually small) distance. Dipoles can be characterized by their dipole moment, a vector quantity with a magnitude equal to the product of the charge or magnetic strength of one of the poles and the distance separating the two poles. The direction of the dipole moment corresponds to the direction from the negative to the positive charge or from the south to the north pole. (Because of the absence of magnetic monopoles, magnetic dipoles are actually created by current loops or by quantum-mechanical spin.)

Related Topics:
Greek - Electric charges - Moment - South - North pole - Magnetic monopoles - Spin

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Since the direction of an electric field is defined as the direction of the force on a positive charge, electric field lines point away from a positive charge and toward a negative charge. Since the direction of a magnetic field is defined as the direction of the force on a north magnetic pole, magnetic field lines point away from a north pole and towards a south pole.

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When placed in an electric (E) or magnetic (B) field, equal but opposite forces arise on each side of the dipole creating a torque τ:

Related Topics:
Electric - Magnetic - Force - Torque

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:τ = p × E (Electric dipole moment p)

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:τ = μ × B (Magnetic dipole moment μ)

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: (note: × corresponds to a vector cross product)

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which will tend to align the dipole with the field.

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