Pair of equal and opposite
An {{link=atom">atom in which the centre of the negative cloud of electron s has been shifted slightly away from the nucleus by an external electric field is an induced electric dipole. When the external field is removed, the atom loses its dipolarity. A water molecule, in which two hydrogen atoms are situated to one side of an oxygen atom, is a permanent electric dipole. The oxygen side is always slightly negative, the hydrogen side slightly positive.