General Formula for Apparent Resistivity If there are two current electrodes and two potential electrodes on the surface of a half-space, the configuration can be represented as follows:  It is not necessary that the four electrodes be in a straight line. If apparent resistivity is Ra and V is the difference in voltage between M and N then
 Most modern earth resistivity instruments report V/I as resistivity, R. Therefore  For a clear derivation of the above equation, see: Reynolds, J.M., 1997, An Introduction to Applied and Environmental Geophysics: New York, John Wiley & Sons, Inc. pp. 424-426 |
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