1. A charge distribution that generates an electric field equal to that produced by two electric dipoles whose moments have the same magnitude, but extend in opposite directions a small distance apart.
2. A charge distribution that produces an electric field equivalent to what is produced by two electric dipoles whose dipole moments have the same magnitude, but point in opposite directions and which are separate from each other by a small distance.

1. A device, consisting of four electrodes arranged in alternating polarity, which focuses a beam of charged particles.
2. An instrument for focusing beams of charged particles which has four electrodes with alternately positive and negative polarity; used in electron microscopes and particle accelerators.
3. An apparatus that uses four electrodes set in an alternating positive-negative polarity series to focus the beams of charged particles employed in electron microscopes and particle accelerators.

A quantity characterizing an electric charge distribution, obtained by integrating the product of the charge density, the second power of the distance from the origin, and a spherical harmonic over the charge distribution.

1. A transition of an atom or molecule from one energy state to another, in which electric quadrupole radiation is emitted or absorbed.
2. A process in which an atom produces or absorbs quadrupole radiation when it changes from one energy level to another.