Question

What is Cell Constant?

Answer 1

1. The resistance of a conductor ($R$) is directly proportional to its length ($l$) and cross-sectional area ($A$) as given by the equation $R=\rho \frac{l}{A}$ where $\rho$ is called the Specific Resistance of the conductor. It is the resistance of a conductor having a length $l=1m$ and cross-sectional area $A=1m^2$.
2. For electrolytes, the specific resistance is measured using an apparatus called a conductivity cell. The specific resistance is the resistance of that volume of electrolyte enclosed between the electrodes of a conductivity cell having a surface area of $1m^2$ and placed $1m$apart. The volume of the electrolyte enclosed by such electrodes is $1m^3$. Thus, the specific resistance of an electrolyte is the resistance of $1m^3$ of the electrolyte. Its SI unit is ohm metre ($\Omega m$).
3. The reciprocal of specific resistance ($\rho$) is called specific conductance, denoted by $\kappa$ (kappa). The specific conductance of an electrolyte is the conductance (reciprocal of resistance) of that volume of electrolyte which is enclosed between the electrodes of a conductivity cell having a surface area of $1m^2$ when placed $1m$ apart as given by the equation $\kappa =\left(\frac{1}{R}\right)\left(\frac{l}{A}\right)$ where $\frac{1}{R}$is the conductance denoted by $G$. SI unit of specific conductance is siemens per meter ($S{m}^{-1}$) where siemens ($S$) is the SI unit of conductance.
4. In the equation of specific conductance, the quantity $\frac{l}{A}$is called the Cell Constant and it is denoted as $G*$. Cell constant has the dimension $lengt{h}^{-1}$. Its SI unit is $m^{-1}$.
5. Thus, the cell constant of a conductivity cell is the ratio of the distance between the electrodes of the cell to their surface area.