What Are the Units of Conductivity?

Units

• Formerly, the International System of Units used MHO, a backward spelling of Ohm, as an informal unit of conductivity. However, although MHO may still be used by some practitioners today, the Siemens (S) is now known as the basic unit of conductivity. If an electrode has varying dimensions, you may also see a unit such as S/cm, where Siemens is measured with respect to a specific dimension or distance. Specific conductivity, symbolized by C, is the product of measured conductivity (G) and a given electrode cell constant (L/A). The electrode cell constant is the length of an electrode's column divided by the area of the electrode.

How Conductivity Is Determined

• Two conductive plates are placed in a sample of the material being tested for conductivity. An electric potential, usually in the form of a sine wave voltage, is placed across the plates. Once the plates are charged, current either passes across the sample to the second plate or the material is resistant enough to prevent a portion or all of the current from passing. Any current that does pass through the sample material to reach the second plate is measured by a multimeter or an amp meter.

Ohm's Law

• Ohm's law is a well-known formula for dealing with basic electronics and electrical circuits. The Ohm, symbolized by a capital Greek omega, is known as the inverse of conductivity. An Ohm is also referred to as the resistance capacity of an object. There are several versions of Ohm's law. This is its most basic form: voltage = current x resistance. Ohm's law allows the derivation of 12 different formulas for use with any given electrical problem.

Other Electrical Units

• Current is measured in amps or amperes (A). You might compare the flow of current through a wire or conductor to water flowing in a river. Voltage (E in a formula and V as a unit) is the difference between the electrical potential of two different points in a given circuit. Voltage may be thought of as the gravity or change in elevation that causes the water to flow at a certain rate. Resistance (R) measures the amount of current that is allowed to flow through a medium. The more resistance a medium has, the less current and voltage the medium will carry. Power, measured in watts, is the product of the current and the voltage.