A nonconductor of electric charge in which an applied electric field causes a displacement of charge but not a flow of charge. Electrons within the atoms of a dielectric are, on average, displaced by an applied field with respect to the nucleus, giving rise to a dipole (a pair of separated electric charges) that has an electric moment in the direction of the field. The resulting stress within the dielectric is known as electric polarization (P). The dielectric strength is the maximum potential gradient that can be applied to a material without causing it to break down. It is usually expressed in volts per millimetre.