Archive for the ‘Electrical Conductivity’ category

Electrical Conductivity-Principle of its Measurement

April 28th, 2014

Electrical Conductivity is a measure of the ability of a substance/solution to conduct an Electric Current (this electric current is carried by ions and the chemical changes that occur in the solution).

Electric Conductivity depends on:

  • Concentration of ions (higher concentration, higher Electrical Conductivity); the determination of the Electrical Conductivity is a rapid and convenient means of estimating the concentration of ions in solution. Since each ion has its own specific ability to conduct current, Electrical Conductivity is only an estimate of the total ion concentration.
  • Temperature of the solution (higher temperature, higher Electrical Conductivity); The Conductivity of a solution is highly temperature dependent, therefore it is important to either use a temperature compensated instrument, or calibrate the instrument at the same temperature as the solution being measured.
  • Specific nature of the ions (higher specific ability and higher valence, higher electric conductivity)

An Electrical Conductivity meter (EC meter) measures the Electrical Conductivity in a solution. Conductivity changes with storage time and temperature.

Principle by which this instrument measures the Electrical Conductivity is very simple; two plates are placed in a sample, a potential is applied across the plates (normally a sine wave voltage), and the current is measured.

Electrical Conductivity is denoted by symbol sigma (σ) and its SI unit is Siemens per metre (S·m−1). Reverse of Electrical Conductivity is known as Electrical Resistivity, which is denoted by symbol rho (ρ).

Electrical conductivity (σ) =             1

Electrical resistivity (ρ)

Relation between potential (V) and current (I) is given by Ohm’s law. According to Ohm’s law current increases with the increase in potential.

i.e.                                V α I

V = RI    (Proportionality constant called Resistance)

R = V/I                                                                                                                                     

Resistance also depends on the temperature; increase in temperature decreases the Resistance.