Static Electricity 2000 Edition

D.1.15 Conductivity (
κκκκ) (l/resistivity).
(a) An intrinsic property of a solid or liquid that governs
the way electrical charges move across its surface or through
its bulk.
This property can be dramatically affected by the tempera-
ture and especially by the presence of moisture or antistats.
Conductors such as metals and aqueous solutions have a high
conductivity (low resistivity) and will lose charge quickly when
grounded. Insulators have a high resistivity and lose charge very
slowly, even when grounded. Conductors isolated from ground
can store charge and can rise to fairly high potentials in many
industrial situations, resulting in hazardous spark discharges.
The unit of conductivity is the ohm/m [note basis in recip-
rocal of resistivity with units of ohm-m; ohm/m is the same as
siemens per meter (S/m)]. Some authors express volume
resistivity data in terms of ohm-m (100 ohm-cm = 1 ohm-m).
Conductivity is not generally assigned to a gas. In gases,
free electrons or ions can be formed or injected by external
means. In the presence of an electric field, the ions migrate to
electrodes or charged surfaces and constitute a current. Con-
ductivity is rarely an intrinsic property of gas.
(b) Conductivity (electrical conductivity or specific con-
ductance) is the ratio of the electric current density to the
electric field in a material.
D.1.16 Cone Discharge.
See definition D.1.4, Bulking Brush
Discharge.
D.1.17 Corona Discharge.
An electrical discharge in the
microampere range that results from a localized electrical
breakdown of gases by charges on surfaces such as sharp
edges, needle points, and wires. The charges can arise on con-
ductors at high voltage or on grounded conductors that are
situated near a charged surface. Corona is accompanied by a
faint luminosity.
D.1.18 Coulomb.
A quantity of electrons equal to 6.24 
× 10
18
electrons; also, the quantity of electricity on the positive plate
of a capacitor of 1 farad capacitance when the potential differ-
ence across the plates is 1 volt.