The Facts

• Ohm's law is a law of physics that states that the electrical current that flows through a conductor is directly proportional to the voltage applied to the conductor. The resistance of an electrical circuit is defined as the ratio of voltage to the electrical current. Therefore, Ohm's law is defined mathematically as I = V/R, where I is the electric current, V is the voltage and R is the resistance. The equation for conductivity comes from Ohm's law and is, typically, expressed as G = 1/R, where G is the conductivity and R is the resistance.
  
  

Features

• Conduction of an electrical current is facilitated by the charge of the ions found in the solution through which the current travels. Therefore, in general, the conductivity of a given solution is proportional to its ion concentration. While the measurement of conductivity depends on the given temperature of a solution, the degree to which temperature affects conductivity varies from solution to solution, according to "Conductivity Theory" at eidusa.com.
  
  

Measurement

• The basic unit of conductivity is the siemen, denoted by "S," and previously called the mho. Cell design and geometry are vital for accurate and precise conductivity measurements. As a result, standardized measurements are expressed in conductivity units, which are S/cm, to make up for variations in cell dimensions.
  
  

Considerations

• Furthermore, another measurement of conductivity is specific conductivity. Specific conductivity (C) is defined as the product of measured conductivity (G) and the cell constant (L/A), where L is the length of the column of solution between the cells and A is the area of the electrode cells. According to coleparmer.com, mathematically, this is written as C = G multiplied by L/A.
  
  

Types

• The surfaces of electrode conductivity cells are made from titanium, graphite, platinum or gold-plated nickel. While most conductivity meters only have two-electrode cells, some do come with four. Four-electrode cells are used as a reference voltage to make up for any polarization or fouling of the cells, according to coleparmer.com. The reference voltage ensures accuracy in conductivity measurements by indicating that the actual conductivity is independent of the condition of the electrode. Four cells are typically used for measuring conductivity over wide ranges.