Chapter 7 Reference
7.1 Conductivity measurement
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73
Specific resistance (expressed in
Ω⋅
m) is an index that indicates the
difficulty with which current flows and is a constant determined
according to the solution. The inverse of r (expressed in
Ω⋅
m), which is L
(and is equal to 1/r), is called the “specific conductivity” and is widely
used as an index to express the ease with which current flows. Specific
conductivity L is generally referred to as simply “conductivity” and is
expressed in units of S/m.
Inserting conductivity L (expressed in S/m) into equation 1 results in
equation 2, below.
R = J/L (Equation 2)
As is clear from equation 2, when a conductivity cell having a cell
constant J of 1 m
-1
is used (in other words, when a conductivity cell
having two pole plates that each have an area a of 1 m
2
and are
positioned parallel to each other such that the distance l between the
two plates is 1 m is used) the inverse of the resistance R of the solution
(expressed in
Ω
) between both pole plates is the conductivity.
Conductivity is defined in this way, but it changes according to the
temperature of the solution.
The conductivity of a solution is generally expressed as the value when
the solution is 25ºC.
